Nonsurgical Treatment of Acetabular Labral Tears.

PubMed

Theige, Melissa; David, Shannon

2018-05-04

Clinical Scenario: Surgical treatment of acetabular labral tears has been explored in multiple studies, while there is a lack of research on the effectiveness of conservative methods. Focused Clinical Question: To what extent can nonsurgical treatment produce symptomatic or functional improvements in athletes with an acetabular labral tear? Summary of Search, Best Evidence Appraised, and Key Findings: The literature was searched for studies of patients with confirmed acetabular labral tears who participated in any level of sport. Four studies were located, all of which were included. Clinical Bottom Line: The research discussed in this review agreed that conservative management of acetabular labral tears produced measurable improvements in pain and function among the athletes studied, including their ability to participate in sport activities. Based on these findings, it appears that conservative management is effective at rehabilitating athletes with acetabular labral tears. However, this method should not be applied to every athlete based on the low strength of current research. Treatment plans should be decided upon on a case-by-case basis. Strength of Recommendation: The studies located were of low quality. The highest Oxford Center for Evidence-Based Medicine Level of Evidence achieved was 4. Higher level studies must be conducted before the conclusions of this research can be applied clinically with assertion. Strength of recommendation is level 3.

A novel electromagnetic navigation tool for acetabular surgery.

PubMed

Lehmann, Wolfgang; Rueger, Johannes M; Nuechtern, Jakob; Grossterlinden, Lars; Kammal, Michael; Hoffmann, Michael

2015-10-01

Acetabular fracture surgery is demanding and screw placement along narrow bony corridors remains challenging. It necessitates x-ray radiation for fluoroscopically assisted screw insertion. The purpose of this cadaver study was to evaluate the feasibility, accuracy and operation time of a novel electromagnetic navigation system for screw insertion along predefined acetabular corridors. A controlled laboratory study with a total of 24 electromagnetically navigated screw insertions was performed on 8 cadaveric acetabula. 3 peri-acetabular bony corridors (QSS, Quadrilateral Surface Screw; IAS, Infra-Acetabular Screw; PCS, Posterior Column Screw) were defined and screws were placed in a defined order without fluoroscopy. Operation time was documented. Postoperative CT scans were performed to analyse accuracy of screw placement. Mean cadaver age was 70.4 ± 11.7. Successful screw placement was accomplished in 22 out of 24 (91.7%) cases. The overall mean time for all 3 acetabular screws was 576.6 ± 75.9s. All 3 complications occurred during the placement of the IAS due to an impassable narrow bony corridor. QSS mean length was 50 ± 5mm, IAS mean length was 85 ± 10mm and PCS mean length was 120 ± 5mm. In this cadaver study the novel electromagnetic navigation system was feasible to allow accurate screw placement without fluoroscopy in defined narrow peri-acetabular bony corridors. Copyright © 2015 Elsevier Ltd. All rights reserved.

[Contact characteristics research of acetabular weight-bearing area with different internal fixation methods after compression fracture of acetabular dome].

PubMed

Xu, Bowen; Zhang, Qingsong; An, Siqi; Pei, Baorui; Wu, Xiaobo

2017-08-01

To establish the model of compression fracture of acetabular dome, and to measure the contact characteristics of acetabular weight-bearing area of acetabulum after 3 kinds of internal fixation. Sixteen fresh adult half pelvis specimens were randomly divided into 4 groups, 4 specimens each group. Group D was the complete acetabulum (control group), and the remaining 3 groups were prepared acetabular dome compression fracture model. The fractures were fixed with reconstruction plate in group A, antegrade raft screws in group B, and retrograde raft screws in group C. The pressure sensitive films were attached to the femoral head, and the axial compression test was carried out on the inverted single leg standing position. The weight-bearing area, average stress, and peak stress were measured in each group. Under the loading of 500 N, the acetabular weight-bearing area was significantly higher in group D than in other 3 groups ( P <0.05), and the average stress and peak stress were significantly lower than in other 3 groups ( P <0.05). The acetabular weight-bearing area were significantly higher in group B and group C than in group A, and the average stress and peak stress were significantly lower than in group A ( P <0.05). There was no significant difference in the above indexes between group B and group C ( P >0.05). For the compression fracture of the acetabular dome, the contact characteristics of the weight-bearing area can not restore to the normal level, even if the anatomical reduction and rigid internal fixation were performed; compared with the reconstruction plate fixation, antegrade and retrograde raft screws fixations can increase the weight-bearing area, reduce the average stress and peak stress, and reduce the incidence of traumatic arthritis.

Acetabular-epiphyseal angle and hip dislocation in cerebral palsy: a preliminary study.

PubMed

Alí-Morell, O J; Zurita-Ortega, F; Davó-Jiménez, I; Segura-Biedma, S

To relate, in non-ambulatory subjects with palsy, Reimers' migration percentage with standardized radiological measurements, including the acetabular-epiphyseal angle. Descriptive, observational and transversal study of 15 individuals with cerebral palsy at levels IV and V of the Gross Motor Function Classification System, aged between 3 and 9 years. Radiological measurements of the acetabular index, Hilgenreiner's epiphyseal angle, acetabular-epiphyseal angle, neck-shaft angle and Reimers' migration percentage of each of the hips were performed. Correlations between acetabular index, epiphyseal angle and acetabular-epiphyseal angle were obtained with respect to the Reimers migration percentage. For hips with a migration rate of 15% or less, a positive correlation was observed between acetabular and epiphyseal angles. In our population, the measurement between acetabular and epiphyseal inclination represents the highest association with the hip migration percentage. Copyright © 2018 SERAM. Publicado por Elsevier España, S.L.U. All rights reserved.

Polyethylene wear debris in modular acetabular prostheses.

PubMed

Chen, P C; Mead, E H; Pinto, J G; Colwell, C W

1995-08-01

The longevity of total hip arthroplasty has brought forth the recognition of aseptic loosening of prosthetic components as the leading cause of implant failure. Modularity of implants, although a significant improvement in versatility, may increase debris formation, a recognized cause of implant failure. This study was designed to measure the relative motion, and to assess the polyethylene wear debris production at the interface between the metal acetabular shell and the back side of the polyethylene liner, in modular hip prostheses. Five models from 4 manufacturers with different locking mechanisms and acetabular shell surface treatments were tested under long-term simultaneous sinusoidal and static loading (10(7) cycles at 3 Hz with +/- 2.5 Nmeter and 220 N static load). Results showed that there were marked differences in the security of the acetabular shell and polyethylene liner locking mechanism, wear pattern, damage sites, and amount of polyethylene debris on the acetabular shell and polyethylene liner surfaces. The range of polyethylene liner motion observed among the 5 models during 1 cycle of testing varied from an average of 0.96 degrees to movement too small to be detected by the test machines. Image and scanning electron microscopy analysis showed different wear patterns and a wide range in the average polyethylene liner surface wear area (0.26 cm2-4.61 cm2). In general, a stable locking mechanism and a smooth acetabular shell surface are essential in minimizing polyethylene liner wear and polyethylene debris production.

[Quantification of acetabular coverage in normal adult].

PubMed

Lin, R M; Yang, C Y; Yu, C Y; Yang, C R; Chang, G L; Chou, Y L

1991-03-01

Quantification of acetabular coverage is important and can be expressed by superimposition of cartilage tracings on the maximum cross-sectional area of the femoral head. A practical Autolisp program on PC AutoCAD has been developed by us to quantify the acetabular coverage through numerical expression of the images of computed tomography. Thirty adults (60 hips) with normal center-edge angle and acetabular index in plain X ray were randomly selected for serial drops. These slices were prepared with a fixed coordination and in continuous sections of 5 mm in thickness. The contours of the cartilage of each section were digitized into a PC computer and processed by AutoCAD programs to quantify and characterize the acetabular coverage of normal and dysplastic adult hips. We found that a total coverage ratio of greater than 80%, an anterior coverage ratio of greater than 75% and a posterior coverage ratio of greater than 80% can be categorized in a normal group. Polar edge distance is a good indicator for the evaluation of preoperative and postoperative coverage conditions. For standardization and evaluation of acetabular coverage, the most suitable parameters are the total coverage ratio, anterior coverage ratio, posterior coverage ratio and polar edge distance. However, medial coverage and lateral coverage ratios are indispensable in cases of dysplastic hip because variations between them are so great that acetabuloplasty may be impossible. This program can also be used to classify precisely the type of dysplastic hip.

Periacetabular Osteotomy Provides Higher Survivorship Than Rim Trimming for Acetabular Retroversion.

PubMed

Zurmühle, Corinne A; Anwander, Helen; Albers, Christoph E; Hanke, Markus S; Steppacher, Simon D; Siebenrock, Klaus A; Tannast, Moritz

2017-04-01

Acetabular retroversion can cause impaction-type femoroacetabular impingement leading to hip pain and osteoarthritis. It can be treated by anteverting periacetabular osteotomy (PAO) or acetabular rim trimming with refixation of the labrum. There is increasing evidence that acetabular retroversion is a rotational abnormality of the entire hemipelvis and not a focal overgrowth of the anterior acetabular wall, which favors an anteverting PAO. However, it is unknown if this larger procedure would be beneficial in terms of survivorship and Merle d'Aubigné scores in a midterm followup compared with rim trimming. We asked if anteverting PAO results in increased survivorship of the hip compared with rim trimming through a surgical hip dislocation in patients with symptomatic acetabular retroversion. We performed a retrospective, comparative study evaluating the midterm survivorship of two matched patient groups with symptomatic acetabular retroversion undergoing either anteverting PAO or acetabular rim trimming through a surgical hip dislocation. Acetabular retroversion was defined by a concomitantly present positive crossover, posterior wall, and ischial spine sign. A total of 279 hips underwent a surgical intervention for acetabular retroversion at our center between 1997 and 2012 (166 periacetabular osteotomies, 113 rim trimmings through surgical hip dislocation). A total of 99 patients (60%) were excluded from the PAO group and 56 patients (50%) from the rim trimming group because they had any of several prespecified conditions (eg, dysplasia or pediatric conditions 61 [37%] for the PAO group and two [2%] for the rim trimming group), matching (10 [6%]/10 [9%] hips), deficient records (10 [6%]/13 [12%] hips), or the patient declined or was lost to followup (18 [11%]/31 [27%] hips). This left 67 hips (57 patients) that underwent anteverting PAO and 57 hips (52 patients) that had acetabular rim trimming. The two groups did not differ in terms of age, sex, body mass

Evaluation of the three-dimensional bony coverage before and after rotational acetabular osteotomy.

PubMed

Tanaka, Takeyuki; Moro, Toru; Takatori, Yoshio; Oshima, Hirofumi; Ito, Hideya; Sugita, Naohiko; Mitsuishi, Mamoru; Tanaka, Sakae

2018-02-26

Rotational acetabular osteotomy is a type of pelvic osteotomy that involves rotation of the acetabular bone to improve the bony coverage of the femoral head for patients with acetabular dysplasia. Favourable post-operative long-term outcomes have been reported in previous studies. However, there is a paucity of published data regarding three-dimensional bony coverage. The present study investigated the three-dimensional bony coverage of the acetabulum covering the femoral head in hips before and after rotational acetabular osteotomy and in normal hips. The computed tomography data of 40 hip joints (12 joints before and after rotational acetabular osteotomy; 16 normal joints) were analyzed. The three-dimensional bony coverage of each joint was evaluated using original software. The post-operative bony coverage improved significantly compared with pre-operative values. In particular, the anterolateral aspect of the acetabulum tended to be dysplastic in patients with acetabular dysplasia compared to those with normal hip joints. However, greater bony coverage at the anterolateral aspect was obtained after rotational acetabular osteotomy. Meanwhile, the results of the present study may indicate that the bony coverage in the anterior aspect may be excessive. Three-dimensional analysis indicated that rotational acetabular osteotomy achieved favorable bony coverage. Further investigations are necessary to determine the ideal bony coverage after rotational acetabular osteotomy.

Combat-related acetabular fractures: Outcomes of open versus closed injuries.

PubMed

Purcell, Richard L; Donohue, Michael A; Saxena, Sameer K; Gordon, Wade T; Lewandowski, Louis L

2018-02-01

Since the onset of the Global War on Terror close to 50,000 United States service members have been injured in combat, many of these injuries would have previously been fatal. Among these injuries, open acetabular fractures are at an increased number due to the high percentage of penetrating injuries such as high velocity gunshot wounds and blast injuries. These injuries lead to a greater degree of contamination, and more severe associated injuries. There is a significantly smaller proportion of the classic blunt trauma mechanism typically seen in civilian trauma. We performed a retrospective review of the Department of Defense Trauma Registry into which all US combat-injured patients are enrolled, as well as reviewed local patient medical records, and radiologic studies from March 2003 to April 2012. Eighty seven (87) acetabular fractures were identified with 32 classified as open fractures. Information regarding mechanism of injury, fracture pattern, transfusion requirements, Injury Severity Score (ISS), and presence of lower extremity amputations was analyzed. The mechanism of injury was an explosive device in 59% (n=19) of patients with an open acetabular fracture; the remaining 40% (n=13) were secondary to ballistic injury. In contrast, in the closed acetabular fracture cohort 38% (21/55) of fractures were due to explosive devices, and all remaining (n=34) were secondary to blunt trauma such as falls, motor vehicle collisions, or aircraft crashes. Patients with open acetabular fractures required a median of 17units of PRBC within the first 24h after injury. The mean ISS was 32 in the open group compared with 22 in the closed group (p=0.003). In the open fracture group nine patients (28%) sustained bilateral lower extremity amputations, and 10 patients (31%) ultimately underwent a hip disarticulation or hemi-pelvectomy as their final amputation level. Open acetabular fractures represent a significant challenge in the management of combat-related injuries. High

Acetabular inclination and anteversion in infants using 3D MR imaging.

PubMed

Falliner, A; Muhle, C; Brossmann, J

2002-03-01

To establish if 3D MR imaging could be used for measurements of acetabular inclination and anteversion in infants specimens. 3D MR data of 3 pelvic preparations of 6-week- to 10-month-old infant specimens was gathered. MR imaging in transaxial and frontal planes was carried out to measure the acetabular inclination and anteversion: a method to determine the MR planes for measurements is described. It was oriented on anatomical landmarks of the pelvis and therefore allowed adjustment of the frontal and transaxial planes, independent of the pelvis position. The mean acetabular inclination angle was 48 degrees, and the mean acetabular anteversion was 23 degrees. Because of the low number of cases the results can only be assessed as a tendency, but MR imaging seems to be suitable for measurements of acetabular inclination and anteversion.

A novel method to assess primary stability of press-fit acetabular cups.

PubMed

Crosnier, Emilie A; Keogh, Patrick S; Miles, Anthony W

2014-11-01

Initial stability is an essential prerequisite to achieve osseointegration of press-fit acetabular cups in total hip replacements. Most in vitro methods that assess cup stability do not reproduce physiological loading conditions and use simplified acetabular models with a spherical cavity. The aim of this study was to investigate the effect of bone density and acetabular geometry on cup stability using a novel method for measuring acetabular cup micromotion. A press-fit cup was inserted into Sawbones(®) foam blocks having different densities to simulate normal and osteoporotic bone variations and different acetabular geometries. The stability of the cup was assessed in two ways: (a) measurement of micromotion of the cup in 6 degrees of freedom under physiological loading and (b) uniaxial push-out tests. The results indicate that changes in bone substrate density and acetabular geometry affect the stability of press-fit acetabular cups. They also suggest that cups implanted into weaker, for example, osteoporotic, bone are subjected to higher levels of micromotion and are therefore more prone to loosening. The decrease in stability of the cup in the physiological model suggests that using simplified spherical cavities to model the acetabulum over-estimates the initial stability of press-fit cups. This novel testing method should provide the basis for a more representative protocol for future pre-clinical evaluation of new acetabular cup designs. © IMechE 2014.

21 CFR 888.3370 - Hip joint (hemi-hip) acetabular metal cemented prosthesis.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Hip joint (hemi-hip) acetabular metal cemented... HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3370 Hip joint (hemi-hip) acetabular metal cemented prosthesis. (a) Identification. A hip joint (hemi-hip) acetabular...

A Novel Approach for Treatment of Acetabular Fractures

PubMed Central

Xue, Zichao; Qin, Hui; Ding, Haoliang; An, Zhiquan

2016-01-01

Background There is no single approach that provides adequate exposure for treatment of all types of acetabular fractures. We describe our experience with an easier, relatively less invasive pubic symphysis approach (PSA) for the treatment of acetabular fractures. Material/Methods Between March 2011 and March 2012, fifteen patients with acetabular fracture underwent surgery using the PSA technique. Fracture reduction and treatment outcomes were assessed by clinical and radiological examination. Operation time, intraoperative blood loss and postoperative complications were documented. Results Mean operative time was 222±78 minutes. Average blood loss was 993±361 mL. Anatomical reduction was achieved in all patients. Minimum follow-up period was 31 months. Postoperative hypoesthesia in the area of innervation of the lateral femoral cutaneous nerve was reported in one patient, with spontaneous recovery at one month after surgery. No complications were reported during the follow-up period. At the most recent follow up, clinical outcomes were graded as “excellent” in six patients, “good” in eight patients and “fair” in one patient based on the modified Merle d’Aubigné-Postel score. Conclusions PSA appears to be a timesaving and safe approach for treatment of acetabular fractures that affords good visual access and allows for excellent fracture reduction. Our preliminary results revealed a much lower incidence of complications than traditional approaches, suggesting PSA is an alternative for treatment of acetabular fractures. PMID:27734825

Acetabular labral tears in patients with sports injury.

PubMed

Kang, Chan; Hwang, Deuk-Soo; Cha, Soo-Min

2009-12-01

We wanted to investigate acetabular labral tears and their correlation with femoroacetabular impingement in patients with sports injury. Among 111 patients who were diagnosed with the acetabular labral tears after arthroscopic treatment from January 2004 to December 2007, we selected 41 patients with sports injury. There were 12 cases of Taekwondo injury, 5 of golf injury, 4 of soccer injury, 3 of gymnastics injury, 2 of Hapkido injury, 2 of aerobics injury, 2 of rock-climbing injury, 2 of fitness training injury and 9 of other sports injuries. We checked the subtypes of acetabular labral tears and the accompanying femoroacetabular impingement. For the cases with accompanying femoroacetabular impingement, we investigated the subtypes according to the types of sports, gender and age. At last follow-up, we checked the Harris Hip Score (HHS), the Hip Outcome Score (HOS) sports scale and the percentage of patients who returned to their sports activity. The average age of symptomatic onset was 26 years (range, 12 to 65 years). The ratio of males to females was 29 : 12. An average duration of the hip pain was 17 months (range, 1 to 60 months). The degenerative type of acetabular labral tears was the most prevalent with 32 cases (78%), and there were 9 cases (22%) of the partial tear type. Thirty cases (73%) were accompanied by femoroacetabular impingement. The average age of the 23 cases (56%) of the cam-type was 23 years (range, 12 to 48 years), and it was more likely to occur in men (87%) and for people practicing martial arts such as Taekwondo or Hapkido. An average age of the 5 cases (12%) of the pincer-type was 26 (range, 16 to 43 years), it usually occurred in women (60%) and for non-martial arts such as golf and gymnastics. There were 2 cases of the mixed type (cam + pincer-type). At 27 months follow-up, the HHS was 61 to 92 points, the HOS sports scale increased 43 to 75%, and the rate of returning to sports was 71%. In spite of the early expression of symptoms

Sarcopenia Is Predictive of 1-Year Mortality After Acetabular Fractures in Elderly Patients.

PubMed

Mitchell, Phillip M; Collinge, Cory A; OʼNeill, David E; Bible, Jesse E; Mir, Hassan R

2018-06-01

To determine whether sarcopenia is an independent predictor of mortality in geriatric acetabular fractures. Retrospective cohort. American College of Surgeons Level I trauma center. One hundred and forty-six patients over the age 60 with acetabular fractures treated at our institution over a 12-year period. The primary outcome was 1-year mortality, collected using the Social Security Death Index. We used the psoas:lumbar vertebral index (PLVI), calculated using the cross-sectional area of the L4 vertebral body and the left and right psoas muscles, to assess for sarcopenia. Using a multivariate logistic regression model, we found that low PLVI was associated with increased 1-year mortality (P = 0.046) when controlling for age, gender, Charlson Comorbidity Index, Injury Severity Score (ISS), smoking status, and associated pelvic ring injury. Increasing age and ISS also showed a relationship with 1-year mortality in this cohort (P < 0.001, P < 0.001, respectively). We defined sarcopenia as those patients in the lowest quartile of PLVI. The mortality rate of this cohort was 32.4%, compared with 11.0% in patients without sarcopenia (odds ratio 4.04; 95% confidence interval 1.62-10.1). Age >75 years, ISS >14, and sarcopenia had 1-year mortality rates of 37.1%, 30.9%, and 32.4%, respectively. In patients with all 3 factors, the mortality rate was 90%. Sarcopenia is an independent risk factor for 1-year mortality in elderly patients with acetabular fractures. This study highlights the importance of objective measures to assess frailty in elderly patients who have sustained fractures about the hip and pelvis. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

21 CFR 888.3370 - Hip joint (hemi-hip) acetabular metal cemented prosthesis.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Hip joint (hemi-hip) acetabular metal cemented... (hemi-hip) acetabular metal cemented prosthesis. (a) Identification. A hip joint (hemi-hip) acetabular metal cemented prosthesis is a device intended to be implanted to replace a portion of the hip joint...

Safe surgical technique for associated acetabular fractures

PubMed Central

2013-01-01

Associated acetabular fractures are challenging injuries to manage. The complex surgical approaches and the technical difficulty in achieving anatomical reduction imply that the learning curve to achieve high-quality care of patients with such challenging injuries is extremely steep. This first article in the Journal’s “Safe Surgical Technique” section presents the standard surgical care, in conjunction with intraoperative tips and tricks, for the safe management of all subgroups of associated acetabular fractures. PMID:23414782

Intraoperative fluoroscopic evaluation of screw placement during pelvic and acetabular surgery.

PubMed

Yi, Chengla; Burns, Sean; Hak, David J

2014-01-01

The surgical treatment of pelvic and acetabular fractures can be technically challenging. Various techniques are available for the reconstruction of pelvic and acetabular fractures. Less invasive percutaneous fracture stabilization techniques, with closed reduction or limited open reduction, have been developed and are gaining popularity in the management of pelvic and acetabular fractures. These techniques require knowledge and interpretation of various fluoroscopic images to ensure appropriate and safe screw placement. Given the anatomic complexity of the intrapelvic structures and the 2-dimensional nature of standard fluoroscopy, multiple images oriented in different planes are needed to assess the accuracy of guide wire and screw placement. This article reviews the fluoroscopic imaging of common screw orientations during pelvic and acetabular surgery.

Validation of a new radiographic measurement of acetabular version: the transverse axis distance (TAD).

PubMed

Nitschke, Ashley; Lambert, Jeffery R; Glueck, Deborah H; Jesse, Mary Kristen; Mei-Dan, Omer; Strickland, Colin; Petersen, Brian

2015-11-01

This study has three aims: (1) validate a new radiographic measure of acetabular version, the transverse axis distance (TAD) by showing equivalent TAD accuracy in predicting CT equatorial acetabular version when compared to a previously validated, but more cumbersome, radiographic measure, the p/a ratio; (2) establish predictive equations of CT acetabular version from TAD; (3) calculate a sensitive and specific cut point for predicting excessive CT acetabular anteversion using TAD. A 14-month retrospective review was performed of patients who had undergone a dedicated MSK CT pelvis study and who also had a technically adequate AP pelvis radiograph. Two trained observers measured the radiographic p/a ratio, TAD, and CT acetabular equatorial version for 110 hips on a PACS workstation. Mixed model analysis was used to find prediction equations, and ROC analysis was used to evaluate the diagnostic accuracy of p/a ratio and TAD. CT equatorial acetabular version can accurately be predicted from either p/a ratio (p < 0.001) or TAD (p < 0.001). The diagnostic accuracies of p/a ratio and TAD are comparable (p =0.46). Patients whose TAD is higher than 17 mm may have excessive acetabular anteversion. For that cutpoint, the sensitivity of TAD is 0.73, with specificity of 0.82. TAD is an accurate radiographic predictor of CT acetabular anteversion and provides an easy-to-use and intuitive point-of-care assessment of acetabular version in patients with hip pain.

Three-dimensional finite analysis of acetabular contact pressure and contact area during normal walking.

PubMed

Wang, Guangye; Huang, Wenjun; Song, Qi; Liang, Jinfeng

2017-11-01

This study aims to analyze the contact areas and pressure distributions between the femoral head and mortar during normal walking using a three-dimensional finite element model (3D-FEM). Computed tomography (CT) scanning technology and a computer image processing system were used to establish the 3D-FEM. The acetabular mortar model was used to simulate the pressures during 32 consecutive normal walking phases and the contact areas at different phases were calculated. The distribution of the pressure peak values during the 32 consecutive normal walking phases was bimodal, which reached the peak (4.2 Mpa) at the initial phase where the contact area was significantly higher than that at the stepping phase. The sites that always kept contact were concentrated on the acetabular top and leaned inwards, while the anterior and posterior acetabular horns had no pressure concentration. The pressure distributions of acetabular cartilage at different phases were significantly different, the zone of increased pressure at the support phase distributed at the acetabular top area, while that at the stepping phase distributed in the inside of acetabular cartilage. The zones of increased contact pressure and the distributions of acetabular contact areas had important significance towards clinical researches, and could indicate the inductive factors of acetabular osteoarthritis. Copyright © 2016. Published by Elsevier Taiwan.

Debonding of porous coating of a threaded acetabular component: retrieval analysis.

PubMed

Łapaj, Łukasz; Markuszewski, Jacek; Rybak, Tomasz; Wierusz-Kozłowska, Małgorzata

2013-01-01

This report presents a case of debonding of plasma sprayed porous titanium coating from a threaded acetabular component which caused aseptic loosening of the implant. Weight bearing after delamination caused abrasive damage of the acetabular shell, and particles of the coating embedded in the acetabular liner. Microscopic examination of periprosthetic tissues showed presence of metal particles and macrophage infiltration. Despite microscopic examination of the retrieved component the cause of debonding remains unclear. Copyright © 2012 Elsevier Ltd. All rights reserved.

Bone preserving techniques for explanting the well-fixed cemented acetabular component.

PubMed

Stevens, Jarrad; Macpherson, Gavin; Howie, Colin

2018-06-01

Removal of a well-fixed, cemented acetabular component at the time of revision hip surgery can be complex. It is essential to remove the implant and cement mantle in a timely fashion while preserving bone stock and osseous integrity. The biomechanical properties of polymethylmethacrylate cement and polyethylene can be utilised to aid with the removal of well cemented implants which are often harder than the surrounding bone. While removal of loose components may be relatively straightforward, the challenge for the revision arthroplasty surgeon often involves the removal of well-fixed implants. Here, we present three established techniques for the removal of a well-fixed cemented acetabular component and one novel modification we have described before. We collate and review four techniques for removing well-fixed cemented acetabular implants that utilise the different biomechanical properties of bone cement and polyethylene. These techniques are illustrated with a photographic series utilising saw bones. A step-by-step approach to our new technique is shown in photographs, both in the clinical setting and with a "Sawbone". This is accompanied by a clinical video that details the surgical technique in its entirety. These techniques utilise different biomechanical principles to extract the acetabular component. Each technique has advantages and disadvantages. Our new technique is a simplification of a previously published extraction manoeuvre that utilises tensile force between cement and the implant to remove the polyethylene cup. This is a safe and reproducible technique in patients with a well-fixed cemented acetabular implant. Understanding the biomechanical properties of polymethylmethacrylate bone cement and polyethylene can aid in the safe removal of a well-fixed cemented acetabular component in revision hip surgery. The optimal technique for removal of a cemented acetabular component varies depending on a number of patient and implant factors. This summary of

Controversies in Treatment of Acetabular Fracture

PubMed Central

Grubor, Predrag; Krupic, Ferid; Biscevic, Mirza; Grubor, Milan

2015-01-01

Introduction: Acetabular fractures treatment represents a great controversy, challenge and dilemma for an orthopedic surgeon. Aim: The aim of the paper was to present the results of treatment of 96 acetabular fractures in the Clinic of Traumatology Banja Luka, in the period from 2003 to 2013, as well as to raise awareness regarding the controversy in the methods of choice in treating acetabulum fractures. Material and methods: The series consists of 96 patients, 82 males and 14 females, average age 40.5 years. Traffic trauma was the cause of fractures in 79 patients (85%), and in 17 patients (15%) fractures occurred due to falls from height. Polytrauma was present in 31 patients (32%). According to the classification of Judet and Letournel, representation of acetabular fractures was as follows: posterior wall in 32 patients, posterior column in 28, anterior wall in 4, anterior column in 2, transverse fractures in 8, posterior wall and posterior column in 10, anterior and posterior wall in 6, both- column in 4 and transversal fracture and posterior wall in 2 patients. 14 patients were treated with traction, that is, 6 patients with femoral traction and 8 patients with both lateral and femoral traction. 82 patients (86.4%) were surgically treated. Kocher-Langenbeck approach was applied in the treatment of 78 patients. In two patients from the Kocher-Langenbeck’s approach, the Ollier’s approach had to be applied as well. Two acetabular were primarily treated with Ollier’s approach. Extended Smith- Peterson’s approach was applied 4 times, and Emile Letournel’s (ilioinguinal) approach 14 times. Results: Functional outcome (after follow-up of 18 months), according to the Harris hip score of surgical treatment in 82 patients, was as follows: good 46 (56%), satisfactory 32 (39%) and poor 4 (5%). Results of acetabulum fractures treated with traction were: good 8 (57%), satisfactory 4 (28%) and poor 2 (15%). According to the Brook’s classification of heterotopic

Does a cemented cage improve revision THA for severe acetabular defects?

PubMed

Hansen, Erik; Shearer, David; Ries, Michael D

2011-02-01

Evidence suggests a growing incidence of revision total hip arthroplasty (THA) including a subset with large acetabular defects. Revision THA for severe acetabular bone loss is associated with a relatively high rate of mechanical failure. We questioned whether cementing a cage to the reconstructed acetabular defect and pelvis would improve the rate of mechanical failure for patients with Type 3 defects (Paprosky et al.) with and without pelvic discontinuity in comparison to historical controls. We retrospectively collected data on 33 patients who underwent 35 revision THAs using an acetabular reconstruction cage cemented to morselized allograft and either structural allograft or trabecular metal augmentation for Type 3 defects in the presence (n = 13) and absence (n = 22) of pelvic discontinuity at a mean followup of 59 months (range, 24-92 months). The primary outcome was mechanical failure, defined as revision of the acetabular reconstruction for aseptic loosening. Revision surgery for mechanical failure occurred in four of the 13 patients with pelvic discontinuity and two of the 22 patients without discontinuity. Radiographic loosening occurred in one patient with and one patient without pelvic discontinuity. Seven of the 35 revisions were subsequently revised for deep infection all in patients who were immunocompromised. Cementing the cage to the pelvis can offer an advantage for treating severe acetabular defects. Trabecular metal augmentation appears to provide better initial mechanical stability than a structural allograft, but successful allograft reconstruction may restore bone stock. Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

[Use of the Omega plate for stabilisation of acetabular fractures: first experience].

PubMed

Šrám, J; Taller, S; Lukáš, R; Endrych, L

2013-01-01

The aim of our study is to solve the problem of insufficient fixation of comminuted fractures of the quadrilateral plane and the iliopectineal line. These fixation problems occur while using the standard narrow 3.5 mm fixation plate applied from a modified Stoppa approach. A new plate developed by the authors--the Omega plate--fulfils the requirements. In the period 2010-2012, we performed 156 stabilisations of pelvic ring fractures and acetabular fractures. We used the modified Stoppa approach applying the standard fixation plate in 24 patients and the Omega plate in 15 patients. The patient group with the Omega plate included 10 male and five female patients with the average age of 61 years (range, 30-72). Only 11 patients were followed up, with an average period of 13.3 months, because one patient was lost to followup and three patients were shortly after surgery. The surgical technique of Omega plate application is described in detail. The clinical evaluation of post-operative results was based on the Harris Hip Score; the graphical results were rated using the Matta and Pohlemann criteria. The Stoppa approach alone was used in four patients, combination of two approaches (Stoppa and Kocher-Langenbeck approach) was used in six cases and three approaches were employed in five patients. No adverse intra- or post-operative events were recorded. Excellent or satisfactory graphical results were obtained in 12 patients and an unsatisfactory graphical outcome was recorded in three cases. In the follow-up period ranging from 8 to 22 months, 11 patients healed. Late complications included avascular femoral head necrosis in two and severe post-traumatic coxarthrosis in three patients. Due to these complications, all five patients underwent total hip arthroplasty without previous Omega plate removal at an average interval of 15 months from the primary pelvic surgery. They were not included in the follow-up evaluation. The remaining six patients had an average Harris Hip

Computer assisted surgery in preoperative planning of acetabular fracture surgery: state of the art.

PubMed

Boudissa, Mehdi; Courvoisier, Aurélien; Chabanas, Matthieu; Tonetti, Jérôme

2018-01-01

The development of imaging modalities and computer technology provides a new approach in acetabular surgery. Areas covered: This review describes the role of computer-assisted surgery (CAS) in understanding of the fracture patterns, in the virtual preoperative planning of the surgery and in the use of custom-made plates in acetabular fractures with or without 3D printing technologies. A Pubmed internet research of the English literature of the last 20 years was carried out about studies concerning computer-assisted surgery in acetabular fractures. The several steps for CAS in acetabular fracture surgery are presented and commented by the main author regarding to his personal experience. Expert commentary: Computer-assisted surgery in acetabular fractures is still initial experiences with promising results. Patient-specific biomechanical models considering soft tissues should be developed to allow a more realistic planning.

Decreased Lumbar Lordosis and Deficient Acetabular Coverage Are Risk Factors for Subchondral Insufficiency Fracture.

PubMed

Jo, Woo Lam; Lee, Woo Suk; Chae, Dong Sik; Yang, Ick Hwan; Lee, Kyoung Min; Koo, Kyung Hoi

2016-10-01

Subchondral insufficiency fracture (SIF) of the femoral head occurs in the elderly and recipients of organ transplantation. Osteoporosis and deficient lateral coverage of the acetabulum are known risk factors for SIF. There has been no study about relation between spinopelvic alignment and anterior acetabular coverage with SIF. We therefore asked whether a decrease of lumbar lordosis and a deficiency in the anterior acetabular coverage are risk factors. We investigated 37 patients with SIF. There were 33 women and 4 men, and their mean age was 71.5 years (59-85 years). These 37 patients were matched with 37 controls for gender, age, height, weight, body mass index and bone mineral density. We compared the lumbar lordosis, pelvic incidence, pelvic tilt, sacral slope, acetabular index, acetabular roof angle, acetabular head index, anterior center-edge angle and lateral center-edge angle. Lumbar lordosis, pelvic tilt, sacral slope, lateral center edge angle, anterior center edge angle, acetabular index and acetabular head index were significantly different between SIF group and control group. Lumbar lordosis (OR = 1.11), lateral center edge angle (OR = 1.30) and anterior center edge angle (OR = 1.27) had significant associations in multivariate analysis. Decreased lumbar lordosis and deficient anterior coverage of the acetabulum are risk factors for SIF as well as decreased lateral coverage of the acetabulum.

Intraoperative CT in the assessment of posterior wall acetabular fracture stability.

PubMed

Cunningham, Brian; Jackson, Kelly; Ortega, Gil

2014-04-01

Posterior wall acetabular fractures that involve 10% to 40% of the posterior wall may or may not require an open reduction and internal fixation. Dynamic stress examination of the acetabular fracture under fluoroscopy has been used as an intraoperative method to assess joint stability. The aim of this study was to demonstrate the value of intraoperative ISO computed tomography (CT) examination using the Siemens ISO-C imaging system (Siemens Corp, Malvern, Pennsylvania) in the assessment of posterior wall acetabular fracture stability during stress examination under anesthesia. In 5 posterior wall acetabular fractures, standard fluoroscopic images (including anteroposterior pelvis and Judet radiographs) with dynamic stress examinations were compared with the ISO-C CT imaging system to assess posterior wall fracture stability during stress examination. After review of standard intraoperative fluoroscopic images under dynamic stress examination, all 5 cases appeared to demonstrate posterior wall stability; however, when the intraoperative images from the ISO-C CT imaging system demonstrated that 1 case showed fracture instability of the posterior wall segment during stress examination, open reduction and internal fixation was performed. The use of intraoperative ISO CT imaging has shown an initial improvement in the surgeon's ability to assess the intraoperative stability of posterior wall acetabular fractures during stress examination when compared with standard fluoroscopic images. Copyright 2014, SLACK Incorporated.

Validity and reliability of the Paprosky acetabular defect classification.

PubMed

Yu, Raymond; Hofstaetter, Jochen G; Sullivan, Thomas; Costi, Kerry; Howie, Donald W; Solomon, Lucian B

2013-07-01

The Paprosky acetabular defect classification is widely used but has not been appropriately validated. Reliability of the Paprosky system has not been evaluated in combination with standardized techniques of measurement and scoring. This study evaluated the reliability, teachability, and validity of the Paprosky acetabular defect classification. Preoperative radiographs from a random sample of 83 patients undergoing 85 acetabular revisions were classified by four observers, and their classifications were compared with quantitative intraoperative measurements. Teachability of the classification scheme was tested by dividing the four observers into two groups. The observers in Group 1 underwent three teaching sessions; those in Group 2 underwent one session and the influence of teaching on the accuracy of their classifications was ascertained. Radiographic evaluation showed statistically significant relationships with intraoperative measurements of anterior, medial, and superior acetabular defect sizes. Interobserver reliability improved substantially after teaching and did not improve without it. The weighted kappa coefficient went from 0.56 at Occasion 1 to 0.79 after three teaching sessions in Group 1 observers, and from 0.49 to 0.65 after one teaching session in Group 2 observers. The Paprosky system is valid and shows good reliability when combined with standardized definitions of radiographic landmarks and a structured analysis. Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

The Transverse Acetabular Ligament as an Intraoperative Guide to Cup Abduction.

PubMed

Hiddema, Willem B; van der Merwe, Johan F; van der Merwe, Werner

2016-07-01

The success of a total hip arthroplasty relies on optimal acetabular cup placement to ensure mating of the femoral head and acetabular cup throughout all positions of the hip joint. Poor cup placement is associated with dislocation, impingement, microseparation, component loosening, and accelerated wear due to rim loading. This study examined a novel method of using the transverse acetabular ligament (TAL) to guide cup inclination during primary total hip arthroplasty. A descriptive study using 16 hips from 9 cadavers. A computer navigation system measured inclination and version of the acetabular component in 3 positions with the lower edge of cup: (1) flush with, (2) 5 mm proximal to, and (3) 5 mm distal to free border of the TAL. The median inclination angles were 44° in position (1), 30° in position (2), and 64° in position (3). The median anteversion angle for all positions was 19°. Cup inclination was acceptable when the lower edge of the cup was flush or within 5 mm proximal to the TAL. Copyright © 2016 Elsevier Inc. All rights reserved.

Numerical analysis on seismic behavior of reinforced concrete beam to concrete filled steel tubular column connections with ring-beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Yi., E-mail: zhaoyi091218@163.com; Xu, Li. Hua.

This paper presents numerical study of the seismic behavior of reinforced concrete beam to concrete filled steel tube column connections with ring-beam. The material stress-strain relations, element type and boundary condition are selected, which are consistent with actual situation. Then the seismic behavior of this type of joint are researched by ABAQUS, and finite element analyses are conducted under cyclic loading. Its parameters are discussed including thickness of steel tubular column wall, sectional dimension of the ring-beam and strength of the core concrete. The results show that the ultimate capacity of the connections is improved with sectional dimension of themore » ring-beam increased. In the meanwhile, the influence on skeleton curve of the joints is slight of which included thickness of steel tubular column wall and strength of the core concrete.« less

Sacroiliac joint dysfunction as a reason for the development of acetabular retroversion: a new theory.

PubMed

Cibulka, Michael T

2014-05-01

Acetabular retroversion has been recently implicated as an important factor in the development of femoral acetabular impingement and hip osteoarthritis. The proper function of the hip joint requires that the anatomic features of the acetabulum and femoral head complement one another. In acetabular retroversion, the alignment of the acetabulum is altered where it opens in a posterolaterally instead of anterior direction. Changes in acetabular orientation can occur with alterations in pelvic tilt (anterior/posterior), and pelvic rotation (left/right). An overlooked problem that alters pelvic tilt and rotation, often seen by physical therapists, is sacroiliac joint dysfunction. A unique feature that develops in patients with sacroiliac joint dysfunction (SIJD) is asymmetry between the left and right innominate bones that can alter pelvic tilt and rotation. This article puts forth a theory suggesting that acetabular retroversion may be produced by sacroiliac joint dysfunction.

Is anatomic acetabular orientation related to pelvic morphology? CT analysis of 150 healthy pelvises.

PubMed

Sautet, P; Giorgi, H; Chabrand, P; Tropiano, P; Argenson, J-N; Parratte, S; Blondel, B

2018-05-01

Links between sagittal spinal alignment and acetabular orientation attract considerable research attention with the goal of optimising prosthetic cup position. However, whether pelvic incidence (PI) is related to anatomic acetabular orientation remains unknown. We therefore conducted a radiological study with the following objectives: to look for correlations between PI and anatomic acetabular parameters; to describe the sacro-pubic angle (SPA), defined by fixed bony pelvic landmarks, and its relations with acetabular anteversion; and to determine whether anatomical parameters (PI and SPA) correlate with demographic characteristics. PI correlates with anatomical acetabular parameters. We conducted a computed tomography (CT) study of the pelvises of 150 patients free of degenerative disease. Three parameters were measured: anatomic acetabular orientation in the Lewinnek reference plane, PI, and the SPA subtended by the line connecting the midpoint of the sacral endplate to the pubic symphysis and the anterior pelvic plane. Statistical tests were performed to look for correlations among these parameters. Intra-observer and inter-observer reproducibility was considered highly satisfactory (inter-class correlation coefficient, >86% and >82%, respectively). Mean PI was 58.6°±10.2° (range, 32.8°-97.6°), with no significant differences between genders or across age groups. Mean SPA was 34.7°±5.5° (range, 18.3°-49.8°). Mean anatomic acetabular anteversion (AAA) was greater in females (23.4°; range, 11.5°-34.5°) than in males (20°; range, 7.5°-34.5°) (P<0.001). PI did not correlate with any of the acetabular parameters (PI/AAA, r=0.8 and P=0.33; PI/acetabular inclination on the horizontal, r=-0.96 and P=0.24). SPA correlated significantly with both PI (r=0.33 and P<0.001) and AAA (r=0.33 and P<0.001). This CT study of normal pelvises showed that AAA was significantly greater in females and that SPA correlated significantly with both PI and acetabular

Acetabular cartilage defects cause altered hip and knee joint coordination variability during gait.

PubMed

Samaan, Michael A; Teng, Hsiang-Ling; Kumar, Deepak; Lee, Sonia; Link, Thomas M; Majumdar, Sharmila; Souza, Richard B

2015-12-01

Patients with acetabular cartilage defects reported increased pain and disability compared to those without acetabular cartilage defects. The specific effects of acetabular cartilage defects on lower extremity coordination patterns are unclear. The purpose of this study was to determine hip and knee joint coordination variability during gait in those with and without acetabular cartilage defects. A combined approach, consisting of a semi-quantitative MRI-based quantification method and vector coding, was used to assess hip and knee joint coordination variability during gait in those with and without acetabular cartilage lesions. The coordination variability of the hip flexion-extension/knee rotation, hip abduction-adduction/knee rotation, and hip rotation/knee rotation joint couplings were reduced in the acetabular lesion group compared to the control group during loading response of the gait cycle. The lesion group demonstrated increased variability in the hip flexion-extension/knee rotation and hip abduction-adduction/knee rotation joint couplings, compared to the control group, during the terminal stance/pre-swing phase of gait. Reduced variability during loading response in the lesion group may suggest reduced movement strategies and a possible compensation mechanism for lower extremity instability during this phase of the gait cycle. During terminal stance/pre-swing, a larger variability in the lesion group may suggest increased movement strategies and represent a compensation or pain avoidance mechanism caused by the load applied to the hip joint. Copyright © 2015 Elsevier Ltd. All rights reserved.

Magnetic resonance imaging with gadolinium arthrography to assess acetabular cartilage delamination.

PubMed

Zaragoza, Edward; Lattanzio, Pierre-Jean; Beaule, Paul E

2009-01-01

Recent reports have demonstrated magnetic resonance imaging (MRI) as a promising technique in detecting articular cartilage lesions of the hip joint. The purpose of our study was to evaluate the diagnostic performance of MRI with gadolinium arthrography in detecting acetabular cartilage delamination in patients with pre-arthritic hip pain. 46 patients (48 hips) underwent surgical dislocation of the hip. Mean age was 38.8 (range 17-56). There were 26 males and 20 females. All patients had Magnetic Resonance Imaging with gadolinium arthrography (MRA) before undergoing open hip surgery where the acetabular cartilage was inspected. Acetabular cartilage delamination on MRA was seen on sagittal images as a linear intra-articular filling defect of low signal intensity >1mm in thickness on T1 weighted images and surrounded by contrast. On MRA all hips had a labral tear confirmed at surgery. At surgery 30 hips had evidence of acetabular cartilage delamination, 4 hips had ulceration and 14 had no articular cartilage damage. The majority of labral tears and cartilage damage were located in the antero-superior quadrant. The sensitivity and specificity of MRA detection of cartilage delamination confirmed at surgery were 97% and 84%, respectively. The positive and negative predictive values of the MRA finding were 90% and 94%, respectively. The presence of the acetabular cartilage delamination represents an early stage of articular cartilage degeneration. When evaluating a young adult with hip pain, labral tears in association with cartilage delamination should be considered. MRA represents an effective diagnostic tool.

Design and fabrication of a boron reinforced intertank skirt

NASA Technical Reports Server (NTRS)

Henshaw, J.; Roy, P. A.; Pylypetz, P.

1974-01-01

Analytical and experimental studies were performed to evaluate the structural efficiency of a boron reinforced shell, where the medium of reinforcement consists of hollow aluminum extrusions infiltrated with boron epoxy. Studies were completed for the design of a one-half scale minimum weight shell using boron reinforced stringers and boron reinforced rings. Parametric and iterative studies were completed for the design of minimum weight stringers, rings, shells without rings and shells with rings. Computer studies were completed for the final evaluation of a minimum weight shell using highly buckled minimum gage skin. The detail design is described of a practical minimum weight test shell which demonstrates a weight savings of 30% as compared to an all aluminum longitudinal stiffened shell. Sub-element tests were conducted on representative segments of the compression surface at maximum stress and also on segments of the load transfer joint. A 10 foot long, 77 inch diameter shell was fabricated from the design and delivered for further testing.

Comparative study of comminuted posterior acetabular wall fracture treated with the Acetabular Tridimensional Memory Fixation System.

PubMed

Zhang, Yuntong; Zhao, Xue; Tang, Yang; Zhang, Chuncai; Xu, Shuogui; Xie, Yang

2014-04-01

Posterior wall fractures are one of the most common acetabular fractures. However, only 30% of these fractures involve a single large fragment, and comminuted acetabular posterior wall fractures pose a particular surgical challenge. The purpose of this study was to compare outcomes between patients who received fixation for comminuted posterior wall fracture using the Acetabular Tridimensional Memory Fixation System (ATMFS) and patients who underwent fixation with conventional screws and buttress plates (Plates group). Between April 2003 and May 2007, 196 consecutive patients who sustained a comminuted posterior wall fracture of acetabulum were treated with ATMFS or conventional screws and buttress plates. Operative time, fluoroscopy time, blood loss, and any intra-operative complications were recorded. Plain AP and lateral radiographs were obtained at all visits (Matta's criteria). Modified Merle d' Aubigne-Postel score, and Mos SF-36 score were compared between groups. Fifty patients were included in the analysis with 26 in the ATMFS group and 24 in the Plates group. The mean follow-up time was 57.5 months, ranging from 31 to 69 months. All patients had fully healed fractures at the final follow-up. There was no difference in clinical outcomes or radiological evaluations between groups. Patients with comminuted posterior wall fractures of the acetabulum treated with the ATMFS or conventional screws and buttress plate techniques achieve a good surgical result. Both techniques are safe, reliable, and practical. Use of the ATMFS technique may reduce blood loss and improve rigid support to marginal bone impaction. The use ATMFS may need additional support when fractures involve the superior roof. Copyright © 2013 Elsevier Ltd. All rights reserved.

Cement-in-cement acetabular revision with a constrained tripolar component.

PubMed

Leonidou, Andreas; Pagkalos, Joseph; Luscombe, Jonathan

2012-02-17

Dislocation of a total hip replacement (THR) is common following total hip arthroplasty (THA). When nonoperative management fails to maintain reduction, revision surgery is considered. The use of constrained acetabular liners has been extensively described. Complete removal of the old cement mantle during revision THA can be challenging and is associated with significant complications. Cement-in-cement revision is an established technique. However, the available clinical and experimental studies focus on femoral stem revision. The purpose of this study was to present a case of cement-in-cement acetabular revision with a constrained component for recurrent dislocations and to investigate the current best evidence for this technique. This article describes the case of a 74-year-old woman who underwent revision of a Charnley THR for recurrent low-energy dislocations. A tripolar constrained acetabular component was cemented over the primary cement mantle following removal of the original liner by reaming, roughening the surface, and thoroughly irrigating and drying the primary cement. Clinical and radiological results were good, with the Oxford Hip Score improving from 11 preoperatively to 24 at 6 months postoperatively. The good short-term results of this case and the current clinical and biomechanical data encourage the use of the cement-in-cement technique for acetabular revision. Careful irrigation, drying, and roughening of the primary surface are necessary. Copyright 2012, SLACK Incorporated.

Pelvic incidence: a predictive factor for three-dimensional acetabular orientation-a preliminary study.

PubMed

Boulay, Christophe; Bollini, Gérard; Legaye, Jean; Tardieu, Christine; Prat-Pradal, Dominique; Chabrol, Brigitte; Jouve, Jean-Luc; Duval-Beaupère, Ginette; Pélissier, Jacques

2014-01-01

Acetabular cup orientation (inclination and anteversion) is a fundamental topic in orthopaedics and depends on pelvis tilt (positional parameter) emphasising the notion of a safe range of pelvis tilt. The hypothesis was that pelvic incidence (morphologic parameter) could yield a more accurate and reliable assessment than pelvis tilt. The aim was to find out a predictive equation of acetabular 3D orientation parameters which were determined by pelvic incidence to include in the model. The second aim was to consider the asymmetry between the right and left acetabulae. Twelve pelvic anatomic specimens were measured with an electromagnetic Fastrak system (Polhemus Society) providing 3D position of anatomical landmarks to allow measurement of acetabular and pelvic parameters. Acetabulum and pelvis data were correlated by a Spearman matrix. A robust linear regression analysis provided prediction of acetabulum axes. The orientation of each acetabulum could be predicted by the incidence. The incidence is correlated with the morphology of acetabula. The asymmetry of the acetabular roof was correlated with pelvic incidence. This study allowed analysis of relationships of acetabular orientation and pelvic incidence. Pelvic incidence (morphologic parameter) could determine the safe range of pelvis tilt (positional parameter) for an individual and not a group.

Pelvic Incidence: A Predictive Factor for Three-Dimensional Acetabular Orientation—A Preliminary Study

PubMed Central

Bollini, Gérard; Legaye, Jean; Tardieu, Christine; Prat-Pradal, Dominique; Chabrol, Brigitte; Jouve, Jean-Luc; Duval-Beaupère, Ginette; Pélissier, Jacques

2014-01-01

Acetabular cup orientation (inclination and anteversion) is a fundamental topic in orthopaedics and depends on pelvis tilt (positional parameter) emphasising the notion of a safe range of pelvis tilt. The hypothesis was that pelvic incidence (morphologic parameter) could yield a more accurate and reliable assessment than pelvis tilt. The aim was to find out a predictive equation of acetabular 3D orientation parameters which were determined by pelvic incidence to include in the model. The second aim was to consider the asymmetry between the right and left acetabulae. Twelve pelvic anatomic specimens were measured with an electromagnetic Fastrak system (Polhemus Society) providing 3D position of anatomical landmarks to allow measurement of acetabular and pelvic parameters. Acetabulum and pelvis data were correlated by a Spearman matrix. A robust linear regression analysis provided prediction of acetabulum axes. The orientation of each acetabulum could be predicted by the incidence. The incidence is correlated with the morphology of acetabula. The asymmetry of the acetabular roof was correlated with pelvic incidence. This study allowed analysis of relationships of acetabular orientation and pelvic incidence. Pelvic incidence (morphologic parameter) could determine the safe range of pelvis tilt (positional parameter) for an individual and not a group. PMID:25006461

Acetabular rim and surface segmentation for hip surgery planning and dysplasia evaluation

NASA Astrophysics Data System (ADS)

Tan, Sovira; Yao, Jianhua; Yao, Lawrence; Summers, Ronald M.; Ward, Michael M.

2008-03-01

Knowledge of the acetabular rim and surface can be invaluable for hip surgery planning and dysplasia evaluation. The acetabular rim can also be used as a landmark for registration purposes. At the present time acetabular features are mostly extracted manually at great cost of time and human labor. Using a recent level set algorithm that can evolve on the surface of a 3D object represented by a triangular mesh we automatically extracted rims and surfaces of acetabulae. The level set is guided by curvature features on the mesh. It can segment portions of a surface that are bounded by a line of extremal curvature (ridgeline or crestline). The rim of the acetabulum is such an extremal curvature line. Our material consists of eight hemi-pelvis surfaces. The algorithm is initiated by putting a small circle (level set seed) at the center of the acetabular surface. Because this surface distinctively has the form of a cup we were able to use the Shape Index feature to automatically extract an approximate center. The circle then expands and deforms so as to take the shape of the acetabular rim. The results were visually inspected. Only minor errors were detected. The algorithm also proved to be robust. Seed placement was satisfactory for the eight hemi-pelvis surfaces without changing any parameters. For the level set evolution we were able to use a single set of parameters for seven out of eight surfaces.

Arthroscopic treatment of femoral nerve paresthesia caused by an acetabular paralabral cyst.

PubMed

Kanauchi, Taira; Suganuma, Jun; Mochizuki, Ryuta; Uchikawa, Shinichi

2014-05-01

This report describes a rare case of femoral nerve paresthesia caused by an acetabular paralabral cyst of the hip joint. A 68-year-old woman presented with a 6-month history of right hip pain and paresthesia along the anterior thigh and radiating down to the anterior aspect of the knee. Radiography showed osteoarthritis with a narrowed joint space in the right hip joint. Magnetic resonance imaging showed a cyst with low T1- and high T2-weighted signal intensity arising from a labral tear at the anterior aspect of the acetabulum. The cyst was connected to the joint space and displaced the femoral nerve to the anteromedial side. The lesion was diagnosed as an acetabular paralabral cyst causing femoral neuropathy. Because the main symptom was femoral nerve paresthesia and the patient desired a less invasive procedure, arthroscopic labral repair was performed to stop synovial fluid flow to the paralabral cyst that was causing the femoral nerve paresthesia. After surgery, the cyst and femoral nerve paresthesia disappeared. At the 18-month follow-up, the patient had no recurrence. There have been several reports of neurovascular compression caused by the cyst around the hip joint. To the authors' knowledge, only 3 cases of acetabular paralabral cysts causing sciatica have been reported. The current patient appears to represent a rare case of an acetabular paralabral cyst causing femoral nerve paresthesia. The authors suggest that arthroscopic labral repair for an acetabular paralabral cyst causing neuropathy can be an option for patients who desire a less invasive procedure. Copyright 2014, SLACK Incorporated.

The effect of acetabular cup size on the short-term stability of revision hip arthroplasty: a finite element investigation.

PubMed

Phillips, A T M; Pankaj; Usmani, A S; Howie, C R

2004-01-01

The study uses idealized two-dimensional finite element models to examine the behaviour of the acetabular construct following revision hip arthroplasty, carried out using the Slooff-Ling impaction grafting technique. The behaviour of bone graft was considered in detail, with non-linear elasticity and non-associated plasticity being adopted. Load was applied to the acetabular construct through a femoral head using smooth sliding surfaces. In particular, four models were subjected to two idealized cyclic load cases to investigate the effect of acetabular cup size on the short-term stability of the acetabular construct. The study suggests that benefits may be gained by using the largest practical size of acetabular cup.

High-precision measurements of cementless acetabular components using model-based RSA: an experimental study.

PubMed

Baad-Hansen, Thomas; Kold, Søren; Kaptein, Bart L; Søballe, Kjeld

2007-08-01

In RSA, tantalum markers attached to metal-backed acetabular cups are often difficult to detect on stereo radiographs due to the high density of the metal shell. This results in occlusion of the prosthesis markers and may lead to inconclusive migration results. Within the last few years, new software systems have been developed to solve this problem. We compared the precision of 3 RSA systems in migration analysis of the acetabular component. A hemispherical and a non-hemispherical acetabular component were mounted in a phantom. Both acetabular components underwent migration analyses with 3 different RSA systems: conventional RSA using tantalum markers, an RSA system using a hemispherical cup algorithm, and a novel model-based RSA system. We found narrow confidence intervals, indicating high precision of the conventional marker system and model-based RSA with regard to migration and rotation. The confidence intervals of conventional RSA and model-based RSA were narrower than those of the hemispherical cup algorithm-based system regarding cup migration and rotation. The model-based RSA software combines the precision of the conventional RSA software with the convenience of the hemispherical cup algorithm-based system. Based on our findings, we believe that these new tools offer an improvement in the measurement of acetabular component migration.

Is labral hypotrophy correlated with increased acetabular depth?

PubMed Central

Toft, Felix; Anliker, Elmar; Beck, Martin

2015-01-01

Labral hypertrophy is a distinct feature in hip dysplasia. Occasionally, very small, hypotrophic labra are observed. However, there is no literature concerning this pathology. We investigated if the size of the labrum correlated with any radiologic parameters reflecting the amount of acetabular coverage. It was hypothezised that there is a negative correlation between labrum size and acetabular coverage. Labra were categorized into three groups depending on the relation between length of the articular sided surface and height of bony attachment. Labra with a height:length ratio of 2 were classified as hypotrophic, with a height:length ratio of 1 as normal and with a ratio of 0.5 as hypertrophic. Labral cross-sectional areas (CSA) were measured on radial magnetic resonance imaging-arthrography slices using the measuring tool of the PACS system of 20 hips with hypotrophic labra (group 1), 20 hips with normal labral appearance (group 2) and 10 hips with hypertrophic labra (group 3). These values were then analyzed against following parameters: neck-shaft-angle (NSA), lateral center-edge angle (LCE), acetabular index (AI), femoral extrusion index (FEI) and acetabular retroversion index (ARI). Analyses of variance were used to determine differences in mean values between the three groups. Mean labral CSA differed significantly between all groups (group 1: 12.1 ± 2.9 mm2; group 2: 25.2 ± 6.2 mm2; group 3: 41.1 ± 12.3 mm2; P < 0.001). NSA, LCE, AI and FEI all showed a significant difference between group 3 and 1 or 2. The ARI showed no difference between groups. Stepwise linear regression analyses showed a significant correlation between LCE angle and labral CSA with a corrected R2-value of 0.301. Labral CSA correlates with the LCE. No statistically significant difference between groups 1 and 2 concerning the LCE, AI or FEI could be identified. Nevertheless, group 1 had the highest mean coverage of all groups, hips with hypertrophic labra

The prevalence of acetabular anomalies associated with pistol-grip-deformity in osteoarthritic hips.

PubMed

Ipach, I; Mittag, F; Walter, C; Syha, R; Wolf, P; Kluba, T

2013-02-01

Acetabular retroversion, excessive acetabular coverage and abnormal head-neck-junction with a so-called "pistol-grip-deformity" were added to the classical description of hip dysplasia to describe pathological hip morphology. The aim of the current study was the detection of pathological acetabular geometry in patients with an abnormal head-neck-junction. Femoroacetabular impingement and hip dysplasia features are frequent in patients with end-stage osteoarthritis before 60 years of age. We analysed our data bank retrospectively for all patients who received a Total Hip Arthroplasty (THA) due to end-stage osteoarthritis before the age of 60 years. The pelvic-views and the Dunn-view of these patients were screened for an abnormal head-neck-junction by measuring the head-ratio and the alpha-angle. An orthopaedic surgeon and a radiologist did this independently. These radiographies were measured for signs of acetabular dysplasia, excessive acetabular coverage and crossing sign. A consecutive series of 135 total hip arthroplasties were performed in patients aged less or equal to 60 years because of end-stage osteoarthritis. From these, 81 patients were classified as having an abnormal head-neck-junction. The mean head-ratio in these 81 patients was 1.52±0.35, the mean alpha-angle was 62.5°±9.3°. The mean CE-angle of these 81 patients was 35.8°±10.4°, the mean CA-angle was 36.7°±5.7°, the mean depth-width ratio was 49.1±10, the mean extrusion index was 19.1±9.2 and the mean CCD-angle was 131.7°±7.3°. Of these 81hips, 14 had isolated pistol-grip-deformity, while 11 hips had associated dysplasia, 38 had excessive acetabular coverage, and 14 had crossing sign. In addition, a crossing sign was identified in four of the 11 dysplastic hips and 19 of the 38 of the hips having excessive acetabular coverage. There was no statistically significant difference in regard to the age between the four groups (P=0.087). In contrast, the hips that had excessive acetabular

Cemented total hip replacement cable debris and acetabular construct durability.

PubMed

Altenburg, Aaron J; Callaghan, John J; Yehyawi, Tameem M; Pedersen, Douglas R; Liu, Steve S; Leinen, Jessica A; Dahl, Kevin A; Goetz, Devon D; Brown, Thomas D; Johnston, Richard C

2009-07-01

Third-body wear can adversely affect the outcome of total hip arthroplasty by causing increased polyethylene wear, osteolysis, and component loosening. We hypothesized that there would be greater generation and migration of metal debris to the bearing surfaces in hips in which cobalt-chromium cables were used to reattach the osteotomized greater trochanter when compared with hips in which stainless steel wires were used. Between June 1981 and December 1983, 196 consecutive total hip arthroplasties were performed with use of an Iowa stem and a titanium-backed cemented acetabular component, with cobalt-chromium cable trochanteric reattachment. After nineteen to twenty years of follow-up, the patients were evaluated with regard to the depth of head penetration into the polyethylene (as a surrogate for wear), osteolysis, loosening, and the need for revision. The results were compared with those for a series of 304 total hip arthroplasties that were performed by the same surgeon from January 1984 to December 1985 with use of the same components and the same surgical technique, but with stainless steel wire trochanteric reattachment. The two groups had a comparable nineteen to twenty-year follow-up. All living patients (fifty-nine hips in the cable group and ninety-two hips in the wire group) had minimum ten-year follow-up radiographs. The polyethylene wear rate was 0.101 mm/yr for the cable group and 0.082 mm/yr for the wire group (p = 0.039). For the living patients, the rate of revision of the acetabular component because of aseptic loosening was 37.3% (twenty-two hips) for the cable group and 20.7% (nineteen hips) for the wire group (p = 0.025). The rate of acetabular osteolysis was 44% (twenty-six hips) for the cable group and 26% (twenty-four hips) for the wire group (p = 0.022). Kaplan-Meier analysis with revision of the acetabular component because of aseptic loosening as the end point demonstrated survival rates of 73.7% +/- 9% and 83% +/- 7% for the cable and

Nuclear reactor containment structure with continuous ring tunnel at grade

DOEpatents

Seidensticker, Ralph W.; Knawa, Robert L.; Cerutti, Bernard C.; Snyder, Charles R.; Husen, William C.; Coyer, Robert G.

1977-01-01

A nuclear reactor containment structure which includes a reinforced concrete shell, a hemispherical top dome, a steel liner, and a reinforced-concrete base slab supporting the concrete shell is constructed with a substantial proportion thereof below grade in an excavation made in solid rock with the concrete poured in contact with the rock and also includes a continuous, hollow, reinforced-concrete ring tunnel surrounding the concrete shell with its top at grade level, with one wall integral with the reinforced concrete shell, and with at least the base of the ring tunnel poured in contact with the rock.

Optimal acetabular component orientation estimated using edge-loading and impingement risk in patients with metal-on-metal hip resurfacing arthroplasty.

PubMed

Mellon, Stephen J; Grammatopoulos, George; Andersen, Michael S; Pandit, Hemant G; Gill, Harinderjit S; Murray, David W

2015-01-21

Edge-loading in patients with metal-on-metal resurfaced hips can cause high serum metal ion levels, the development of soft-tissue reactions local to the joint called pseudotumours and ultimately, failure of the implant. Primary edge-loading is where contact between the femoral and acetabular components occurs at the edge/rim of the acetabular component whereas impingement of the femoral neck on the acetabular component's edge causes secondary or contrecoup edge-loading. Although the relationship between the orientation of the acetabular component and primary edge-loading has been identified, the contribution of acetabular component orientation to impingement and secondary edge-loading is less clear. Our aim was to estimate the optimal acetabular component orientation for 16 metal-on-metal hip resurfacing arthroplasty (MoMHRA) subjects with known serum metal ion levels. Data from motion analysis, subject-specific musculoskeletal modelling and Computed Tomography (CT) measurements were used to calculate the dynamic contact patch to rim (CPR) distance and impingement risk for 3416 different acetabular component orientations during gait, sit-to-stand, stair descent and static standing. For each subject, safe zones free from impingement and edge-loading (CPR <10%) were defined and, consequently, an optimal acetabular component orientation was determined (mean inclination 39.7° (SD 6.6°) mean anteversion 14.9° (SD 9.0°)). The results of this study suggest that the optimal acetabular component orientation can be determined from a patient's motion and anatomy. However, 'safe' zones of acetabular component orientation associated with reduced risk of dislocation and pseudotumour are also associated with a reduced risk of edge-loading and impingement. Copyright © 2014 Elsevier Ltd. All rights reserved.

Endoscopic resection of acetabular screw tip to decompress sciatic nerve following total hip arthroplasty.

PubMed

Yoon, Sun-Jung; Park, Myung-Sik; Matsuda, Dean K; Choi, Yun Ho

2018-06-04

Sciatic nerve injuries following total hip arthroplasty are disabling complications. Although degrees of injury are variable from neuropraxia to neurotmesis, mechanical irritation of sciatic nerve might be occurred by protruding hardware. This case shows endoscopic decompression for protruded acetabular screw irritating sciatic nerve, the techniques described herein may permit broader arthroscopic/endoscopic applications for management of complications after reconstructive hip surgery. An 80-year-old man complained of severe pain and paresthesias following acetabular component revision surgery. Physical findings included right buttock pain with radiating pain to lower extremity. Radiographs and computed tomography imaging showed that the sharp end of protruded screw invaded greater sciatic foramen anterior to posterior and distal to proximal direction at sciatic notch level. A protruding tip of the acetabular screw at the sciatic notch was decompressed by use of techniques gained from experience performing endoscopic sciatic nerve decompression. The pre-operative pain and paresthesias resolved post-operatively after recovering from anesthesia. This case report describes the first documented endoscopic resection of the tip of the acetabular screw irritating sciatic nerve after total hip arthroplasty. If endoscopic resection of an offending acetabular screw can be performed in a safe and minimally invasive manner, one can envision a future expansion of the role of hip arthroscopic surgery in several complications management after total hip arthroplasty.

The Morscher Press-Fit Acetabular Component: An Independent Long-Term Review at 18-22 Years.

PubMed

Gwynne-Jones, David P; Lash, Heath W R; James, Andrew W; Iosua, Ella E; Matheson, John A

2017-08-01

There are relatively few 20-year results of uncemented acetabular components, and most of these are modular designs. This study reports the 20-year results of a monoblock press-fit acetabular component. A total of 122 total hip arthroplasties (111 patients) using the Morscher cup were reviewed at a mean of 19.7 years. The average age at implantation was 57.3 years (range, 36-74 years), and 81 (66%) were men. Twenty-two patients (25 hips) had died. Seven hips were revised, including 5 acetabular revisions. Six patients (6 hips) declined to participate but were known not to have been revised. The mean Oxford hip score was 41.1 (range, 22-48), and the mean reduced Western Ontario and McMaster Universities Osteoarthritis Index score was 5.7/48 (range, 0-24). Eccentric wear was seen in 13 (15.7%) and major osteolysis in 14 (17%) of 82 surviving hips with radiographs. The all-cause revision rate was 0.32 per 100 observed component years (95% confidence interval [CI], 0.13-0.66). The 20-year Kaplan-Meier survival was 93.4% (CI, 86.6-96.8) for all-cause revisions, 95.5% (CI, 89.4-98.1) for any acetabular revision, and 97.1% (CI, 91.2-99.1) for acetabular aseptic loosening, wear, or osteolysis. The Morscher acetabular component has continued to perform well at 20 years despite using conventional polyethylene with results that match or surpass other cementless acetabulae. Copyright © 2017 Elsevier Inc. All rights reserved.

Biochemical and Cellular Assessment of Acetabular Chondral Flaps Identified During Hip Arthroscopy.

PubMed

Hariri, Sanaz; Truntzer, Jeremy; Smith, Robert Lane; Safran, Marc R

2015-06-01

To analyze chondral flaps debrided during hip arthroscopy to determine their biochemical and cellular composition. Thirty-one full-thickness acetabular chondral flaps were collected during hip arthroscopy. Biochemical analysis was undertaken in 21 flaps from 20 patients, and cellular viability was determined in 10 flaps from 10 patients. Biochemical analysis included concentrations of (1) DNA (an indicator of chondrocyte content), (2) hydroxyproline (an indicator of collagen content), and (3) glycosaminoglycan (an indicator of chondrocyte biosynthesis). Higher values for these parameters indicated more healthy tissue. The flaps were examined to determine the percentage of viable chondrocytes. The percentage of acetabular chondral flap specimens that had concentrations within 1 SD of the mean values reported in previous normal cartilage studies was 38% for DNA, 0% for glycosaminoglycan, and 43% for hydroxyproline. The average cellular viability of our acetabular chondral flap specimens was 39% (SD, 14%). Only 2 of the 10 specimens had more than half the cells still viable. There was no correlation between (1) the gross examination of the joint or knowledge of the patient's demographic characteristics and symptoms and (2) biochemical properties and cell viability of the flap, with one exception: a degenerative appearance of the surrounding cartilage correlated with a higher hydroxyproline concentration. Although full-thickness acetabular chondral flaps can appear normal grossly, the biochemical properties and percentage of live chondrocytes in full-thickness chondral flaps encountered in hip arthroscopy show that this tissue is not normal. There has been recent interest in repairing chondral flaps encountered during hip arthroscopy. These data suggest that acetabular chondral flaps are not biochemically and cellularly normal. Although these flaps may still be valuable mechanically and/or as a scaffold in some conductive or inductive capacity, further study is

The boiled-egg technique: a new method for obtaining femoral head autograft used in acetabular defect reconstruction.

PubMed

Bucknall, Vittoria; Mehdi, Ali

2013-09-01

Primary total hip arthroplasty can be complicated by acetabular bony defects, threatening the biomechanical integrity of the prosthesis. Traditionally, when autologous bone is used to pack these defects, it is obtained from thin slices of femoral head in addition to acetabular reamings. We report a novel technique for the acquisition of autologous femoral head bone graft used in the reconstruction of acetabular defects during primary total hip arthroplasty. Copyright © 2013 Elsevier Inc. All rights reserved.

Impaction grafted bone chip size effect on initial stability in an acetabular model: Mechanical evaluation.

PubMed

Holton, Colin; Bobak, Peter; Wilcox, Ruth; Jin, Zhongmin

2013-01-01

Acetabular bone defect reconstruction is an increasing problem for surgeons with patients undergoing complex primary or revision total hip replacement surgery. Impaction bone grafting is one technique that has favourable long-term clinical outcome results for patients who undergo this reconstruction method for acetabular bone defects. Creating initial mechanical stability of the impaction bone graft in this technique is known to be the key factor in achieving a favourable implant survival rate. Different sizes of bone chips were used in this technique to investigate if the size of bone chips used affected initial mechanical stability of a reconstructed acetabulum. Twenty acetabular models were created in total. Five control models were created with a cemented cup in a normal acetabulum. Then five models in three different groups of bone chip size were constructed. The three groups had an acetabular protrusion defect reconstructed using either; 2-4 mm(3), 10 mm(3) or 20 mm(3) bone chip size for impaction grafting reconstruction. The models underwent compression loading up to 9500 N and displacement within the acetabular model was measured indicating the initial mechanical stability. This study reveals that, although not statistically significant, the largest (20 mm(3)) bone chip size grafted models have an inferior maximum stiffness compared to the medium (10 mm(3)) bone chip size. Our study suggests that 10 mm(3) size of bone chips provide better initial mechanical stability compared to smaller or larger bone chips. We dismissed the previously held opinion that the biggest practically possible graft is best for acetabular bone graft impaction.

Cemented Total Hip Replacement Cable Debris and Acetabular Construct Durability

PubMed Central

Altenburg, Aaron J.; Callaghan, John J.; Yehyawi, Tameem M.; Pedersen, Douglas R.; Liu, Steve S.; Leinen, Jessica A.; Dahl, Kevin A.; Goetz, Devon D.; Brown, Thomas D.; Johnston, Richard C.

2009-01-01

Background: Third-body wear can adversely affect the outcome of total hip arthroplasty by causing increased polyethylene wear, osteolysis, and component loosening. We hypothesized that there would be greater generation and migration of metal debris to the bearing surfaces in hips in which cobalt-chromium cables were used to reattach the osteotomized greater trochanter when compared with hips in which stainless steel wires were used. Methods: Between June 1981 and December 1983, 196 consecutive total hip arthroplasties were performed with use of an Iowa stem and a titanium-backed cemented acetabular component, with cobalt-chromium cable trochanteric reattachment. After nineteen to twenty years of follow-up, the patients were evaluated with regard to the depth of head penetration into the polyethylene (as a surrogate for wear), osteolysis, loosening, and the need for revision. The results were compared with those for a series of 304 total hip arthroplasties that were performed by the same surgeon from January 1984 to December 1985 with use of the same components and the same surgical technique, but with stainless steel wire trochanteric reattachment. The two groups had a comparable nineteen to twenty-year follow-up. All living patients (fifty-nine hips in the cable group and ninety-two hips in the wire group) had minimum ten-year follow-up radiographs. Results: The polyethylene wear rate was 0.101 mm/yr for the cable group and 0.082 mm/yr for the wire group (p = 0.039). For the living patients, the rate of revision of the acetabular component because of aseptic loosening was 37.3% (twenty-two hips) for the cable group and 20.7% (nineteen hips) for the wire group (p = 0.025). The rate of acetabular osteolysis was 44% (twenty-six hips) for the cable group and 26% (twenty-four hips) for the wire group (p = 0.022). Kaplan-Meier analysis with revision of the acetabular component because of aseptic loosening as the end point demonstrated survival rates of 73.7% ± 9% and

Acetabular overcoverage in the horizontal plane: an underdiagnosed trigger of early hip arthritis. A CT scan study in young adults.

PubMed

Valera, Màrius; Ibáñez, Natalia; Sancho, Rogelio; Llauger, Jaume; Gich, Ignasi

2018-01-01

Acetabular overcoverage promotes hip osteoarthritis causing a pincer-type femoroacetabular impingement. Acetabular coverage in the horizontal plane is usually poorly defined in imaging studies and may be misdiagnosed. The goal of this study was to analyze the role of acetabular overcoverage measured in the frontal plane and in the horizontal plane by CT scan and to determine its relationship with other anatomic features in the onset of hip arthritis in young adults. We compared prospectively CT scans from two groups of adults of 55 years or younger: the patient group (n = 30) consisted of subjects with diagnosis of early hip arthritis (Tönnis Grade I or II) and the control group (n = 31) consisted of subjects with healthy hips. Two independent observers analyzed centre edge angle (CEA), acetabular anteversion angle (AAA), anterior sector acetabular angle (AASA), posterior sector acetabular angle (PASA), horizontal acetabular sector angle (HASA), femoral anteversion angle (FAVA), alpha angle (AA), and Mckibbin Instability Index (MI). Angles measuring the acetabular coverage on the horizontal plane (AASA, PASA and, HASA) were significantly higher in the patient group (p < 0.001, p = 0.03 and p < 0.001, respectively). Pearson's correlation coefficient showed a positive correlation between CEA and HASA in patients (r = 0.628) and in controls (r = 0.660). However, a high CEA (> 35º) was strongly associated with a high HASA (> 160º) in patients (p = 0.024) but not in controls (p = 0.21), suggesting that pincer should be simultaneously present in the horizontal and frontal plane to trigger hip degeneration. No significant association was detected between a high alpha angle (> 60º) and a high CEA (> 35º suggesting that a mixed pincer-cam aetiology was not prevalent in our series. Multivariate regression analysis showed the most significant predictors of degenerative joint disease were HASA (p = 0.008), AA (p = 0.048) and ASAA (p = 0

Improving the accuracy of acetabular cup implantation using a bulls-eye spirit level.

PubMed

Macdonald, Duncan; Gupta, Sanjay; Ohly, Nicholas E; Patil, Sanjeev; Meek, R; Mohammed, Aslam

2011-01-01

Acetabular introducers have a built-in inclination of 45 degrees to the handle shaft. With patients in the lateral position, surgeons aim to align the introducer shaft vertical to the floor to implant the acetabulum at 45 degrees. We aimed to determine if a bulls-eye spirit level attached to an introducer improved the accuracy of implantation. A small circular bulls-eye spirit level was attached to the handle of an acetabular introducer. A saw bone hemipelvis was fixed to a horizontal, flat surface. A cement substitute was placed in the acetabulum and subjects were asked to implant a polyethylene cup, aiming to obtain an angle of inclination of 45 degrees. Two attempts were made with the spirit level masked and two with it unmasked. The distance of the air bubble from the spirit level's center was recorded by a single assessor. The angle of inclination of the acetabular component was then calculated. Subjects included both orthopedic consultants and trainees. Twenty-five subjects completed the study. Accuracy of acetabular implantation when using the unmasked spirit level improved significantly in all grades of surgeon. With the spirit level masked, 12 out of 50 attempts were accurate at 45 degrees inclination; 11 out of 50 attempts were "open," with greater than 45 degrees of inclination, and 27 were "closed," with less than 45 degrees. With the spirit level visible, all subjects achieved an inclination angle of exactly 45 degrees. A simple device attached to the handle of an acetabular introducer can significantly improve the accuracy of implantation of a cemented cup into a saw bone pelvis in the lateral position.

Pelvic Incidence and Acetabular Version in Slipped Capital Femoral Epiphysis.

PubMed

Gebhart, Jeremy J; Bohl, Michael S; Weinberg, Douglas S; Cooperman, Daniel R; Liu, Raymond W

2015-09-01

The etiology of slipped capital femoral epiphysis (SCFE) is multifactorial, but the role of sagittal balance of the pelvis as a contributing factor to its development has not been well studied. Our primary purpose was to determine whether a smaller pelvic incidence (PI), a position-independent anatomic parameter that regulates pelvic orientation, could be a factor that increases shear stress in the epiphyseal growth plate and potentially contributes to the development of SCFE. We also set out to determine whether acetabular retroversion was associated with SCFE. We obtained 14 cadaveric pelvi from the Hamann-Todd Osteological Collection whose femurs showed evidence of post-SCFE deformity. Two hundred age-matched, sex-matched, and race-matched pelvi were used as controls. PI and acetabular version were measured using standardized lateral photographs and goniometers, respectively. T tests were performed to evaluate for differences in measured parameters between groups. The mean PI was 40.6±6.1 degrees for SCFE specimens and 47.4±9.9 degrees for normal specimens (P=0.01). The mean version of SCFE and normal acetabula was 15±7 and 17±6 degrees, respectively (P=0.39). There was also no significant difference in version between SCFE acetabula and the contralateral, uninvolved acetabular of the same specimen (15±7 vs. 17±8 degrees, P=0.33). Specimens with SCFE deformity demonstrated a smaller PI than a large cohort of normal control specimens. We found no significant difference between acetabular version of specimens with and without SCFE deformity. Contralateral or unaffected acetabuli of SCFE specimens were not more retroverted than the affected side of the same specimen. Sagittal balance of the pelvis, and particularly decreased PI, may play an important role in the development of SCFE. The influence of mechanical factors beyond the hip joint in the development of SCFE should be considered by clinicians.

Does Increased Coefficient of Friction of Highly Porous Metal Increase Initial Stability at the Acetabular Interface?

PubMed

Goldman, Ashton H; Armstrong, Lucas C; Owen, John R; Wayne, Jennifer S; Jiranek, William A

2016-03-01

Highly porous metal acetabular components illustrate a decreased rate of aseptic loosening in short-term follow-up compared with previous registry data. This study compared the effect of component surface roughness at the bone-implant interface and the quality of the bone on initial pressfit stability. The null hypothesis is that a standard porous coated acetabular cup would show no difference in initial stability as compared with a highly porous acetabular cup when subjected to a bending moment. Second, would bone mineral density (BMD) be a significant variable under these test conditions. In a cadaveric model, acetabular cup micromotion was measured during a 1-time cantilever bending moment applied to 2 generations of pressfit acetabular components. BMD data were also obtained from the femoral necks available for associated specimen. The mean bending moment at 150 μm was not found to be significantly different for Gription (24.6 ± 14.0 N m) cups vs Porocoat (25 ± 10.2 N m; P > .84). The peak bending moment tolerated by Gription cups (33.9 ± 20.3 N m) was not found to be significantly different from Porocoat (33.5 ± 12.2 N m; P > .92). No correlation between BMD and bending moment at 150 μm of displacement could be identified. The coefficient of friction provided by highly porous metal acetabular shells used in this study did not provide better resistance to migration under bending load when compared with a standard porous coated component. Copyright © 2016 Elsevier Inc. All rights reserved.

Arrangement for connecting a fiber-reinforced plastic pipe to a stainless steel flange

DOEpatents

Allais, Arnaud [D-30625 Hannover, DE; Hoffmann, Ernst [D-30855 Langenhagen, DE

2008-02-05

Arrangement for connecting a fiber-reinforced plastic pipe (18) to a stainless steel flange (12, 16), in which the end of the fiber-reinforced plastic pipe (18) is accommodated in a ring-shaped groove (12a, 16a) in the flange (12, 16), the groove conforming to the dimensions of the fiber-reinforced plastic pipe (18), where the gap remaining between the end of the fiber-reinforced plastic pipe (18) and the ring-shaped groove (12a, 16a) is filled with a sealant (19).

Analysis of acetabular orientation and femoral anteversion using images of three-dimensional reconstructed bone models.

PubMed

Park, Jaeyeong; Kim, Jun-Young; Kim, Hyun Deok; Kim, Young Cheol; Seo, Anna; Je, Minkyu; Mun, Jong Uk; Kim, Bia; Park, Il Hyung; Kim, Shin-Yoon

2017-05-01

Radiographic measurements using two-dimensional (2D) plain radiographs or planes from computed tomography (CT) scans have several drawbacks, while measurements using images of three-dimensional (3D) reconstructed bone models can provide more consistent anthropometric information. We compared the consistency of results using measurements based on images of 3D reconstructed bone models (3D measurements) with those using planes from CT scans (measurements using 2D slice images). Ninety-six of 561 patients who had undergone deep vein thrombosis-CT between January 2013 and November 2014 were randomly selected. We evaluated measurements using 2D slice images and 3D measurements. The images used for 3D reconstruction of bone models were obtained and measured using [Formula: see text] and [Formula: see text] (Materialize, Leuven, Belgium). The mean acetabular inclination, acetabular anteversion and femoral anteversion values on 2D slice images were 42.01[Formula: see text], 18.64[Formula: see text] and 14.44[Formula: see text], respectively, while those using images of 3D reconstructed bone models were 52.80[Formula: see text], 14.98[Formula: see text] and 17.26[Formula: see text]. Intra-rater reliabilities for acetabular inclination, acetabular anteversion, and femoral anteversion on 2D slice images were 0.55, 0.81, and 0.85, respectively, while those for 3D measurements were 0.98, 0.99, and 0.98. Inter-rater reliabilities for acetabular inclination, acetabular anteversion and femoral anteversion on 2D slice images were 0.48, 0.86, and 0.84, respectively, while those for 3D measurements were 0.97, 0.99, and 0.97. The differences between the two measurements are explained by the use of different tools. However, more consistent measurements were possible using the images of 3D reconstructed bone models. Therefore, 3D measurement can be a good alternative to measurement using 2D slice images.

Increased Mortality in Elderly Patients with Sarcopenia and Acetabular Fractures.

PubMed

Deren, Matthew E; Babu, Jacob; Cohen, Eric M; Machan, Jason; Born, Christopher T; Hayda, Roman

2017-02-01

Sarcopenia is a condition of clinically relevant loss of muscle mass and function. Acetabular fractures in elderly patients are common and difficult to treat. This study aimed to determine if sarcopenia is common in elderly patients with acetabular fractures and correlates with lower-energy mechanisms of injury, higher rates of complications, and higher mortality than patients with normal muscle mass. The Rhode Island Hospital Trauma Database was queried for patients who were ≥60 years of age from 2005 to 2014 using the International Classification of Diseases, Ninth Revision, code for closed acetabular fracture, 808.0. Charts were retrospectively reviewed for demographic data, operative intervention, mechanism of injury, mortality, comorbidities, and other factors. Computed tomography (CT) was used to determine the muscle cross-sectional area and to calculate the skeletal muscle index. The database revealed 192 patients coded for acetabular fracture; of these, 181 were correctly diagnosed. Ninety-nine patients had recorded body mass index (BMI) and adequate CT scans to measure the skeletal muscle index. Forty-two patients (42.4%) had sarcopenia, and 57 patients (57.6%) did not have sarcopenia. There were no significant differences in demographic characteristics between the groups with the exception of BMI and sex. BMI was higher in patients who did not have sarcopenia (31.7 kg/m) than it was in patients with sarcopenia (23.6 kg/m) (p < 0.001). Male sex was significantly greater (p = 0.0104) in patients with sarcopenia at 76.2% (32 of 42 patients) than in patients without sarcopenia at 50.9% (29 of 57 patients). Fractures in patients without sarcopenia were associated with a higher-energy mechanism of injury in 78.9% of cases compared with 52.4% of cases of patients with sarcopenia (p = 0.005). Sarcopenia was significantly associated (p = 0.0419) with increased 1-year mortality (28.6%) compared with the absence of sarcopenia (12.3%). This association was even

Stabilization of an acetabular fracture with cables for acute total hip arthroplasty.

PubMed

Mears, D C; Shirahama, M

1998-01-01

A critical stage of total hip arthroplasty for an acute acetabular fracture where extensive comminution, impaction, and osteopenia thwart the application of conventional open or closed methods, especially in the elderly, is stable fixation of the acetabulum. The use of 2-mm braided cables permits effective immobilization of the fracture for use in conjunction with a hybrid arthroplasty. The method is consistent with the use of a conventional arthroplastic incision and is suitable for other applications including the fixation of periprosthetic fractures, bulk allografts, and conventional acetabular fractures.

Complications Are Not Increased With Acetabular Revision of Metal-on-metal Total Hip Arthroplasty.

PubMed

Penrose, Colin T; Seyler, Thorsten M; Wellman, Samuel S; Bolognesi, Michael P; Lachiewicz, Paul F

2016-10-01

Isolated revision of the acetabular component in the setting of total hip arthroplasty has an increased risk of dislocation. With local soft tissue destruction frequently associated with failed metal-on-metal (MoM) bearings, it is presumed that acetabular revision of these hips will have even greater risk of complications. However, no study directly compares the complications of MoM with metal-on-polyethylene (MoP) acetabular revisions. In the context of a large database analysis, we asked the following questions: (1) Are there differences in early medical or wound complications after isolated acetabular revision of MoM and MoP bearing surfaces? (2) Are there differences in the frequency of dislocation, deep infection, and rerevision based on the bearing surface of the original implant? A review of the 100% Medicare database from 2005 to 2012 was performed using International Classification of Diseases, 9th Revision and Current Procedural Terminology codes. We identified 451 patients with a MoM bearing and 628 patients with a MoP bearing who had an isolated acetabular revision and a minimum followup of 2 years. The incidence, odds ratios, and 95% confidence intervals for early medical or wound complications were calculated using a univariate analysis at 30 days with patient sex and age group-adjusted analysis for blood transfusion. The incidence, odds ratio, and 95% confidence intervals for dislocation, deep infection, and rerevision were calculated using a univariate analysis at 30 day, 90 days, 1 year, and 2 years using a subgroup analysis with the Cochran-Mantel-Haenszel test to adjust for patient gender and age groups. There were no differences between the MoM and MoP isolated acetabular revisions in the incidence of 30-day local complications. There was a greater risk of transfusion in the MoP group than the MoM group (134 of 451 [30%] versus 230 of 628 [37%]; odds ratio [OR], 0.731; 95% confidence interval [CI], 0.565-0.948; p = 0.018). There were no

21 CFR 888.3320 - Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Hip joint metal/metal semi-constrained, with a... Devices § 888.3320 Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis. (a) Identification. A hip joint metal/metal semi-constrained, with a cemented acetabular...

21 CFR 888.3320 - Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Hip joint metal/metal semi-constrained, with a... Devices § 888.3320 Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis. (a) Identification. A hip joint metal/metal semi-constrained, with a cemented acetabular...

Pelvic ring injuries: Surgical management and long-term outcomes

PubMed Central

Halawi, Mohamad J.

2016-01-01

Pelvic ring injuries present a therapeutic challenge to the orthopedic surgeon. Management is based on the patient's physiological status, fracture classification, and associated injuries. Surgical stabilization is indicated in unstable injury patterns and those that fail nonsurgical management. The optimal timing for definitive fixation is not clearly defined, but early stabilization is recommended. Surgical techniques include external fixation, open reduction and internal fixation, and minimally invasive percutaneous osteosynthesis. Special considerations are required for concomitant acetabular fractures, sacral fractures, and those occurring in skeletally immature patients. Long-term outcomes are limited by lack of pelvis-specific outcome measures and burden of associated injuries. PMID:26908968

Assessment of acetabular retroversion following long term review of Salter's osteotomy.

PubMed

Robb, Curtis A; Datta, Amit; Nayeemuddin, Mohammed; Bache, Christopher E

2009-01-01

Salter's innominate osteotomy may predispose to anterior over-coverage of the acetabulum. Over cover or retroversion has been demonstrated to be a cause of hip pain, impingement and subsequent osteoarthritis. We reviewed the long-term follow up of seventeen skeletally mature hips in sixteen patients who had previously undergone a Salter's osteotomy in childhood. The Salter pelvic osteotomy was performed at a mean average age of 5 years and follow up at a mean average age of 20 years. Patients were assessed by clinical examination for signs of impingement, Harris Hip Score and pelvic radiograph. Acetabular version was evaluated by the relationship between anterior and posterior walls of the acetabulum using templates applied to the pelvic radiograph as described by Hefti. The median acetabular cover averaged 17 degrees of anteversion with 2 patients (12%) demonstrating retroversion, neither of whom, had signs of impingement on examination. The mean average Harris Hip Score was 85 indicating a good outcome at long-term follow-up. We believe acetabular remodelling may occur with age after Salter's innominate osteotomy and have found good results in patients after skeletal maturation. Fears of long-term anterior over-coverage and retroversion with this operation may be unfounded.

Initial stability of press-fit acetabular components under rotational forces.

PubMed

Fehring, Keith A; Owen, John R; Kurdin, Anton A; Wayne, Jennifer S; Jiranek, William A

2014-05-01

The primary goal of this study was to determine the initial press-fit stability in acetabular components without screw fixation. Mechanical testing was performed with the implantation of press-fit acetabular components in cadaveric specimens. No significant difference was found in load to failure testing between 1 and 2 mm of under-reaming. However, there was significant variability in bending forces required to create 150 μm of micromotion ranging from 49.3 N to 214.4 N. This study shows that cups implanted in a press-fit fashion, which are felt to be clinically stable, have high degrees of variability in resisting load and may be at risk for loosening. There is a need for more objective intra-operative techniques to test cup stability. © 2014.

The influence of acetabular bone cracks in the press-fit hip replacement: Numerical and experimental analysis.

PubMed

Ramos, A; Duarte, R J; Relvas, C; Completo, A; Simões, J A

2013-07-01

The press-fit hip acetabular prosthesis implantation can cause crack formation in the thin regions surrounding the acetabular. As a consequence the presence of cracks in this region can lead to poor fixation and fibrous tissue formation. Numerical and experimental models of commercial press-fit hip replacements were developed to compare the behavior between the intact and implanted joints. Numerical models with an artificial crack and without crack were considered. The iliac and the femur were created through 3D geometry acquisition based on composite human replicas and 3D-Finite Element models were generated. The mechanical behavior was assessed numerically and experimentally considering the principal strains. The comparison between Finite Element model predictions and experimental measurements revealed a maximum difference of 9%. Similar distribution of the principal strains around the acetabular cavity was obtained for the intact and implanted models. When comparing the Von Mises stresses, it is possible to observe that the intact model is the one that presents the highest stress values in the entire acetabular cavity surface. The crack in the posterior side changes significantly the principal strain distribution, suggesting bone loss after hip replacement. Relatively to micromotions, these were higher on the superior side of the acetabular cavity and can change the implant stability and bone ingrowth. Copyright © 2013 Elsevier Ltd. All rights reserved.

[Pelvic reconstructions after bone tumor resection].

PubMed

Anract, Philippe; Biau, David; Babinet, Antoine; Tomeno, Bernard

2014-02-01

The three more frequent primitive malignant bone tumour which concerned the iliac bone are chondrosarcoma, following Ewing sarcoma and osteosarcoma. Wide resection remains the most important part of the treatment associated with chemotherapy for osteosarcoma and the Ewing sarcoma. Iliac wing resections and obdurate ring don't required reconstruction. However, acetabular resections and iliac wing resection with disruption of the pelvic ring required reconstruction to provide acceptable functional result. Acetabular reconstruction remains high technical demanding challenge. After isolated acetabular resection or associated to obdurate ring, our usual method of reconstruction is homolateral proximal femoral autograft and total hip prosthesis but it is possible to also used : saddle prosthesis, Mac Minn prosthesis with auto or allograft, modular prosthesis or custom made prosthesis, massive allograft with or without prosthesis and femoro-ilac arthrodesis. After resection of the iliac wing plus acetabulum, reconstruction can be performed by femoro-obturatrice and femora-sacral arthrodesis, homolateral proximal femoral autograft and prosthesis, femoral medialisation, massive allograft and massive allograft. Carcinological results are lesser than resection for distal limb tumor, local recurrence rate range 17 to 45%. Functional results after Iliac wing and obdurate ring are good. However, acetabular reconstruction provide uncertain functional results. The lesser results arrive after hemipelvic or acetabular and iliac wing resection-reconstruction, especially when gluteus muscles were also resected. The most favourable results arrive after isolated acetabular or acetabular plus obturateur ring resection-reconstruction.

A Pilot Study of Augmented Reality Technology Applied to the Acetabular Cup Placement During Total Hip Arthroplasty.

PubMed

Ogawa, Hiroyuki; Hasegawa, Seiichirou; Tsukada, Sachiyuki; Matsubara, Masaaki

2018-06-01

We developed an acetabular cup placement device, the AR-HIP system, using augmented reality (AR). The AR-HIP system allows the surgeon to view an acetabular cup image superimposed in the surgical field through a smartphone. The smartphone also shows the placement angle of the acetabular cup. This preliminary study was performed to assess the accuracy of the AR-HIP system for acetabular cup placement during total hip arthroplasty (THA). We prospectively measured the placement angles using both a goniometer and AR-HIP system in 56 hips of 54 patients undergoing primary THA. We randomly determined the order of intraoperative measurement using the 2 devices. At 3 months after THA, the placement angle of the acetabular cup was measured on computed tomography images. The primary outcome was the absolute value of the difference between intraoperative and postoperative computed tomography measurements. The measurement angle using AR-HIP was significantly more accurate in terms of radiographic anteversion than that using a goniometer (2.7° vs 6.8°, respectively; mean difference 4.1°; 95% confidence interval, 3.0-5.2; P < .0001). There was no statistically significant difference in terms of radiographic inclination (2.1° vs 2.6°; mean difference 0.5°; 95% confidence interval, -1.1 to 0.1; P = .13). In this pilot study, the AR-HIP system provided more accurate information regarding acetabular cup placement angle than the conventional method. Further studies are required to confirm the utility of the AR-HIP system as a navigation tool. Copyright © 2018 Elsevier Inc. All rights reserved.

[A simulative biomechanical experiment on different position of none-cement acetabular components influencing the load distribution around acetabulum].

PubMed

Li, Dongsong; Liu, Jianguo; Li, Shuqiang; Fan, Honghui; Guan, Jikui

2008-02-01

In the present study, a three dimensional finite-element model of the human pelvic was reconstructed, and then, under different acetabular component position (the abduction angle ranges from 30 degrees to 70 degrees and the anteversion ranges from 5 degrees to 30degrees) the load distribution around the acetabular was evaluated by the computer biomechanical analysis program (Solidworks). Through the obtained load distribution results, the most even and reasonable range of the distribution was selected; therefore the safe range of the acetabular component implantation can be validated from the biomechanics aspect.

Can acetabular orientation be restored by lumbar pedicle subtraction osteotomy in ankylosing spondylitis patients with thoracolumbar kyphosis?

PubMed

Hu, Jun; Qian, Bang-Ping; Qiu, Yong; Wang, Bin; Yu, Yang; Zhu, Ze-Zhang; Jiang, Jun; Mao, Sai-Hu; Qu, Zhe; Zhang, Yun-Peng

2017-07-01

To evaluate whether acetabular orientation (abduction and anteversion) can be restored by lumbar pedicle subtraction osteotomy (PSO) in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis. A total of 33 consecutive AS patients with thoracolumbar kyphosis undergoing one-level lumbar PSO were retrospectively reviewed. Radiographical measurements included sagittal vertical axis, global kyphosis, thoracic kyphosis, local kyphosis, lumbar lordosis, pelvic incidence, sacral slope, and pelvic tilt. Acetabular abduction and anteversion were measured on CT scans of the pelvis before and after lumbar PSO. The preoperative and postoperative parameters were compared by the paired samples t test. Pearson's correlation analysis was conducted to determine the correlations between the changes in acetabular abduction and anteversion and the changes in sagittal spinopelvic parameters. After lumbar PSO, sagittal vertical axis, global kyphosis, and pelvic tilt were corrected from 15.7 ± 6.7 cm, 66.8° ± 17.5°, and 38.6° ± 9.0° to 2.9 ± 4.9 cm, 21.3° ± 8.2°, and 23.2° ± 8.2°, respectively (p < 0.001). Of note, acetabular abduction and anteversion decreased from 59.6° ± 4.6° to 31.4° ± 6.5° before surgery to 51.4° ± 6.5° and 20.2° ± 4.4° after surgery, respectively (p < 0.001). Moreover, the changes in acetabular abduction and anteversion were observed significantly correlated with the change in pelvic tilt (r = 0.527, p = 0.002; r = 0.586, p < 0.001). Abnormal acetabular abduction and anteversion could be corrected by lumbar PSO in AS patients with thoracolumbar kyphosis. Consequently, a relatively normal acetabular orientation could be achieved after lumbar PSO, which might decrease the potential risk of dislocation in AS patients with spine and hip deformities requiring subsequent THR surgery.

The Evolution of the Cup-Cage Technique for Major Acetabular Defects: Full and Half Cup-Cage Reconstruction.

PubMed

Sculco, Peter K; Ledford, Cameron K; Hanssen, Arlen D; Abdel, Matthew P; Lewallen, David G

2017-07-05

Complex acetabular reconstruction for major bone loss can require advanced methods such as the use of a cup-cage construct. The purpose of this study was to review outcomes after the initial development of the cup-cage technique and the subsequent evolution to the use of a half cup-cage construct. We performed a retrospective, single-center review of 57 patients treated with cup-cage reconstruction for major acetabular bone loss. All patients had major acetabular defects graded as Paprosky Type 2B through 3B, with 34 (60%) having an associated pelvic discontinuity. Thirty patients received a full cup-cage construct and 27, a half cup-cage construct. The mean follow-up was 5 years. Both the full and half cup-cage cohorts demonstrated significantly improved Harris hip score (HHS) values, from 36 to 72 at a minimum of 2 years of follow-up (p < 0.05). Early construct migration occurred in 4 patients, with stabilization prior to 2-year follow-up in all but 1 patient. Incomplete, zone-3, nonprogressive acetabular radiolucencies were observed in 2 (7%) of the full cup-cage constructs and 6 (22%) of the half cup-cage constructs. One patient with a full cup-cage construct underwent re-revision of the acetabular component for progressive migration and aseptic loosening. Short-term survivorship free from re-revision for any cause or reoperation was 89% (83% and 96% for full and half cup-cage cohorts, respectively). Both full and half cup-cage constructs demonstrated successful clinical outcomes and survivorship in the treatment of major acetabular defects and pelvic discontinuity. Each method is utilized on the basis of individual intraoperative findings, including the extent and pattern of bone loss, the quality and location of host bone remaining after preparation, and the presence of pelvic discontinuity. Longer-term follow-up is required to understand the durability of these constructs in treating major acetabular defects and pelvic discontinuity. Therapeutic Level III

Long-term results with the Atlas IIIp elastic cementless acetabular component in total hip replacement.

PubMed

Lee, Paul Yuh Feng; Rachala, Madhu; Teoh, Kar Ho; Woodnutt, David John

2016-09-01

Modular cementless elastic acetabular systems have advantages over cemented and hard shell cementless acetabular systems. There are few reports on the medium-term and long-term follow up of this particular type of implant. This study describes our experience with the Atlas IIIp modular acetabular system, which is a thin shell cementless elastic acetabular implant for total hip replacement commercialized under this name in many countries. We prospectively followed 244 patients treated with Atlas IIIp acetabular system between 2001 and 2004. Minimum ten year follow up was available for 148 hips (139 patients) from the original cohort of 263 hips (244 patients). One hundred five patients had died from unrelated causes and were excluded from the results. Post-operative and follow up radiographs of patients were assessed; and Harris hip scores were used as clinical outcome. Revision for any reason was defined as the end point for survivorship analysis. The mean pre-operative Harris hip score was 48 (S.D. 16) and the average post-operative score was 82 (S.D. 12). The mean follow up in our series was 11.5 years, ranging from ten to 13.5 years. Thirteen hips required further surgery in our cohort; of which ten cases required cup revision. The 13-years cumulative implant survival was 91.2 % and the risk of implant revision was 8.8 % at 13 years in 148 hips (139 patients). Kaplan-Meier analysis showed the implant survival rate of 95.2 % at ten years for revision for any reason and 99.4 % for aseptic loosening. Our clinical experience with this acetabular cup suggests good long-term survival rates that are similar to other cups on the market. The clinical experience in this study shows long-term survival rates that are consistent, acceptable and good results achieved with a low revision rate. Therapeutic III; therapeutic study.

Sex assessment from the acetabular rim by means of image analysis.

PubMed

Benazzi, S; Maestri, C; Parisini, S; Vecchi, F; Gruppioni, G

2008-08-25

Determining sex from skeletal remains is one of the most important steps in archaeological and forensic anthropology. The present study considers the diagnostic value of the acetabulum based on its planar image and related metric data. For this purpose, 83 adult os coxae of known age were examined. Digital photos of the acetabular area were taken, with each bone in a standardized orientation. Technical drawing software was used to trace the acetabular rim and to measure the related dimensions (area, perimeter, longitudinal and transverse maximum width). The measurements were subjected to SPSS discriminant and classification function analysis. There were significant differences (p

A novel approach for determining three-dimensional acetabular orientation: results from two hundred subjects.

PubMed

Higgins, Sean W; Spratley, E Meade; Boe, Richard A; Hayes, Curtis W; Jiranek, William A; Wayne, Jennifer S

2014-11-05

The inherently complex three-dimensional morphology of both the pelvis and acetabulum create difficulties in accurately determining acetabular orientation. Our objectives were to develop a reliable and accurate methodology for determining three-dimensional acetabular orientation and to utilize it to describe relevant characteristics of a large population of subjects without apparent hip pathology. High-resolution computed tomography studies of 200 patients previously receiving pelvic scans for indications not related to orthopaedic conditions were selected from our institution's database. Three-dimensional models of each osseous pelvis were generated to extract specific anatomical data sets. A novel computational method was developed to determine standard measures of three-dimensional acetabular orientation within an automatically identified anterior pelvic plane reference frame. Automatically selected points on the osseous ridge of the acetabulum were used to generate a best-fit plane for describing acetabular orientation. Our method showed excellent interobserver and intraobserver agreement (an intraclass correlation coefficient [ICC] of >0.999) and achieved high levels of accuracy. A significant difference between males and females in both anteversion (average, 3.5°; 95% confidence interval [CI], 1.9° to 5.1° across all angular definitions; p < 0.0001) and inclination (1.4°; 95% CI, 0.6° to 2.3° for anatomic angular definition; p < 0.002) was observed. Intrapatient asymmetry in anatomic measures showed bilateral differences in anteversion (maximum, 12.1°) and in inclination (maximum, 10.9°). Significant differences in acetabular orientation between the sexes can be detected only with accurate measurements that account for the entire acetabulum. While a wide range of interpatient acetabular orientations was observed, the majority of subjects had acetabula that were relatively symmetrical in both inclination and anteversion. A highly accurate and

Direct hip joint distraction during acetabular fracture surgery using the AO universal manipulator.

PubMed

Calafi, L Afshin; Routt, M L Chip

2010-02-01

Certain acetabular fractures may necessitate distraction of the hip joint for removal of intra-articular debris and assessment of reduction. Distraction can be accomplished by manual traction, using a traction table or an AO universal manipulator (UM). The UM is a relatively simple and an inexpensive device that can provide focal distraction in a controlled manner without the risks associated with the use of a traction table. We describe a technique using the UM for hip joint distraction during acetabular fracture surgery through a Kocher-Langenbeck surgical exposure.

[APPLICATION AND EFFECTIVENESS OF BIOLOGICAL TYPE ACETABULAR CUP IN ADULT Crowe TYPE IV DEVELOPMENTAL DYSPLASIA OF THE HIP].

PubMed

Xu, Ning; Sun, Junying; Zhao, Xijiang; Wang, Tao

2016-01-01

To investigate the application and effectiveness of the biological type acetabular cup(diameter < 44 mm) in adult Crowe type IV developmental dysplasia of the hip (DDH). Between April 2001 andAugust 2013, biological type acetabular cup was used in total hip arthroplasty for the treatment of Crowe type IV DDH in16 cases (20 hips). There were 3 males and 13 females, aged 31-69 years (mean, 49 years). Unilateral hip was involved in 12cases, and bilateral hips in 4 cases. The patients showed pain of the hip joint and inequality of lower limb (shortening ofaffected limb 1.8-6.0 cm in length, 3.5 cm on average). Acetabular deformity, the relationship and the severity of femoralhead dislocation were comfirmed on the X-ray films. The preoperative Harris score was 34.0 ± 6.9. All patientsachieved healing of incision by first intention, with no complication of infection or neurovascular injury. Sixteen caseswere followed up 4-12 years (mean, 7.5 years). At 2 weeks after operation, dislocation occurred in 2 cases, and were fixedwith plaster for 3 weeks after reduction of the hip. Postoperative X-ray films showed complete reduction of femoral head;the average acetabular coverage of the cup of the weight-bearing area was 98.5% (range, 98.2%-99.1%). The cup from theRanawat triangle was 4.6-7.0 mm (mean, 5.8 mm) in medial shifting, and was 4.5-7.9 mm (mean, 6.2 mm) in elevation,it located at cup lateral surface area inside the iliopectineal line and the Kohler line (< 40%); the cup abduction angle was(45 ± 5)degrees, and the anteversion angle was (10 ± 5)degrees. The other patients had no prosthesis loosening except 1 patient havingextensive acetabular prosthesis loosening because of acetabular osteolysis at 12 years after operation. The hip Harris scorewas significantly improved to 85.0 ± 7.5 at 1 year after operation (t = 14.34, P = 0.01). The acetabular grindingprocess to retain enough bone combined with a small cup of-biological prosthesis treating adult Crowe type IV DDH

Well-fixed acetabular component retention or replacement: the whys and the wherefores.

PubMed

Blaha, J David

2002-06-01

Occasionally the adult reconstructive surgeon is faced with a well-fixed acetabular component that is associated with an arthroplasty problem that ordinarily would require removal and replacement of the cup. Removal of a well-fixed cup is associated with considerable morbidity in bone loss, particularly in the medial wall of the acetabulum. In such a situation, retention of the cup with exchange only of the polyethylene liner may be possible. As preparation for a prospective study, I informally reviewed my experience of cup retention or replacement in revision total hip arthroplasty. An algorithm for retaining or revising a well-fixed acetabular component is presented here. Copyright 2002, Elsevier Science (USA).

Early failure mechanisms of constrained tripolar acetabular sockets used in revision total hip arthroplasty.

PubMed

Cooke, Christopher C; Hozack, William; Lavernia, Carlos; Sharkey, Peter; Shastri, Shani; Rothman, Richard H

2003-10-01

Fifty-eight patients received an Osteonics constrained acetabular implant for recurrent instability (46), girdlestone reimplant (8), correction of leg lengthening (3), and periprosthetic fracture (1). The constrained liner was inserted into a cementless shell (49), cemented into a pre-existing cementless shell (6), cemented into a cage (2), and cemented directly into the acetabular bone (1). Eight patients (13.8%) required reoperation for failure of the constrained implant. Type I failure (bone-prosthesis interface) occurred in 3 cases. Two cementless shells became loose, and in 1 patient, the constrained liner was cemented into an acetabular cage, which then failed by pivoting laterally about the superior fixation screws. Type II failure (liner locking mechanism) occurred in 2 cases. Type III failure (femoral head locking mechanism) occurred in 3 patients. Seven of the 8 failures occurred in patients with recurrent instability. Constrained liners are an effective method for treatment during revision total hip arthroplasty but should be used in select cases only.

A new method for the measurement of anteversion of the acetabular cup after total hip arthroplasty.

PubMed

Aydogan, Mehmet; Burç, Halil; Saka, Gursel

2014-08-01

Many methods of determining the anteversion of the acetabular cup have been described in the literature. The advantages and disadvantages of each of these methods are discussed in this paper. We present a new method of measuring the acetabular anteversion at the anteroposterior hip. The formula designed by the authors was anteversion angle (α) = arc sin |PK|/√ |AK| × |BK|. The formula was tested using the AutoCAD software, and an experimental study was conducted to evaluate the accuracy. Three groups were created, and 16 X-ray images were taken and coded. Ten orthopaedic surgeons measured the acetabular anteversion from these X-rays using our formula. The results in Group 1 were closer to the actual value; in contrast, the results in Group 2 differed from the actual values. The results in Group 3 were as close to the actual anteversion values as were those in Group 1. Developments in technology often bring an increase in complications. Despite newly developed surgical methods and technology, the position of the acetabular cup is still used to determine the results of a total hip arthroplasty. Our method is simple, cost-effective and achieves almost 100 % accuracy.

Computer-assisted virtual preoperative planning in orthopedic surgery for acetabular fractures based on actual computed tomography data.

PubMed

Wang, Guang-Ye; Huang, Wen-Jun; Song, Qi; Qin, Yun-Tian; Liang, Jin-Feng

2016-12-01

Acetabular fractures have always been very challenging for orthopedic surgeons; therefore, appropriate preoperative evaluation and planning are particularly important. This study aimed to explore the application methods and clinical value of preoperative computer simulation (PCS) in treating pelvic and acetabular fractures. Spiral computed tomography (CT) was performed on 13 patients with pelvic and acetabular fractures, and Digital Imaging and Communications in Medicine (DICOM) data were then input into Mimics software to reconstruct three-dimensional (3D) models of actual pelvic and acetabular fractures for preoperative simulative reduction and fixation, and to simulate each surgical procedure. The times needed for virtual surgical modeling and reduction and fixation were also recorded. The average fracture-modeling time was 45 min (30-70 min), and the average time for bone reduction and fixation was 28 min (16-45 min). Among the surgical approaches planned for these 13 patients, 12 were finally adopted; 12 cases used the simulated surgical fixation, and only 1 case used a partial planned fixation method. PCS can provide accurate surgical plans and data support for actual surgeries.

Acetabular Global Insufficiency in Patients with Down Syndrome and Hip-Related Symptoms: A Matched-Cohort Study.

PubMed

Bulat, Evgeny; Maranho, Daniel A; Kalish, Leslie A; Millis, Michael B; Kim, Young-Jo; Novais, Eduardo N

2017-10-18

The etiology of hip instability in Down syndrome is not completely understood. We investigated the morphology of the acetabulum and femur in patients with Down syndrome and compared measurements of the hips with those of matched controls. Computed tomography (CT) images of the pelvis of 42 patients with Down syndrome and hip symptoms were compared with those of 42 age and sex-matched subjects without Down syndrome or history of hip disease who had undergone CT for abdominal pain. Each of the cohorts had 23 male and 19 female subjects. The mean age (and standard deviation) in each cohort was 11.3 ± 5.3 years. The lateral center-edge angle (LCEA), acetabular inclination angle (IA), acetabular depth-width ratio (ADR), acetabular version, and anterior and posterior acetabular sector angles (AASA and PASA) were compared. The neck-shaft angle and femoral version were measured in the patients with Down syndrome only. The hips of the patients with Down syndrome were further categorized as stable (n = 21) or unstable (n = 63) for secondary analysis. The hips in the Down syndrome group had a smaller LCEA (mean, 10.8° ± 12.6° compared with 25.6° ± 4.6°; p < 0.0001), a larger IA (mean, 17.4° ± 10.3° compared with 10.9° ± 4.8°; p < 0.0001), a lower ADR (mean, 231.9 ± 56.2 compared with 306.8 ± 31.0; p < 0.0001), a more retroverted acetabulum (mean acetabular version as measured at the level of the centers of the femoral heads [AVC], 7.8° ± 5.1° compared with 14.0° ± 4.5°; p < 0.0001), a smaller AASA (mean, 55.0° ± 9.9° compared with 59.7° ± 7.8°; p = 0.005), and a smaller PASA (mean, 67.1° ± 10.4° compared with 85.2° ± 6.8°; p < 0.0001). Within the Down syndrome cohort, the unstable hips showed greater femoral anteversion (mean, 32.7° ± 14.6° compared with 23.6° ± 10.6°; p = 0.002) and worse global acetabular insufficiency compared with the stable hips. No differences between the unstable and stable hips were found with respect to

Morphometric analysis of acetabular dysplasia in cerebral palsy: three-dimensional CT study.

PubMed

Gose, Shinichi; Sakai, Takashi; Shibata, Toru; Murase, Tsuyoshi; Yoshikawa, Hideki; Sugamoto, Kazuomi

2009-12-01

Three-dimensional computed tomography (3D-CT) eliminates the positioning errors and allows the clinician to more accurately assess the radiographic parameters present. To elucidate the 3D geometry of the acetabulum and the extent of hip subluxation/dislocation in patients with cerebral palsy (CP), quantitative morphometric analysis was performed using 3D-CT data. We evaluated 150 hips in 75 patients with bilateral spastic CP. The mean age of the patients was 5.4 years (range: 2.7 to 6.9 y). The fitting plane of the ilium was projected onto the coronal plane and then onto the sagittal plane, and then the angle formed with a horizontal line was defined as CTalpha (the lateral opening angle) and CTbeta (the sagittal inclination angle), respectively. The center of the acetabulum and the femoral head were defined, and the distance between these centers was divided by the femoral head diameter, defined as CT migration percentage (CTMP, %). In 123 (82%) of the 150 hips, the femoral head center was located posteriorly, superiorly, and laterally relative to the acetabular center. Large CTalpha cases tended to show large CTMP. CTalpha and CTMP were significantly larger in the cases with Gross Motor Functional Classification System (GMFCS) level IV/V and spastic quadriplegia, than in the cases with GMFCS level II/III and spastic diplegia. CTbeta showed significant correlation with the acetabular defect on the lateral 3D reconstructed images. Three-dimensional acetabular geometry and migration percentage in CP patients can be analyzed quantitatively using 3D-CT regardless of the abnormal spastic posture. The extent of acetabular dysplasia and subluxation is more severe in patients with GMFCS level IV/V and spastic quadriplesia. Level 4.

The Bimetric cementless total hip replacement: 7-18 year follow-up assessing the influence of acetabular design on survivorship.

PubMed

Russell, R C; Ghassemi, A; Dorrell, J H; Powles, D P

2009-08-01

The purpose of this study was to evaluate the mid- to long-term survivorship of Bimetric cementless total hip replacement and assess how it is affected by the acetabular design. This was a retrospective analysis of 127 Bimetric cementless total hip replacements in 110 patients with a follow-up of 7-18 years. A single design stem and three different cementless metal-backed acetabular designs were used. Patients were assessed clinically using the Harris hip score and radiologically by independent review of current hip radiographs. There was only one case of aseptic loosening of the femoral stem. The earliest acetabular design showed a high failure rate whilst the latter two designs showed a 96% survivorship at a mean of 9.5 years. We conclude that a combination of the bimetric stem with either of the latter acetabular cup designs has a good mid- to long-term performance.

Accuracy of templating the acetabular cup size in Total Hip Replacement using conventional acetate templates on digital radiographs.

PubMed

Krishnamoorthy, Vignesh P; Perumal, Rajamani; Daniel, Alfred J; Poonnoose, Pradeep M

2015-12-01

Templating of the acetabular cup size in Total Hip Replacement (THR) is normally done using conventional radiographs. As these are being replaced by digital radiographs, it has become essential to create a technique of templating using digital films. We describe a technique that involves templating the digital films using the universally available acetate templates for THR without the use of special software. Preoperative digital radiographs of the pelvis were taken with a 30 mm diameter spherical metal ball strapped over the greater trochanter. Using standard acetate templates provided by the implant company on magnified digital radiographs, the size of the metal ball (X mm) and acetabular cup (Y mm) were determined. The size of the acetabular cup to be implanted was estimated using the formula 30*Y/X. The estimated size was compared with the actual size of the cup used at surgery. Using this technique, it was possible to accurately predict the acetabular cup size in 28/40 (70%) of the hips. When the accuracy to within one size was considered, templating was correct in 90% (36/40). When assessed by two independent observers, there was good intra-observer and inter-observer reliability with intra-class correlation coefficient values greater than 0.8. It was possible to accurately and reliably predict the size of the acetabular cup, using acetate templates on digital films, without any digital templates.

Visual reinforcement in the female Siamese fighting fish, Betta splendens.

PubMed

Elcoro, Mirari; Silva, Stephanie P; Lattal, Kennon A

2008-07-01

Operant conditioning with Betta splendens (Bettas) has been investigated extensively using males of the species. Ethological studies of female Bettas have revealed aggressive interactions that qualitatively parallel those between male Bettas. Given these similarities, four experiments were conducted with female Bettas to examine the generality of a widely reported finding with males: mirror-image reinforcement. Swimming through a ring was reinforced by a 10-s mirror presentation. As with males, ring swimming was acquired and maintained when mirror presentations were immediate (Experiments 1, 2, and 3) and delayed (Experiment 4). The failure of conventional extinction (Experiments 1 and 2) and response-independent mirror presentations (Experiment 3) to maintain responding confirmed the reinforcing properties of mirror presentation. These results extend previous findings of mirror images as reinforcers in males of the same species and illustrate a complementarity between behavioral ecology and the experimental analysis of behavior.

Validation of a 3D CT method for measurement of linear wear of acetabular cups.

PubMed

Jedenmalm, Anneli; Nilsson, Fritjof; Noz, Marilyn E; Green, Douglas D; Gedde, Ulf W; Clarke, Ian C; Stark, Andreas; Maguire, Gerald Q; Zeleznik, Michael P; Olivecrona, Henrik

2011-02-01

We evaluated the accuracy and repeatability of a 3D method for polyethylene acetabular cup wear measurements using computed tomography (CT). We propose that the method be used for clinical in vivo assessment of wear in acetabular cups. Ultra-high molecular weight polyethylene cups with a titanium mesh molded on the outside were subjected to wear using a hip simulator. Before and after wear, they were (1) imaged with a CT scanner using a phantom model device, (2) measured using a coordinate measurement machine (CMM), and (3) weighed. CMM was used as the reference method for measurement of femoral head penetration into the cup and for comparison with CT, and gravimetric measurements were used as a reference for both CT and CMM. Femoral head penetration and wear vector angle were studied. The head diameters were also measured with both CMM and CT. The repeatability of the method proposed was evaluated with two repeated measurements using different positions of the phantom in the CT scanner. The accuracy of the 3D CT method for evaluation of linear wear was 0.51 mm and the repeatability was 0.39 mm. Repeatability for wear vector angle was 17°. This study of metal-meshed hip-simulated acetabular cups shows that CT has the capacity for reliable measurement of linear wear of acetabular cups at a clinically relevant level of accuracy.

Early Versus Late Weight-Bearing Protocols for Surgically Managed Posterior Wall Acetabular Fractures.

PubMed

Heare, Austin; Kramer, Nicholas; Salib, Christopher; Mauffrey, Cyril

2017-07-01

Despite overall improved outcomes with open reduction and internal fixation of acetabular fractures, posterior wall fractures show disproportionately poor results. The effect of weight bearing on outcomes of fracture management has been investigated in many lower extremity fractures, but evidence-based recommendations in posterior wall acetabular fractures are lacking. The authors systematically reviewed the current literature to determine if a difference in outcome exists between early and late postoperative weight-bearing protocols for surgically managed posterior wall acetabular fractures. PubMed and MEDLINE were searched for posterior wall acetabular fracture studies that included weight-bearing protocols and Merle d'Aubigné functional scores. Twelve studies were identified. Each study was classified as either early or late weight bearing. Early weight bearing was defined as full, unrestricted weight bearing at or before 12 weeks postoperatively. Late weight bearing was defined as restricted weight bearing for greater than 12 weeks postoperatively. The 2 categories were then compared by functional score using a 2-tailed t test and by complication rate using chi-square analysis. Six studies (152 fractures) were placed in the early weight-bearing category. Six studies (302 fractures) were placed in the late weight-bearing category. No significant difference in Merle d'Aubigné functional scores was found between the 2 groups. No difference was found regarding heterotopic ossification, avascular necrosis, superficial infections, total infections, or osteoarthritis. This systematic review found no difference in functional outcome scores or complication rates between early and late weight-bearing protocols for surgically treated posterior wall fractures. [Orthopedics. 2017: 40(4):e652-e657.]. Copyright 2017, SLACK Incorporated.

Postural correction reduces hip pain in adult with acetabular dysplasia: A case report.

PubMed

Lewis, Cara L; Khuu, Anne; Marinko, Lee N

2015-06-01

Developmental dysplasia of the hip is often diagnosed in infancy, but less severe cases of acetabular dysplasia are being detected in young active adults. The purpose of this case report is to present a non-surgical intervention for a 31-year-old female with mild acetabular dysplasia and an anterior acetabular labral tear. The patient presented with right anterior hip and groin pain, and she stood with the trunk swayed posterior to the pelvis (swayback posture). The hip pain was reproduced with the anterior impingement test. During gait, the patient maintained the swayback posture and reported 6/10 hip pain. Following correction of the patient's posture, the patient's pain rating was reduced to a 2/10 while walking. The patient was instructed to maintain the improved posture. At the 1 year follow-up, she demonstrated significantly improved posture in standing and walking. She had returned to recreational running and was generally pain-free. The patient demonstrated improvement on self-reported questionnaires for pain, function, and activity. These findings suggest that alteration of posture can have an immediate and lasting effect on hip pain in persons with structural abnormality and labral pathology. Copyright © 2015 Elsevier Ltd. All rights reserved.

Postural correction reduces hip pain in adult with acetabular dysplasia: a case report

PubMed Central

Lewis, Cara L.; Khuu, Anne; Marinko, Lee

2015-01-01

Developmental dysplasia of the hip is often diagnosed in infancy, but less severe cases of acetabular dysplasia are being detected in young active adults. The purpose of this case report is to present a non-surgical intervention for a 31-year-old female with mild acetabular dysplasia and an anterior acetabular labral tear. The patient presented with right anterior hip and groin pain, and she stood with the trunk swayed posterior to the pelvis (swayback posture). The hip pain was reproduced with the anterior impingement test. During gait, the patient maintained the swayback posture and reported 6/10 hip pain. Following correction of the patient’s posture, the patient’s pain rating was reduced to a 2/10 while walking. The patient was instructed to maintain the improved posture. At the 1 year follow-up, she demonstrated significantly improved posture in standing and walking. She had returned to recreational running and was generally pain-free. The patient demonstrated improvement on self-reported questionnaires for pain, function and activity. These findings suggest that alteration of posture can have an immediate and lasting effect on hip pain in persons with structural abnormality and labral pathology. PMID:25731688

Robotic-arm assisted total hip arthroplasty results in smaller acetabular cup size in relation to the femoral head size: a matched-pair controlled study.

PubMed

Suarez-Ahedo, Carlos; Gui, Chengcheng; Martin, Timothy J; Chandrasekaran, Sivashankar; Lodhia, Parth; Domb, Benjamin G

2017-03-31

To compare the acetabular component size relative to the patient's native femoral head size between conventional THA (CTHA) approach and robotic-arm assisted THA (RTHA) to infer which of these techniques preserved more acetabular bone. Patients were included if they had primary osteoarthritis (OA) and underwent total hip replacement between June 2008 and March 2014. Patients were excluded if they had missing or rotated postoperative anteroposterior radiographs. RTHA patients were matched to a control group of CTHA patients, in terms of preoperative native femoral head size, age, gender, body mass index (BMI) and approach. Acetabular cup size relative to femoral head size was used as a surrogate for amount of bone resected. We compared the groups according to 2 measures describing acetabular cup diameter (c) in relation to femoral head diameter (f): (i) c-f, the difference between cup diameter and femoral head diameter and (ii) (c-f)/f, the same difference as a fraction of femoral head diameter. 57 matched pairs were included in each group. There were no significant differences between groups for demographic measures, femoral head diameter, or acetabular cup diameter (p>0.05). However, measures (i) and (ii) did differ significantly between the groups, with lower values in the RTHA group (p<0.02). Using acetabular cup size relative to femoral head size as an approximate surrogate measure of acetabular bone resection may suggest greater preservation of bone stock using RTHA compared to CTHA. Further studies are needed to validate the relationship between acetabular cup size and bone loss in THA.

Validation of a 3D CT method for measurement of linear wear of acetabular cups

PubMed Central

2011-01-01

Background We evaluated the accuracy and repeatability of a 3D method for polyethylene acetabular cup wear measurements using computed tomography (CT). We propose that the method be used for clinical in vivo assessment of wear in acetabular cups. Material and methods Ultra-high molecular weight polyethylene cups with a titanium mesh molded on the outside were subjected to wear using a hip simulator. Before and after wear, they were (1) imaged with a CT scanner using a phantom model device, (2) measured using a coordinate measurement machine (CMM), and (3) weighed. CMM was used as the reference method for measurement of femoral head penetration into the cup and for comparison with CT, and gravimetric measurements were used as a reference for both CT and CMM. Femoral head penetration and wear vector angle were studied. The head diameters were also measured with both CMM and CT. The repeatability of the method proposed was evaluated with two repeated measurements using different positions of the phantom in the CT scanner. Results The accuracy of the 3D CT method for evaluation of linear wear was 0.51 mm and the repeatability was 0.39 mm. Repeatability for wear vector angle was 17°. Interpretation This study of metal-meshed hip-simulated acetabular cups shows that CT has the capacity for reliable measurement of linear wear of acetabular cups at a clinically relevant level of accuracy. PMID:21281259

Effect of end-ring stiffness on buckling of pressure-loaded stiffened conical shells

NASA Technical Reports Server (NTRS)

Davis, R. C.; Williams, J. G.

1977-01-01

Buckling studies were conducted on truncated 120 deg conical shells having large end rings and many interior reinforcing rings that are typical of aeroshells used as spacecraft decelerators. Changes in base-end-ring stiffness were accomplished by simply machining away a portion of the base ring between successive buckling tests. Initial imperfection measurements from the test cones were included in the analytical model.

[Aseptic, simultaneous and bilateral mobilisation due to an acetabular shell fracture in a 43 year-old patient].

PubMed

Ceretti, M; Fanelli, M; Pappalardo, S

2014-01-01

The acetabular shell mobilization is the main long-term complication in total hip replacement. Metal-back fracture has also to be considered among the possible causes of shell mobilization. A case is presented of bilateral acetabular shell mobilization due to the trabecular covering de-soldering from the metal-back in a 43 year-old patient, 13-14 years after the first surgery. Copyright © 2013 SECOT. Published by Elsevier Espana. All rights reserved.

Inversion of the acetabular labrum triggers rapidly destructive osteoarthritis of the hip: representative case report and proposed etiology.

PubMed

Fukui, Kiyokazu; Kaneuji, Ayumi; Fukushima, Mana; Matsumoto, Tadami

2014-12-01

The pathophysiology of rapidly destructive osteoarthritis (OA) of the hip is unknown. This study documented cases of inversion of the acetabular labrum, which has clinicoradiologic features similar to those of initial-stage rapidly destructive hip OA. Our study was based on a prospective review of data for 9 patients with rapidly destructive hip OA. Intraoperative findings showed that the anterosuperior portion of the acetabular labrum had inverted into the articular space, along with many fragments of articular cartilage, in all patients. Subchondral insufficiency fractures of the femoral heads were seen just under the inverted labra in 8 of the 9 patients. Inversion of the acetabular labrum may be involved in rapid joint-space narrowing and subchondral insufficiency fracture in rapidly destructive hip OA. Copyright © 2014 Elsevier Inc. All rights reserved.

A cemented cup with acetabular impaction bone grafting is more cost-effective than an uncemented cup in patients under 50 years.

PubMed

Busch, Vincent J J F; Verschueren, Joost; Adang, Eddy M; Lie, Stein A; Havelin, Leif I; Schreurs, Berend W

2016-01-01

Acetabular deficiencies in young patients can be restored in several ways during total hip arthroplasty. Currently, cementless cups are most frequently used. Impaction bone grafting of acetabular defects is a more biological approach, but is it cost-effective in young patients on the long term? We designed a decision model for a cost-utility analysis of a cemented cup with acetabular impaction bone grafting versus an uncemented cup, in terms of cost per quality-adjusted life year (QALY) for the young adult with acetabular bone deficiency, in need for a primary total hip arthroplasty. Outcome probabilities and effectiveness were derived from the Radboud University Nijmegen Medical Centre and the Norwegian Hip Register. Multiple sensitivity analyses were used to assess the contribution of the included variables in the model's outcome. Cemented cups with impaction bone grafting were more cost-effective compared to the uncemented option in terms of costs per QALY. A scenario suggesting equal primary survival rates of both cemented and uncemented cups still showed an effect gain of the cemented cup with impaction bone grafting, but at higher costs. Based on this model, the first choice of treatment of the acetabular bone deficient osteoarthritic hip in a young patient is reconstruction with impaction bone grafting and a cemented cup.

Examination of acetabular labral tear: a continued diagnostic challenge.

PubMed

Reiman, Michael P; Mather, Richard C; Hash, Thomas W; Cook, Chad E

2014-02-01

Acetabular labrum tears (ALT) are present in 22-55% of individuals with hip or groin pain. Tears can occur as a result of trauma or degeneration and are markedly associated with femoral acetabular morphological variations. An ALT can lead to biomechanical deficiencies and a loss of stability to the coxafemoral joint due to the labrum serving as a stabilising structure of this joint. The diagnosis of ALT is complex and multidimensional. Although tremendous improvements in diagnostic utility for ALT have occurred in the past 25 years, there are few patient history, clinical examination and special test findings that are unique to the condition. Imaging methods such as MRI, CT and ultrasonography have demonstrated reasonable accuracy, but not at a level that allows use as a stand-alone measure. Outcomes measures that focus on functional limitation or that are used to measure recovery should envelop the complexities of the condition and be captured using both self-report and physical performance measures. Only when patient history, objective testing, clinical examination special testing and imaging are combined can a clinician fully elucidate the multidimensional diagnosis of ALT.

Bilateral non-traumatic acetabular and femoral neck fractures due to pregnancy-associated osteoporosis.

PubMed

Aynaci, Osman; Kerimoglu, Servet; Ozturk, Cagatay; Saracoglu, Metehan

2008-03-01

Pregnancy-associated osteoporosis is a rare disorder and its pathophysiology remains unknown. We report a case of pregnancy-associated osteoporosis in a 27-year-old primiparous patient who revealed bilateral hip pain during early postnatal period. The plain radiographs and computerized tomography showed bilateral femoral neck and acetabular fractures. The diagnosis of osteoporosis was established by bone mineral density. Diagnostic work-up excluded a secondary osteoporosis. The case was treated successfully by bilateral cementless total hip arthroplasty. Bone mineral density increased after 2 years of treatment with calcium-vitamin D, calcitriol and alendronate. Diagnosis of pregnancy-associated osteoporosis should be suspected when hip pain occurs during pregnancy or in the post-partum period as it can lead to acetabular and femoral neck fractures.

The Bimetric cementless total hip replacement: 7–18 year follow-up assessing the influence of acetabular design on survivorship

PubMed Central

Ghassemi, A.; Dorrell, J. H.; Powles, D. P.

2008-01-01

The purpose of this study was to evaluate the mid- to long-term survivorship of Bimetric cementless total hip replacement and assess how it is affected by the acetabular design. This was a retrospective analysis of 127 Bimetric cementless total hip replacements in 110 patients with a follow-up of 7–18 years. A single design stem and three different cementless metal-backed acetabular designs were used. Patients were assessed clinically using the Harris hip score and radiologically by independent review of current hip radiographs. There was only one case of aseptic loosening of the femoral stem. The earliest acetabular design showed a high failure rate whilst the latter two designs showed a 96% survivorship at a mean of 9.5 years. We conclude that a combination of the bimetric stem with either of the latter acetabular cup designs has a good mid- to long-term performance. PMID:18551293

Interobserver reliability of the young-burgess and tile classification systems for fractures of the pelvic ring.

PubMed

Koo, Henry; Leveridge, Mike; Thompson, Charles; Zdero, Rad; Bhandari, Mohit; Kreder, Hans J; Stephen, David; McKee, Michael D; Schemitsch, Emil H

2008-07-01

The purpose of this study was to measure interobserver reliability of 2 classification systems of pelvic ring fractures and to determine whether computed tomography (CT) improves reliability. The reliability of several radiographic findings was also tested. Thirty patients taken from a database at a Level I trauma facility were reviewed. For each patient, 3 radiographs (AP pelvis, inlet, and outlet) and CT scans were available. Six different reviewers (pelvic and acetabular specialist, orthopaedic traumatologist, or orthopaedic trainee) classified the injury according to Young-Burgess and Tile classification systems after reviewing plain radiographs and then after CT scans. The Kappa coefficient was used to determine interobserver reliability of these classification systems before and after CT scan. For plain radiographs, overall Kappa values for the Young-Burgess and Tile classification systems were 0.72 and 0.30, respectively. For CT scan and plain radiographs, the overall Kappa values for the Young-Burgess and Tile classification systems were 0.63 and 0.33, respectively. The pelvis/acetabular surgeons demonstrated the highest level of agreement using both classification systems. For individual questions, the addition of CT did significantly improve reviewer interpretation of fracture stability. The pre-CT and post-CT Kappa values for fracture stability were 0.59 and 0.93, respectively. The CT scan can improve the reliability of assessment of pelvic stability because of its ability to identify anatomical features of injury. The Young-Burgess system may be optimal for the learning surgeon. The Tile classification system is more beneficial for specialists in pelvic and acetabular surgery.

The use of an Ossis custom 3D-printed tri-flanged acetabular implant for major bone loss: minimum 2-year follow-up: Short title: Ossis custom 3D-Printed tri-flanged acetabular implant.

PubMed

Kieser, David C; Ailabouni, Ramez; Kieser, Sandra C J; Wyatt, Michael C; Armour, Paul C; Coates, Mark H; Hooper, Gary J

2018-05-01

Custom 3D-printed acetabular implants are a new technology used in hip surgery with ever-increasing frequency. They offer patient-specific implants to optimise filling of bone defects and implant-bone contact, without the need for excessive bone resection. This is a retrospective cohort study of 46 consecutive patients who underwent an Ossis unilateral custom 3D-printed acetabular implant. Clinical (Oxford Hip Score OHS-60), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Harris Hip Score (HHS) and radiological (restoration of biomechanical hip centre, osteointegration, wear, heterotrophic ossification) results were assessed. Patient mean age was 68 years and follow-up was 38 months (minimum 24 months). 10 patients were excluded from the outcome analysis; 2 patients died, 1 required revision for deep infection and 7 were lost to follow-up. Of the 36 patients included, 21 had severe osteolysis. 7 were revised for infection, 3 for tumoural defects, 3 for metallosis, 1 for dysplasia and 1 for trauma (Paprosky 2a [n=6], 2b [n=2], 2c [n=5], 3a [n=6], 3b [n=11], pelvic dissociation [n=6]). OHS significantly improved postoperatively (16-8-48.4 p=0.027). Postoperative functional scores were good (WOMAC 98; HHS 79). The biomechanical hip centre was restored in all patients. 1 patient had early implant migration with subsequent stabilisation. 2 patients had radiographs concerning for failure of osteointegration. 1 patient had recurrent dislocations. The mid-term results of the Ossis custom 3D-printed tri-flanged acetabular implant for the management of severe acetabular defects are encouraging. The improvement in functional scores and radiographic outcomes are comparable to similar designs. In addition, no cases have required revision for aseptic loosening.

A combination of three-dimensional printing and computer-assisted virtual surgical procedure for preoperative planning of acetabular fracture reduction.

PubMed

Zeng, Canjun; Xing, Weirong; Wu, Zhanglin; Huang, Huajun; Huang, Wenhua

2016-10-01

Treatment of acetabular fractures remains one of the most challenging tasks that orthopaedic surgeons face. An accurate assessment of the injuries and preoperative planning are essential for an excellent reduction. The purpose of this study was to evaluate the feasibility, accuracy and effectiveness of performing 3D printing technology and computer-assisted virtual surgical procedures for preoperative planning in acetabular fractures. We hypothesised that more accurate preoperative planning using 3D printing models will reduce the operation time and significantly improve the outcome of acetabular fracture repair. Ten patients with acetabular fractures were recruited prospectively and examined by CT scanning. A 3-D model of each acetabular fracture was reconstructed with MIMICS14.0 software from the DICOM file of the CT data. Bone fragments were moved and rotated to simulate fracture reduction and restore the pelvic integrity with virtual fixation. The computer-assisted 3D image of the reduced acetabula was printed for surgery simulation and plate pre-bending. The postoperative CT scan was performed to compare the consistency of the preoperative planning with the surgical implants by 3D-superimposition in MIMICS14.0, and evaluated by Matta's method. Computer-based pre-operations were precisely mimicked and consistent with the actual operations in all cases. The pre-bent fixation plates had an anatomical shape specifically fit to the individual pelvis without further bending or adjustment at the time of surgery and fracture reductions were significantly improved. Seven out of 10 patients had a displacement of fracture reduction of less than 1mm; 3 cases had a displacement of fracture reduction between 1 and 2mm. The 3D printing technology combined with virtual surgery for acetabular fractures is feasible, accurate, and effective leading to improved patient-specific preoperative planning and outcome of real surgery. The results provide useful technical tips in

Preservation of the Acetabular Cup During Revision Total Hip Arthroplasty Using a Novel Mini-navigation Tool: A Case Report.

PubMed

Vincent, John; Alshaygy, Ibrahim; Muir, Jeffrey M; Kuzyk, Paul

2018-01-01

While intraoperative navigation systems have been shown to improve outcomes in primary total hip arthroplasty (THA), their use in the context of revision has been largely overlooked. This case report presents the first documented use of an imageless navigation tool in the context of revision THA, and an unexpected benefit to the surgical procedure as a result. An 84-year-old female patient presented following five episodes of dislocation of the left hip and with pain in the left buttock, groin, and posterior aspect of her hip. Relevant surgical history included primary hip arthroplasty in 1999 and the first revision in 2014. Preoperative analysis revealed a constrained liner that had become disengaged and migrated inferiorly, lodging at the distal aspect of the femoral neck. Acetabular protrusion was also noted. The pre-operative plan included the replacement of the fragmented liner and likely of the acetabular cup due to hardware failure. Intraoperative assessment, however, revealed that the cup was in good condition and would be difficult to remove due to substantial bony ingrowth. With the assistance of imageless navigation, the orientation of the acetabular cup was determined and a new constrained liner was cemented into the preexisting acetabular component at an altered orientation, correcting anteversion by 7°. In revision hip arthroplasty cases, image-based navigation is limited by the presence of existing implants and corresponding metal artefact. This case demonstrates the successful use of an imageless navigation tool for revision surgery. Use of navigation led to the unexpected intraoperative discovery that the acetabular cup was in an acceptable state, and allowed the surgical team to correct the position of the cup using a constrained liner, thus preserving the cup. This significantly benefitted patient outcome, due to the risks associated with the removal of a firmly fixated acetabular cup. While more extensive research is required, this case

Acetabular revisions using porous tantalum components: A retrospective study with 5-10 years follow-up

PubMed Central

Evola, Francesco Roberto; Costarella, Luciano; Evola, Giuseppe; Barchitta, Martina; Agodi, Antonella; Sessa, Giuseppe

2017-01-01

AIM To evaluate the clinical and X-ray results of acetabular components and tantalum augments in prosthetic hip revisions. METHODS Fifty-eight hip prostheses with primary failure of the acetabular component were reviewed with tantalum implants. The clinical records and X-rays of these cases were retrospectively reviewed. Bone defect evaluations were based on preoperative CT scans and classified according to Paprosky criteria of Radiolucent lines and periprosthetic gaps; implant mobilization and osteolysis were evaluated by X-ray. An ad hoc database was created and statistical analyses were performed with SPSS software (IBM SPSS Statistics for Windows, version 23.0). Statistical analyses were carried out using the Student’s t test for independent and paired samples. A P value of < 0.05 was considered statistically significant and cumulative survival was calculated by the Kaplan-Meier method. RESULTS The mean follow-up was 87.6 ± 25.6 mo (range 3-120 mo). 25 cases (43.1%) were classified as minor defects, and 33 cases (56.9%) as major defects. The preoperative HHS rating improved significantly from a mean of 40.7 ± 6.1 (range: 29-53) before revision, to a mean of 85.8 ± 6.1 (range: 70-94) at the end of the follow-up (Student’s t test for paired samples: P < 0.001). Considering HHS only at the end of follow-up, no statistically significant difference was observed between patients with a major or minor defect (Student’s t test for independent samples: P > 0.05). Radiolucent lines were found in 4 implants (6.9%). Postoperative acetabular gaps were observed in 5 hips (8.6%). No signs of implant mobilization or areas of periprosthetic osteolysis were found in the x-rays at the final follow-up. Only 3 implants failed: 1 case of infection and 2 cases of instability. Defined as the end-point, cumulative survival at 10 years was 95% (for all reasons) and 100% for aseptic loosening of the acetabular component. CONCLUSION The medium-term use of prosthetic tantalum

Acetabular revisions using porous tantalum components: A retrospective study with 5-10 years follow-up.

PubMed

Evola, Francesco Roberto; Costarella, Luciano; Evola, Giuseppe; Barchitta, Martina; Agodi, Antonella; Sessa, Giuseppe

2017-07-18

To evaluate the clinical and X-ray results of acetabular components and tantalum augments in prosthetic hip revisions. Fifty-eight hip prostheses with primary failure of the acetabular component were reviewed with tantalum implants. The clinical records and X-rays of these cases were retrospectively reviewed. Bone defect evaluations were based on preoperative CT scans and classified according to Paprosky criteria of Radiolucent lines and periprosthetic gaps; implant mobilization and osteolysis were evaluated by X-ray. An ad hoc database was created and statistical analyses were performed with SPSS software (IBM SPSS Statistics for Windows, version 23.0). Statistical analyses were carried out using the Student's t test for independent and paired samples. A P value of < 0.05 was considered statistically significant and cumulative survival was calculated by the Kaplan-Meier method. The mean follow-up was 87.6 ± 25.6 mo (range 3-120 mo). 25 cases (43.1%) were classified as minor defects, and 33 cases (56.9%) as major defects. The preoperative HHS rating improved significantly from a mean of 40.7 ± 6.1 (range: 29-53) before revision, to a mean of 85.8 ± 6.1 (range: 70-94) at the end of the follow-up (Student's t test for paired samples: P < 0.001). Considering HHS only at the end of follow-up, no statistically significant difference was observed between patients with a major or minor defect (Student's t test for independent samples: P > 0.05). Radiolucent lines were found in 4 implants (6.9%). Postoperative acetabular gaps were observed in 5 hips (8.6%). No signs of implant mobilization or areas of periprosthetic osteolysis were found in the x-rays at the final follow-up. Only 3 implants failed: 1 case of infection and 2 cases of instability. Defined as the end-point, cumulative survival at 10 years was 95% (for all reasons) and 100% for aseptic loosening of the acetabular component. The medium-term use of prosthetic tantalum components in prosthetic hip revisions is

Reduced survival for uncemented compared to cemented total hip arthroplasty after operatively treated acetabular fractures.

PubMed

Clarke-Jenssen, John; Westberg, Marianne; Røise, Olav; Storeggen, Stein Arne Øvre; Bere, Tone; Silberg, Ingunn; Madsen, Jan Erik

2017-11-01

Post traumatic arthritis and avascular necrosis of the femoral head are common complications after operatively treated acetabular fractures. This may cause severe disabilities for the patient, necessitating a total hip arthroplasty. Even though an arthroplasty may provide good symptomatic relief, the long-term results are more uncertain and no consensus exists according to preferred prosthetic designs. With this cohort study, we aimed to investigate the medium to long term arthroplasty survival and clinical results of total hip arthroplasty after operatively treated acetabular fractures. We included 52 patients treated with a secondary total hip arthroplasty at a median of 2.4 (0.1-14.1) years after an operatively treated acetabular fracture. The median age was 54 (11-82) years. Cemented arthroplasty was used for 33 patients, 10 patients had an uncemented arthroplasty and 9 patients received a hybrid arthroplasty. Average follow up was 8.0 (SD 5.0) years. Ten-year revision free arthroplasty survival was 79%. Uncemented arthroplasties had a significantly worse 10-year survival of 57%. Arthroplasties performed at a centre without a pelvic fracture service also had a significantly worse 10-years survival of 51%. Cox regression showed similar results with an 8-fold increase in risk of revision for both uncemented arthroplasties and operations performed at a non-pelvic trauma centre. Total hip arthroplasty secondary to an operatively treated acetabular fracture provides good symptomatic relief. These patients are, however, complex cases and are probably best treated at specialist centres with both pelvic trauma surgeons and arthroplasty surgeons proficient in complex revisions present. Copyright © 2017 Elsevier Ltd. All rights reserved.

Primary stability of a cementless acetabular cup in a cohort of patient-specific finite element models.

PubMed

O'Rourke, Dermot; Al-Dirini, Rami Ma; Taylor, Mark

2018-03-01

The primary stability achieved during total hip arthroplasty determines the long-term success of cementless acetabular cups. Pre-clinical finite element testing of cups typically use a model of a single patient and assume the results can be extrapolated to the general population. This study explored the variability in predicted primary stability of a Pinnacle ® cementless acetabular cup in 103 patient-specific finite element models of the hemipelvis and examined the association between patient-related factors and the observed variability. Cups were inserted by displacement-control into the FE models and then a loading configuration simulating a complete level gait cycle was applied. The cohort showed a range of polar gap of 284-1112 μm and 95th percentile composite peak micromotion (CPM) of 18-624 μm. Regression analysis was not conclusive on the relationship between patient-related factors and primary stability. No relationship was found between polar gap and micromotion. However, when the patient-related factors were categorised into quartile groups, trends suggested higher polar gaps occurred in subjects with small and shallow acetabular geometries and cup motion during gait was affected most by low elastic modulus and high bodyweight. The variation in primary stability in the cohort for an acetabular cup with a proven clinical track record may provide benchmark data when evaluating new cup designs. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1012-1023, 2018. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Study of the three-dimensional orientation of the labrum: its relations with the osseous acetabular rim

PubMed Central

Bonneau, Noémie; Bouhallier, July; Baylac, Michel; Tardieu, Christine; Gagey, Olivier

2012-01-01

Understanding the three-dimensional orientation of the coxo-femoral joint remains a challenge as an accurate three-dimensional orientation ensure an efficient bipedal gait and posture. The quantification of the orientation of the acetabulum can be performed using the three-dimensional axis perpendicular to the plane that passes along the edge of the acetabular rim. However, the acetabular rim is not regular as an important indentation in the anterior rim was observed. An innovative cadaver study of the labrum was developed to shed light on the proper quantification of the three-dimensional orientation of the acetabulum. Dissections on 17 non-embalmed corpses were performed. Our results suggest that the acetabular rim is better represented by an anterior plane and a posterior plane rather than a single plane along the entire rim as it is currently assumed. The development of the socket from the Y-shaped cartilage was suggested to explain the different orientations in these anterior and posterior planes. The labrum forms a plane that takes an orientation in between the anterior and posterior parts of the acetabular rim, filling up inequalities of the bony rim. The vectors VL, VA2 and VP, representing the three-dimensional orientation of the labrum, the anterior rim and the posterior rim, are situated in a unique plane that appears biomechanically dependent. The three-dimensional orientation of the acetabulum is a fundamental parameter to understand the hip joint mechanism. Important applications for hip surgery and rehabilitation, as well as for physical anthropology, were discussed. PMID:22360458

Change in Acetabular Cup Orientation From Supine to Standing Position and Its Effect on Wear of Highly Crosslinked Polyethylene.

PubMed

Teeter, Matthew G; Goyal, Prateek; Yuan, Xunhua; Howard, James L; Lanting, Brent A

2018-01-01

The purpose of this study is to measure acetabular cup position and wear of the highly crosslinked polyethylene liner in the supine and standing position for patients at a minimum of 10 years after the operation. A total of 38 patients were recruited at a mean of 12.5 years after the operation. All patients received a single acetabular cup design with a highly crosslinked liner and a 28-mm cobalt-chromium femoral head. Patients underwent supine and standing radiostereometric examinations in which the X-ray sources and detectors were positioned to obtain an anterior-posterior and cross-table lateral radiograph. Acetabular cup position and the three-dimensional wear rate were measured from the radiographs, and outcome scores were recorded for each patient. Anteversion significantly increased (P < .0001) a mean of 12° from supine (15.1° ± 10.4°) to standing (27.2° ± 10.5°) position. Inclination also significantly increased (P = .001) a mean of 2° from supine (44.4° ± 6.8°) to standing (46.3° ± 7.7°) position. There was no difference (P = .093) in wear rate between supine (0.067 ± 0.070 mm/y) and standing (0.073 ± 0.074 mm/y) positions. There were no correlations between cup orientation and wear rate in either position. Highly crosslinked polyethylene is a forgiving bearing material. Although adherence to the traditional acetabular position target zone is recommended, ensuring hip stability and consideration of the patient's functional position are also important objectives to consider for the acetabular position. Copyright © 2017 Elsevier Inc. All rights reserved.

Biomechanical study of pelvic discontinuity in failed total hip arthroplasty. Lessons learnt from the treatment of pelvic fractures.

PubMed

Ribes-Iborra, Julio; Atienza, Carlos; Sevil-De la Torre, Jorge; Gómez Pérez, Amelia

2017-11-01

Pelvic discontinuity is a rare but serious problem in orthopedic surgery. Acetabular reconstruction in case of severe bone loss after failed total hip arthroplasty is technically difficult, especially in segmental loss type III (anterior or posterior) or pelvic discontinuity (type IV). Acetabular reinforcement devices are frequently used as load-sharing devices to allow allograft incorporation and in order to serve as support of acetabular implants. This study tries to show, by means of biomechanic work, the efficiency of reinforced plate in anterior column in a segmental pelvic loss, illustrated with a clinical case, which shows the socket stability of hip prosthesis. © 2017 Elsevier Ltd. All rights reserved.

[Osteosynthesis and cup revision in periprosthetic acetabulum fractures using a Kocher-Langenbeck approach].

PubMed

Schwabe, P; Märdian, S; Perka, C; Schaser, K-D

2016-04-01

Reconstruction/stable fixation of the acetabular columns to create an adequate periacetabular requirement for the implantation of a revision cup. Displaced/nondisplaced fractures with involvement of the posterior column. Resulting instability of the cup in an adequate bone stock situation. Periprosthetic acetabulum fractures with inadequate bone stock. Extended periacetabular defects with loss of anchorage options. Isolated periprosthetic fractures of the anterior column. Septic loosening. Dorsal approach. Dislocation of hip. Mechanical testing of inlaying acetabular cup. With unstable cup situation explantation of the cup, fracture fixation of acetabulum with dorsal double plate osteosynthesis along the posterior column. Cup revision. Hip joint reposition. Early mobilization; partial weight bearing for 12 weeks. Thrombosis prophylaxis. Clinical and radiological follow-ups. Periprosthetic acetabular fracture in 17 patients with 9 fractures after primary total hip replacement (THR), 8 after revision THR. Fractures: 12 due to trauma, 5 spontaneously; 7 anterior column fractures, 5 transverse fractures, 4 posterior column fractures, 1 two column fracture after hemiendoprosthesis. 5 type 1 fractures and 12 type 2 fractures. Operatively treated cases (10/17) received 3 reinforcement ring, 2 pedestal cup, 1 standard revision cup, cup-1 cage construct, 1 ventral plate osteosynthesis, 1 dorsal plate osteosynthesis, and 1 dorsal plate osteosynthesis plus cup revision (10-month Harris Hip Score 78 points). Radiological follow-up for 10 patients: consolidation of fractures without dislocation and a fixed acetabular cup. No revision surgeries during follow-up; 2 hip dislocations, 1 transient sciatic nerve palsy.

The relationship between operative and radiographic acetabular component orientation: which factors influence resultant cup orientation?

PubMed

Grammatopoulos, G; Pandit, H G; da Assunção, R; McLardy-Smith, P; De Smet, K A; Gill, H S; Murray, D W

2014-10-01

There is great variability in acetabular component orientation following hip replacement. The aims of this study were to compare the component orientation at impaction with the orientation measured on post-operative radiographs and identify factors that influence the difference between the two. A total of 67 hip replacements (52 total hip replacements and 15 hip resurfacings) were prospectively studied. Intra-operatively, the orientation of the acetabular component after impaction relative to the operating table was measured using a validated stereo-photogrammetry protocol. Post-operatively, the radiographic orientation was measured; the mean inclination/anteversion was 43° (sd 6°)/ 19° (sd 7°). A simulated radiographic orientation was calculated based on how the orientation would have appeared had an on-table radiograph been taken intra-operatively. The mean difference between radiographic and intra-operative inclination/anteversion was 5° (sd 5°)/ -8° (sd 8°). The mean difference between simulated radiographic and intra-operative inclination/anteversion, which quantifies the effect of the different way acetabular orientation is measured, was 3°/-6° (sd 2°). The mean difference between radiographic and simulated radiographic orientation inclination/anteversion, which is a manifestation of the change in pelvic position between component impaction and radiograph, was 1°/-2° (sd 7°). This study demonstrated that in order to achieve a specific radiographic orientation target, surgeons should implant the acetabular component 5° less inclined and 8° more anteverted than their target. Great variability (2 sd about ± 15°) in the post-operative radiographic cup orientation was seen. The two equally contributing causes for this are variability in the orientation at which the cup is implanted, and the change in pelvic position between impaction and post-operative radiograph. ©2014 The British Editorial Society of Bone & Joint Surgery.

Application of an innovative computerized virtual planning system in acetabular fracture surgery: A feasibility study.

PubMed

Wang, Huixiang; Wang, Fang; Newman, Simon; Lin, Yanping; Chen, Xiaojun; Xu, Lu; Wang, Qiugen

2016-08-01

Acetabular fracture surgery is amongst the most challenging tasks in the field of trauma surgery and careful preoperative planning is crucial for success. The aim of this paper is to describe the preliminary outcome of the utilization of an innovative computerized virtual planning system for acetabular fractures. 3D models of acetabular fractures and surrounding soft tissues from six patients were constructed from preoperative CT scans. A novel highly-automatic segmentation technique was performed on the 3D model to separate each fracture fragment, then 3D virtual reduction was performed. Additionally, the models were used to assess potential surgical approaches with reference to both the fracture and the surrounding soft tissues. The time required for virtual planning was recorded. After surgery, the virtual plan was compared to the real surgery with respect to surgical approach and reduction sequence. A Likert scale questionnaire was completed by the surgeons to evaluate their satisfaction with the system. Virtual planning was successfully completed in all cases. The planned surgical approach was followed in all cases with the planned reduction sequence followed completely in five cases and partially in one. The mean time required for virtual planning was 38.7min (range 21-57, SD=15.5). The mean time required for planning of B-type fractures was 25.0min (range 21-30, SD=4.6), of C-type fracture 52.3min (range 49-57, SD=4.2). The results of the questionnaire demonstrated a high level of satisfaction with the planning system. This study demonstrates that the virtual planning system is feasible in clinical settings with high satisfaction and acceptability from the surgeons. It provides a viable option for the planning of acetabular fracture surgery. Copyright © 2016 Elsevier Ltd. All rights reserved.

Does semi-automatic bone-fragment segmentation improve the reproducibility of the Letournel acetabular fracture classification?

PubMed

Boudissa, M; Orfeuvre, B; Chabanas, M; Tonetti, J

2017-09-01

The Letournel classification of acetabular fracture shows poor reproducibility in inexperienced observers, despite the introduction of 3D imaging. We therefore developed a method of semi-automatic segmentation based on CT data. The present prospective study aimed to assess: (1) whether semi-automatic bone-fragment segmentation increased the rate of correct classification; (2) if so, in which fracture types; and (3) feasibility using the open-source itksnap 3.0 software package without incurring extra cost for users. Semi-automatic segmentation of acetabular fractures significantly increases the rate of correct classification by orthopedic surgery residents. Twelve orthopedic surgery residents classified 23 acetabular fractures. Six used conventional 3D reconstructions provided by the center's radiology department (conventional group) and 6 others used reconstructions obtained by semi-automatic segmentation using the open-source itksnap 3.0 software package (segmentation group). Bone fragments were identified by specific colors. Correct classification rates were compared between groups on Chi 2 test. Assessment was repeated 2 weeks later, to determine intra-observer reproducibility. Correct classification rates were significantly higher in the "segmentation" group: 114/138 (83%) versus 71/138 (52%); P<0.0001. The difference was greater for simple (36/36 (100%) versus 17/36 (47%); P<0.0001) than complex fractures (79/102 (77%) versus 54/102 (53%); P=0.0004). Mean segmentation time per fracture was 27±3min [range, 21-35min]. The segmentation group showed excellent intra-observer correlation coefficients, overall (ICC=0.88), and for simple (ICC=0.92) and complex fractures (ICC=0.84). Semi-automatic segmentation, identifying the various bone fragments, was effective in increasing the rate of correct acetabular fracture classification on the Letournel system by orthopedic surgery residents. It may be considered for routine use in education and training. III: prospective

Morphological experimental study of bone stress at the interface acetabular bone/prosthetic cup in the bipolar hip prosthesis.

PubMed

Anuşca, D; Pleşea, I E; Iliescu, N; Tomescu, P; Poenaru, F; Dascălu, V; Pop, O T

2006-01-01

By calculating the tension and distortion of the elements composing the bipolar prosthesis under extreme conditions encountered in real life using a special post-processing program, we established the variation curves of the contact pressure at the hip bone-cup, armor-cup and cup-femoral head interface. By comparing the data obtained from all the examined cases, important conclusions were drawn regarding the influence of tension and pressure distribution on the structural integrity and biomechanics of the prosthesis, as well as the acetabular wear and tear, in order to assess its reliability. The experimentally determined tension and distortion status at the acetabular bone-metal armour interface, lead to the wear and tear phenomenon, which can be explained by three mechanisms and theories incompletely reflecting the overall process. The histopathologic study of the acetabular bone tissue using FEM (finite elements method) on surgically removed specimens will probably lead to the identification of a series of factors that could reduce the rate of the wear and tear process.

Perioperative and acute care outcomes in morbidly obese patients with acetabular fractures at a Level 1 trauma center

PubMed Central

Vincent, Heather K.; Haupt, Edward; Tang, Sonya; Egwuatu, Adaeze; Vlasak, Richard; Horodyski, MaryBeth; Carden, Donna; Sadisivan, Kalia K.

2014-01-01

Background Controversy exists regarding obesity-related injury severity and clinical outcomes after orthopedic trauma. Purpose The purposes of this study were to expand our understanding of the effect of morbid obesity on perioperative and acute care outcomes after acetabular fracture. Methods This was a retrospective review of patients with acetabular fracture after trauma. Non-morbidly obese (BMI < 35 kg/m2) and morbidly obese (BMI ≥ 35 kg/m2; N = 81). Injury severity scores and Glasgow Coma Scale scores (GCS) were collected. Perioperative and acute care outcomes were positioning and operative time, extra fractures, estimated blood loss, complications, hospital charges, ventilator days, transfusions, length of stay (LOS) and discharge destination. Positioning and operative times were longer in morbidly obese patients (p < 0.05). No other differences existed between groups. Conclusions Orthopedic trauma surgeons and care teams can expect similar acute care outcomes in morbidly obese and non-morbidly obese patients with acetabular fracture. PMID:25104886

T2* Mapping Provides Information That Is Statistically Comparable to an Arthroscopic Evaluation of Acetabular Cartilage.

PubMed

Morgan, Patrick; Nissi, Mikko J; Hughes, John; Mortazavi, Shabnam; Ellerman, Jutta

2017-07-01

Objectives The purpose of this study was to validate T2* mapping as an objective, noninvasive method for the prediction of acetabular cartilage damage. Methods This is the second step in the validation of T2*. In a previous study, we established a quantitative predictive model for identifying and grading acetabular cartilage damage. In this study, the model was applied to a second cohort of 27 consecutive hips to validate the model. A clinical 3.0-T imaging protocol with T2* mapping was used. Acetabular regions of interest (ROI) were identified on magnetic resonance and graded using the previously established model. Each ROI was then graded in a blinded fashion by arthroscopy. Accurate surgical location of ROIs was facilitated with a 2-dimensional map projection of the acetabulum. A total of 459 ROIs were studied. Results When T2* mapping and arthroscopic assessment were compared, 82% of ROIs were within 1 Beck group (of a total 6 possible) and 32% of ROIs were classified identically. Disease prediction based on receiver operating characteristic curve analysis demonstrated a sensitivity of 0.713 and a specificity of 0.804. Model stability evaluation required no significant changes to the predictive model produced in the initial study. Conclusions These results validate that T2* mapping provides statistically comparable information regarding acetabular cartilage when compared to arthroscopy. In contrast to arthroscopy, T2* mapping is quantitative, noninvasive, and can be used in follow-up. Unlike research quantitative magnetic resonance protocols, T2* takes little time and does not require a contrast agent. This may facilitate its use in the clinical sphere.

Acetabular revision with impaction bone grafting and a cemented polyethylene acetabular component: comparison of the Kaplan-Meier analysis to the competing risk analysis in 62 revisions with 25 to 30 years follow-up.

PubMed

Te Stroet, M A J; Keurentjes, J C; Rijnen, W H C; Gardeniers, J W M; Verdonschot, N; Slooff, T J J H; Schreurs, B W

2015-10-01

We present the results of 62 consecutive acetabular revisions using impaction bone grafting and a cemented polyethylene acetabular component in 58 patients (13 men and 45 women) after a mean follow-up of 27 years (25 to 30). All patients were prospectively followed. The mean age at revision was 59.2 years (23 to 82). We performed Kaplan-Meier (KM) analysis and also a Competing Risk (CR) analysis because with long-term follow-up, the presence of a competing event (i.e. death) prevents the occurrence of the endpoint of re-revision. A total of 48 patients (52 hips) had died or had been re-revised at final review in March 2011. None of the deaths were related to the surgery. The mean Harris hip score of the ten surviving hips in ten patients was 76 points (45 to 99). The KM survivorship at 25 years for the endpoint 're-revision for any reason' was 58.0% (95% confidence interval (CI) 38 to 73) and for 're-revision for aseptic loosening' 72.1% (95% CI 51 to 85). With the CR analysis we calculated the KM analysis overestimates the failure rate with respectively 74% and 93% for these endpoints. The current study shows that acetabular impaction bone grafting revisions provide good clinical results at over 25 years. ©2015 The British Editorial Society of Bone & Joint Surgery.

High complication rate in reconstruction of Paprosky type IIIa acetabular defects using an oblong implant with modular side plates and a hook.

PubMed

Babis, G C; Sakellariou, V I; Chatziantoniou, A N; Soucacos, P N; Megas, P

2011-12-01

We report the results of 62 hips in 62 patients (17 males, 45 females) with mean age of 62.4 years (37 to 81), who underwent revision of the acetabular component of a total hip replacement due to aseptic loosening between May 2003 and November 2007. All hips had a Paprosky type IIIa acetabular defect. Acetabular revision was undertaken using a Procotyl E cementless oblong implant with modular side plates and a hook combined with impaction allografting. At a mean follow-up of 60.5 months (36 to 94) with no patients lost to follow-up and one died due to unrelated illness, the complication rate was 38.7%. Complications included aseptic loosening (19 hips), deep infection (3 hips), broken hook and side plate (one hip) and a femoral nerve palsy (one hip). Further revision of the acetabular component was required in 18 hips (29.0%) and a further four hips (6.4%) are currently loose and awaiting revision. We observed unacceptably high rates of complication and failure in our group of patients and cannot recommend this implant or technique.

Managing acetabular fractures in the elderly with fixation and primary arthroplasty: aiming for early weightbearing.

PubMed

Rickman, Mark; Young, James; Trompeter, Alex; Pearce, Rachel; Hamilton, Mark

2014-11-01

Osteoporotic acetabular fractures in the elderly are becoming more common. Regardless of treatment, most patients are managed with a period of protected weightbearing, even if a THA has been performed. We have tried to treat these patients analogously to geriatric femoral neck fractures in a way that allows immediate full weightbearing. We determined return to mobility, length of hospital stay (LOS), radiographic outcomes, and complications in a series of elderly osteoporotic patients treated for acetabular fractures with early fracture fixation and simultaneous THA, allowing full weightbearing immediately postoperatively. Since 2009, one surgeon (MR) used a consistent approach for fracture fixation and THA with immediate weightbearing in all patients older than 65 years with acetabular fractures who were fit for surgery and whose injuries were deemed osteoporotic fractures (low-energy mechanisms) meeting particular radiographic criteria (significant marginal impaction or femoral head damage). Twenty-four patients met these criteria and were reviewed at a mean of 24 months (range, 8-38 months). Mean age was 77 years (range, 63-90 years), and eight patients were women. The surgical technique included plate stabilization of both acetabular columns plus simultaneous THA using a tantalum socket and a cemented femoral stem. Clinical and note reviews were conducted to ascertain return to mobility, LOS, and postoperative complications. Component migration and fracture healing were assessed on plain radiographs. All patients mobilized with full weightbearing by Day 7 postoperatively. Only one patient remained dependent on a frame to mobilize at discharge. At 6 weeks, two patients already required no walking aids. At 6 months, patients were using a single stick at home at most, and all patients had managed stairs. Mean LOS was 18 days (range, 10-36 days). Radiographically, no component migration was seen in any patient. Seventeen of 24 fractures (71%) healed

Use of iPhone technology in improving acetabular component position in total hip arthroplasty.

PubMed

Tay, Xiau Wei; Zhang, Benny Xu; Gayagay, George

2017-09-01

Improper acetabular cup positioning is associated with high risk of complications after total hip arthroplasty. The aim of our study is to objectively compare 3 methods, namely (1) free hand, (2) alignment jig (Sputnik), and (3) iPhone application to identify an easy, reproducible, and accurate method in improving acetabular cup placement. We designed a simple setup and carried out a simple experiment (see Method section). Using statistical analysis, the difference in inclination angles using iPhone application compared with the freehand method was found to be statistically significant ( F [2,51] = 4.17, P = .02) in the "untrained group". There is no statistical significance detected for the other groups. This suggests a potential role for iPhone applications in junior surgeons in overcoming the steep learning curve.

Examination and treatment of a professional ballet dancer with a suspected acetabular labral tear: A case report.

PubMed

Khoo-Summers, Lynnette; Bloom, Nancy J

2015-08-01

Dancers are at risk for developing groin pain that is due to acetabular labral tears. Although surgical management of labral tears has been reported extensively, conservative management has been poorly described. This case report describes the examination, diagnosis, and treatment of groin pain in a professional ballet dancer with a suspected acetabular labral tear. Treatment focused on decreasing anterior hip joint stresses and improving the precision of hip motion through correction of alignment and movement impairments noted during functional activities and dance. Successful outcomes included a reduction in pain and return to professional ballet dancing. Copyright © 2015 Elsevier Ltd. All rights reserved.

21 CFR 888.3370 - Hip joint (hemi-hip) acetabular metal cemented prosthesis.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Hip joint (hemi-hip) acetabular metal cemented prosthesis. 888.3370 Section 888.3370 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3370 Hip joint...

21 CFR 888.3370 - Hip joint (hemi-hip) acetabular metal cemented prosthesis.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Hip joint (hemi-hip) acetabular metal cemented prosthesis. 888.3370 Section 888.3370 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3370 Hip joint...

21 CFR 888.3370 - Hip joint (hemi-hip) acetabular metal cemented prosthesis.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Hip joint (hemi-hip) acetabular metal cemented prosthesis. 888.3370 Section 888.3370 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3370 Hip joint...

Does surface roughness influence the primary stability of acetabular cups? A numerical and experimental biomechanical evaluation.

PubMed

Le Cann, Sophie; Galland, Alexandre; Rosa, Benoît; Le Corroller, Thomas; Pithioux, Martine; Argenson, Jean-Noël; Chabrand, Patrick; Parratte, Sébastien

2014-09-01

Most acetabular cups implanted today are press-fit impacted cementless. Anchorage begins with the primary stability given by insertion of a slightly oversized cup. This primary stability is key to obtaining bone ingrowth and secondary stability. We tested the hypothesis that primary stability of the cup is related to surface roughness of the implant, using both an experimental and a numerical models to analyze how three levels of surface roughness (micro, macro and combined) affect the primary stability of the cup. We also investigated the effect of differences in diameter between the cup and its substrate, and of insertion force, on the cups' primary stability. The results of our study show that primary stability depends on the surface roughness of the cup. The presence of macro-roughness on the peripheral ring is found to decrease primary stability; there was excessive abrasion of the substrate, damaging it and leading to poor primary stability. Numerical modeling indicates that oversizing the cup compared to its substrate has an impact on primary stability, as has insertion force. Copyright © 2014 IPEM. Published by Elsevier Ltd. All rights reserved.

Acetabular labral tears with underlying chondromalacia: a possible association with high-level running.

PubMed

Guanche, Carlos A; Sikka, Robby S

2005-05-01

The use of hip arthroscopy has helped delineate intra-articular pathology and has enabled clinicians to further elucidate the factors responsible for injuries, such as running. The subtle development of degenerative changes may be a result of repetitive impact loading associated with this sport. This study presents a population of runners with common pathologic acetabular changes. Case series. Eight high-level runners with an average age of 36 years (range, 19 to 45 years) were seen for complaints of increasing hip pain with running without any history of macrotrauma. All of the patients had either run several marathons (4), were triathletes (1), Olympic middle distance runners (1), or had run more than 10 miles per week for longer than 5 years (2). Plain radiographic analysis revealed no degenerative changes and an average center-edge (CE) angle of 36.7 degrees (range, 28 degrees to 44 degrees). All patients underwent hip arthroscopy with labral debridement. In 6 patients (75%), a chondral injury of the acetabular cartilage underlying the labral tear was noted. In addition, 3 patients had ligamentum teres disruptions. It is possible that the development of these tears is the result of subtle instability, which may be exacerbated by running, eventually leading to labral tearing and possible ligamentum teres disruption. While perhaps concurrently, subtle acetabular dysplasia may play a role. Although this study does not confirm an association between running and the development of labral tears or chondral lesions in the hip, it certainly questions whether there is an injury pattern common to this population, a "runner's hip." Level IV.

Combination acetabular radiofrequency ablation and cementoplasty using a navigational radiofrequency ablation device and ultrahigh viscosity cement: technical note.

PubMed

Wallace, Adam N; Huang, Ambrose J; Vaswani, Devin; Chang, Randy O; Jennings, Jack W

2016-03-01

Percutaneous radiofrequency ablation and cementoplasty is an alternative palliative therapy for painful metastases involving axial load-bearing bones. This technical report describes the use of a navigational radiofrequency probe to ablate acetabular metastases from an anterior approach followed by instillation of ultrahigh viscosity cement under CT-fluoroscopic guidance. The tumor ablation databases of two institutions were retrospectively reviewed to identify patients who underwent combination acetabular radiofrequency ablation and cementoplasty using the STAR Tumor Ablation and StabiliT Vertebral Augmentation Systems (DFINE; San Jose, CA). Pre-procedure acetabular tumor volume was measured on cross-sectional imaging. Pre- and post-procedure pain scores were measured using the Numeric Rating Scale (10-point scale) and compared. Partial pain improvement was categorically defined as ≥ 2-point pain score reduction. Patients were evaluated for evidence of immediate complications. Electronic medical records were reviewed for evidence of delayed complications. During the study period, 12 patients with acetabular metastases were treated. The median tumor volume was 54.3 mL (range, 28.3-109.8 mL). Pre- and post-procedure pain scores were obtained from 92% (11/12) of the cohort. The median pre-procedure pain score was 8 (range, 3-10). Post-procedure pain scores were obtained 7 days (82%; 9/11), 11 days (9.1%; 1/11) or 21 days (9.1%; 1/11) after treatment. The median post-treatment pain score was 3 (range, 1-8), a statistically significant difference compared with pre-treatment (P = 0.002). Categorically, 73% (8/11) of patients reported partial pain relief after treatment. No immediate symptomatic complications occurred. Three patients (25%; 3/12) were discharged to hospice within 1 week of treatment. No delayed complications occurred in the remaining 75% (9/12) of patients during median clinical follow-up of 62 days (range, 14-178 days). Palliative percutaneous

3D surgical printing and pre contoured plates for acetabular fractures.

PubMed

Chana-Rodríguez, Francisco; Mañanes, Rubén Pérez; Rojo-Manaute, José; Gil, Pablo; Martínez-Gómiz, José María; Vaquero-Martín, Javier

2016-11-01

We describe the methodical and possibilities of 3D surgical printing in preoperative planning of acetabular fractures showing a case of a 45-year-old with an associated transverse fracture of the left acetabulum with posterior wall fracture, with multiple fragments, and posterior ipsilateral hip dislocation, defending the do it your-self mode. Copyright © 2016 Elsevier Ltd. All rights reserved.

Reinforcements in avian wing bones: Experiments, analysis, and modeling.

PubMed

Novitskaya, E; Ruestes, C J; Porter, M M; Lubarda, V A; Meyers, M A; McKittrick, J

2017-12-01

Almost all species of modern birds are capable of flight; the mechanical competency of their wings and the rigidity of their skeletal system evolved to enable this outstanding feat. One of the most interesting examples of structural adaptation in birds is the internal structure of their wing bones. In flying birds, bones need to be sufficiently strong and stiff to withstand forces during takeoff, flight, and landing, with a minimum of weight. The cross-sectional morphology and presence of reinforcing structures (struts and ridges) found within bird wing bones vary from species to species, depending on how the wings are utilized. It is shown that both morphology and internal features increases the resistance to flexure and torsion with a minimum weight penalty. Prototypes of reinforcing struts fabricated by 3D printing were tested in diametral compression and torsion to validate the concept. In compression, the ovalization decreased through the insertion of struts, while they had no effect on torsional resistance. An elastic model of a circular ring reinforced by horizontal and vertical struts is developed to explain the compressive stiffening response of the ring caused by differently oriented struts. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effect of screw fixation on acetabular component alignment change in total hip arthroplasty.

PubMed

Fujishiro, Takaaki; Hayashi, Shinya; Kanzaki, Noriyuki; Hashimoto, Shingo; Shibanuma, Nao; Kurosaka, Masahiro

2014-06-01

The use of screws can enhance immediate cup fixation, but the influence of screw insertion on cup position has not previously been measured. The purpose of this study was to quantitatively evaluate the effect of intra-operative screw fixation on acetabular component alignment that has been inserted with the use of a navigation system. We used a navigation system to measure cup alignment at the time of press-fit and after screw fixation in 144 hips undergoing total hip arthroplasty. We also compared those findings with factors measured from postoperative radiographs. The mean intra-operative change of cup position was 1.78° for inclination and 1.81° for anteversion. The intra-operative change of anteversion correlated with the number of screws. The intra-operative change of inclination also correlated with medial hip centre. The insertion of screws can induce changes in cup alignment, especially when multiple screws are used or if a more medial hip centre is required for rigid acetabular fixation.

The development and nature of femoral head cam lesions following acetabular fractures.

PubMed

Berber, Onur; Foote, Julian; Sabharwal, Sanjeeve; Datta, Gorav; Bircher, Martin D

2014-01-01

The aim of acetabular fracture fixation is to restore joint congruity with restoration of the articular surface. Poor outcomes are seen where this has not been achieved. Letournel reported a collarette osteophyte seen postoperatively in a proportion of patients, which he suggested was an early precursor to the development of osteoarthritis. This is a retrospective study of patients treated at a tertiary referral unit who developed this lesion. The triangular index was measured in 48 of these patients and then correlated with their clinical findings, Oxford Hip Score and the presence of osteoarthritis. Length of follow-up, fracture classification, and joint congruency were also recorded. Results showed a statistically significant relationship between cam lesion size and the development of osteoarthritis (P = 0.008), cam lesion size and length of follow-up (P = 0.01), and between groin pain and postoperative joint congruency (LR = 0.035). These findings suggest that the appearance of a cam lesion is a poor long-term prognostic marker for the development of osteoarthritis in patients with an acetabular fracture.

A new approach for assessment of wear in metal-backed acetabular cups using computed tomography: a phantom study with retrievals.

PubMed

Jedenmalm, Anneli; Noz, Marilyn E; Olivecrona, Henrik; Olivecrona, Lotta; Stark, Andre

2008-04-01

Polyethylene wear is an important cause of aseptic loosening in hip arthroplasty. Detection of significant wear usually happens late on, since available diagnostic techniques are either not sensitive enough or too complicated and expensive for routine use. This study evaluates a new approach for measurement of linear wear of metal-backed acetabular cups using CT as the intended clinically feasible method. 8 retrieved uncemented metal-backed acetabular cups were scanned twice ex vivo using CT. The linear penetration depth of the femoral head into the cup was measured in the CT volumes using dedicated software. Landmark points were placed on the CT images of cup and head, and also on a reference plane in order to calculate the wear vector magnitude and angle to one of the axes. A coordinate-measuring machine was used to test the accuracy of the proposed CT method. For this purpose, the head diameters were also measured by both methods. Accuracy of the CT method for linear wear measurements was 0.6 mm and wear vector angle was 27 degrees . No systematic difference was found between CT scans. This study on explanted acetabular cups shows that CT is capable of reliable measurement of linear wear in acetabular cups at a clinically relevant level of accuracy. It was also possible to use the method for assessment of direction of wear.

Corrosion on the acetabular liner taper from retrieved modular metal-on-metal total hip replacements.

PubMed

Gascoyne, Trevor C; Dyrkacz, Richard M; Turgeon, Thomas R; Burnell, Colin D; Wyss, Urs P; Brandt, Jan-M

2014-10-01

Eight retrieved metal-on-metal total hip replacements displayed corrosion damage along the cobalt-chromium alloy liner taper junction with the Ti alloy acetabular shell. Scanning electron microscopy indicated the primary mechanism of corrosion to be grain boundary and associated crevice corrosion, which was likely accelerated through mechanical micromotion and galvanic corrosion resulting from dissimilar alloys. Coordinate measurements revealed up to 4.3mm(3) of the cobalt-chromium alloy taper surface was removed due to corrosion, which is comparable to previous reports of corrosion damage on head-neck tapers. The acetabular liner-shell taper appears to be an additional source of metal corrosion products in modular total hip replacements. Patients with these prostheses should be closely monitored for signs of adverse reaction towards corrosion by-products. Copyright © 2014 Elsevier Inc. All rights reserved.

Single-stage Acetabular Revision During Two-stage THA Revision for Infection is Effective in Selected Patients.

PubMed

Fink, Bernd; Schlumberger, Michael; Oremek, Damian

2017-08-01

The treatment of periprosthetic infections of hip arthroplasties typically involves use of either a single- or two-stage (with implantation of a temporary spacer) revision surgery. In patients with severe acetabular bone deficiencies, either already present or after component removal, spacers cannot be safely implanted. In such hips where it is impossible to use spacers and yet a two-stage revision of the prosthetic stem is recommended, we have combined a two-stage revision of the stem with a single revision of the cup. To our knowledge, this approach has not been reported before. (1) What proportion of patients treated with single-stage acetabular reconstruction as part of a two-stage revision for an infected THA remain free from infection at 2 or more years? (2) What are the Harris hip scores after the first stage and at 2 years or more after the definitive reimplantation? Between June 2009 and June 2014, we treated all patients undergoing surgical treatment for an infected THA using a single-stage acetabular revision as part of a two-stage THA exchange if the acetabular defect classification was Paprosky Types 2B, 2C, 3A, 3B, or pelvic discontinuity and a two-stage procedure was preferred for the femur. The procedure included removal of all components, joint débridement, definitive acetabular reconstruction (with a cage to bridge the defect, and a cemented socket), and a temporary cemented femoral component at the first stage; the second stage consisted of repeat joint and femoral débridement and exchange of the femoral component to a cementless device. During the period noted, 35 patients met those definitions and were treated with this approach. No patients were lost to followup before 2 years; mean followup was 42 months (range, 24-84 months). The clinical evaluation was performed with the Harris hip scores and resolution of infection was assessed by the absence of clinical signs of infection and a C-reactive protein level less than 10 mg/L. All

7. Detail view of reinforced concrete archrings comprising dam's upstream ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

7. Detail view of reinforced concrete arch-rings comprising dam's upstream face. Impressions of the wooden formwork used in construction are visible in the concrete. - Little Rock Creek Dam, Little Rock Creek, Littlerock, Los Angeles County, CA

Computed tomography image-guided surgery in complex acetabular fractures.

PubMed

Brown, G A; Willis, M C; Firoozbakhsh, K; Barmada, A; Tessman, C L; Montgomery, A

2000-01-01

Eleven complex acetabular fractures in 10 patients were treated by open reduction with internal fixation incorporating computed tomography image guided software intraoperatively. Each of the implants placed under image guidance was found to be accurate and without penetration of the pelvis or joint space. The setup time for the system was minimal. Accuracy in the range of 1 mm was found when registration was precise (eight cases) and was in the range of 3.5 mm when registration was only approximate (three cases). Added benefits included reduced intraoperative fluoroscopic time, less need for more extensive dissection, and obviation of additional surgical approaches in some cases. Compared with a series of similar fractures treated before this image guided series, the reduction in operative time was significant. For patients with complex anterior and posterior combined fractures, the average operation times with and without application of three-dimensional imaging technique were, respectively, 5 hours 15 minutes and 6 hours 14 minutes, revealing 16% less operative time for those who had surgery using image guidance. In the single column fracture group, the operation time for those with three-dimensional imaging application, was 2 hours 58 minutes and for those with traditional surgery, 3 hours 42 minutes, indicating 20% less operative time for those with imaging modality. Intraoperative computed tomography guided imagery was found to be an accurate and suitable method for use in the operative treatment of complex acetabular fractures with substantial displacement.

Treatment of acetabular fractures in older patients-introduction of a new implant for primary total hip arthroplasty.

PubMed

Resch, H; Krappinger, D; Moroder, P; Auffarth, A; Blauth, M; Becker, J

2017-04-01

Fractures of the acetabulum in younger patients are commonly treated by open reduction and internal fixation. For elderly patients, stable primary total hip arthroplasty with the advantage of immediate postoperative mobilization might be the adequate treatment. For this purpose, a sufficiently stable fixation of the acetabular component is required. Between August 2009 and 2014, 30 cases were reported in which all patients underwent total hip arthroplasty additionally to a customized implant designed as an antiprotrusion cage. Inclusion criteria were an acetabular fracture with or without a previous hemiarthroplasty, age above 65 years, and pre-injury mobility dependent on a walking frame at the most. The median age was 79.9 years (65-92), and of 30 fractures, 25 were primary acetabular fractures (83%), four periprosthetic acetabular fractures (14%), and one non-union after a failed ORIF (3%). The average time from injury to surgery was 9.4 days (3-23) and 295 days for the non-union case. Mean time of surgery was 154.4 min (range 100 to 303). In 21 cases (70%), mobilization with full weight bearing was possible within the first 10 days. Six patients died before the follow-up examination 3 and 6 months after surgery, while 24 patients underwent radiologic examination showing consolidated fractures in bi-plane radiographs. In 9 patients, additional CT scan was performed which confirmed the radiographical results. 13 had regained their pre-injury level of mobility including the non-union case. Only one patient did not regain independent mobility. Four complications were recognized with necessary surgical revision (one prosthetic head dislocation, one pelvic cement leakage, one femoral shaft fracture, and one infected hematoma). The presented cage provides the possibility of early mobilization with full weight bearing which represents a valuable addition to the treatment spectrum in this challenging patient group.

Variation in Treatment of Displaced Geriatric Acetabular Fractures Among 15 Level-I Trauma Centers.

PubMed

Manson, Theodore T; Reider, Lisa; OʼToole, Robert V; Scharfstein, Daniel O; Tornetta, Paul; Gary, Joshua L

2016-09-01

To document the initial treatment of displaced acetabular fractures among older adults across multiple trauma centers and to investigate the factors that influence the decision to operate and the choice of operative procedure [open reduction internal fixation (ORIF) vs. total hip arthroplasty (THA)]. Retrospective observational study. Fifteen US level-I trauma centers participating in the Major Extremity Trauma Research Consortium. Overall, 269 patients aged 60 years or older admitted for the treatment of a displaced acetabular fracture. None. Treatment. Sixty percent of fractures (n = 162) were treated operatively. Younger age (<80 years), injury from high-energy mechanism, fractures with femoral head impaction, and fractures without hip congruency were significantly associated with receiving operative treatment (P < 0.05). Significant site variation in operative versus nonoperative treatment occurred even after accounting for these factors (P = 0.0044). Among operatively treated patients, 88% (n = 142) received ORIF and 12% (n = 20) received THA as the initial treatment. Women were more likely to be treated with initial THA compared with men; of the known risk factors for poor outcomes with ORIF (ie, dome or roof impaction, femoral head impaction, or posterior wall involvement), only dome impaction was significantly associated with receiving initial THA (P < 0.05). Currently, no treatment guidelines exist for acetabular fractures in older adults, which likely explains the significant site variation in operative versus nonoperative treatment. This study identifies patient and injury factors that drive treatment decisions, which will be important in planning and designing future trials needed to determine the best treatment for these fractures.

Computer-aided designed, three dimensional-printed hemipelvic prosthesis for peri-acetabular malignant bone tumour.

PubMed

Wang, Baichuan; Hao, Yongqiang; Pu, Feifei; Jiang, Wenbo; Shao, Zengwu

2018-03-01

Prosthetic reconstruction may be a promising treatment for peri-acetabular malignant bone tumour; however, it is associated with a high complication rate. Therefore, prosthetic design and approach of prosthetic reconstruction after tumour resection warrant study. We retrospectively analyzed 11 patients with peri-acetabular malignant bone tumours treated by personalized 3D-printed hemipelvic prostheses after en bloc resection between 2015 and 2016. Pre-operative and post-operative pain at rest was assessed according to a 10-cm VAS score. The results of functional improvement were evaluated using the MSTS-93 score at the final follow-up. We also analyzed tumour recurrence, metastases, and complications associated with the reconstruction procedure. All patients were observed for six to 24 months with an average follow-up of 15.5 months. One patient had occasional pain of the involved hip at the final follow-up (VAS, pre vs. post 8 months: 3 vs. 2). The mean MSTS-93 score was 19.2 (range, 13-25). Hip dislocation was detected in two patients, while delayed wound healing occurred in one patient. One patient with mesenchymal chondrosarcoma had a left iliac bone metastasis. Local tumour recurrence was not observed. Reconstruction of bony defect after tumour resection using personalized 3D-printed hemipelvic prostheses can obtain acceptable functional results without severe complications. Based on previous reports and our results, we believe that reconstruction arthroplasty using 3D-printed hemipelvic prostheses will provide a promising alternative for those patients with peri-acetabular malignant bone tumours. Level IV, therapeutic study.

Does the optimal position of the acetabular fragment should be within the radiological normal range for all developmental dysplasia of the hip? A patient-specific finite element analysis.

PubMed

Wang, Xuyi; Peng, Jianping; Li, De; Zhang, Linlin; Wang, Hui; Jiang, Leisheng; Chen, Xiaodong

2016-10-04

The success of Bernese periacetabular osteotomy depends significantly on how extent the acetabular fragment can be corrected to its optimal position. This study was undertaken to investigate whether correcting the acetabular fragment into the so-called radiological "normal" range is the best choice for all developmental dysplasia of the hip with different severities of dysplasia from the biomechanical view? If not, is there any correlation between the biomechanically optimal position of the acetabular fragment and the severity of dysplasia? Four finite element models with different severities of dysplasia were developed. The virtual periacetabular osteotomy was performed with the acetabular fragment rotated anterolaterally to incremental center-edge angles; then, the contact area and pressure and von Mises stress in the cartilage were calculated at different correction angles. The optimal position of the acetabular fragment for patients 1, 2, and 3 was when the acetabular fragment rotated 17° laterally (with the lateral center-edge angle of 36° and anterior center-edge angle of 58°; both were slightly larger than the "normal" range), 25° laterally following further 5° anterior rotation (with the lateral center-edge angle of 31° and anterior center-edge angle of 51°; both were within the "normal" range), and 30° laterally following further 10° anterior rotation (with the lateral center-edge angle of 25° and anterior center-edge angle of 40°; both were less than the "normal" range), respectively. The optimal corrective position of the acetabular fragment is severity dependent rather than within the radiological "normal" range for developmental dysplasia of the hip. We prudently proposed that the optimal correction center-edge angle of mild, moderate, and severe developmental dysplasia of the hip is slightly larger than the "normal" range, within the "normal" range, and less than the lower limit of the "normal" range, respectively.

Mechanobiological simulations of peri-acetabular bone ingrowth: a comparative analysis of cell-phenotype specific and phenomenological algorithms.

PubMed

Mukherjee, Kaushik; Gupta, Sanjay

2017-03-01

Several mechanobiology algorithms have been employed to simulate bone ingrowth around porous coated implants. However, there is a scarcity of quantitative comparison between the efficacies of commonly used mechanoregulatory algorithms. The objectives of this study are: (1) to predict peri-acetabular bone ingrowth using cell-phenotype specific algorithm and to compare these predictions with those obtained using phenomenological algorithm and (2) to investigate the influences of cellular parameters on bone ingrowth. The variation in host bone material property and interfacial micromotion of the implanted pelvis were mapped onto the microscale model of implant-bone interface. An overall variation of 17-88 % in peri-acetabular bone ingrowth was observed. Despite differences in predicted tissue differentiation patterns during the initial period, both the algorithms predicted similar spatial distribution of neo-tissue layer, after attainment of equilibrium. Results indicated that phenomenological algorithm, being computationally faster than the cell-phenotype specific algorithm, might be used to predict peri-prosthetic bone ingrowth. The cell-phenotype specific algorithm, however, was found to be useful in numerically investigating the influence of alterations in cellular activities on bone ingrowth, owing to biologically related factors. Amongst the host of cellular activities, matrix production rate of bone tissue was found to have predominant influence on peri-acetabular bone ingrowth.

How Reliable is the Acetabular Cup Position Assessment from Routine Radiographs?

PubMed Central

Carvajal Alba, Jaime A.; Vincent, Heather K.; Sodhi, Jagdeep S.; Latta, Loren L.; Parvataneni, Hari K.

2017-01-01

Abstract Background: Cup position is crucial for optimal outcomes in total hip arthroplasty. Radiographic assessment of component position is routinely performed in the early postoperative period. Aims: The aims of this study were to determine in a controlled environment if routine radiographic methods accurately and reliably assess the acetabular cup position and to assess if there is a statistical difference related to the rater’s level of training. Methods: A pelvic model was mounted in a spatial frame. An acetabular cup was fixed in different degrees of version and inclination. Standardized radiographs were obtained. Ten observers including five fellowship-trained orthopaedic surgeons and five orthopaedic residents performed a blind assessment of cup position. Inclination was assessed from anteroposterior radiographs of the pelvis and version from cross-table lateral radiographs of the hip. Results: The radiographic methods used showed to be imprecise specially when the cup was positioned at the extremes of version and inclination. An excellent inter-observer reliability (Intra-class coefficient > 0,9) was evidenced. There were no differences related to the level of training of the raters. Conclusions: These widely used radiographic methods should be interpreted cautiously and computed tomography should be utilized in cases when further intervention is contemplated. PMID:28852355

[Charnley-type total hip prosthesis. Radiological technic of angular measurements of the acetabular piece (anteversion)].

PubMed

Chevrot, A; Najman, G

1983-01-01

A radiological technique is described based on the study of antero-posterior and lateral views of the hip. Mathematical calculations by trigonometry make it possible to deduce the degree of anteversion of the acetabular cup. The necessary tables are given.

[Stress analysis on the acetabular side of bipolar hemiarthroplasty by the two-dimensional finite element method incorporating the boundary friction layer].

PubMed

Ichihashi, K; Imura, S; Oomori, H; Gesso, H

1994-11-01

We compared the biomechanical characteristics of bipolar and unipolar hemiarthroplasty on the proximal migration of the outer head by determining the von Mises stress distribution and acetabular (outer head) displacement with clinical assessment of hemiarthroplasty in 75 patients. This analysis used the two-dimensional finite element method, which incorporated boundary friction layers on both the inner and outer bearings of the prosthesis. Acetabular reaming increased stress within the pelvic bone and migration of the outer head. A combination of the acetabular reaming and bone transplantation increased the stress within the pelvic bone and grafted bone, and caused outer head migration. These findings were supported by clinical results. Although the bipolar endoprosthesis was biomechanically superior to the unipolar endoprosthesis, migration of the outer head still occurred. The bipolar endoprosthesis appeared to be indicated in cases of a femoral neck fracture or of avascular necrosis in the femoral head, but its use in cases of osteoarthritis in the hip required caution.

Fluorocarbon seal replaces metal piston ring in low density gas environment

NASA Technical Reports Server (NTRS)

Morath, W. D.; Morgan, N. E.

1967-01-01

Reinforced fluorocarbon cupseal, which provides an integral lip-type seal, replaces the metal piston rings in piston-cylinder configurations used in the compression of low density gases. The fluorocarbon seal may be used as cryogenic compressor piston seals.

21 CFR 888.3330 - Hip joint metal/metal semi-constrained, with an uncemented acetabular component, prosthesis.

Code of Federal Regulations, 2010 CFR

2010-04-01

... component is intended to be fixed with bone cement. The acetabular component is intended for use without bone cement (§ 888.3027). (b) Classification. Class III. (c) Date PMA or notice of completion of a PDP...

21 CFR 888.3330 - Hip joint metal/metal semi-constrained, with an uncemented acetabular component, prosthesis.

Code of Federal Regulations, 2011 CFR

2011-04-01

... component is intended to be fixed with bone cement. The acetabular component is intended for use without bone cement (§ 888.3027). (b) Classification. Class III. (c) Date PMA or notice of completion of a PDP...

21 CFR 888.3330 - Hip joint metal/metal semi-constrained, with an uncemented acetabular component, prosthesis.

Code of Federal Regulations, 2012 CFR

2012-04-01

... component is intended to be fixed with bone cement. The acetabular component is intended for use without bone cement (§ 888.3027). (b) Classification. Class III. (c) Date PMA or notice of completion of a PDP...

21 CFR 888.3330 - Hip joint metal/metal semi-constrained, with an uncemented acetabular component, prosthesis.

Code of Federal Regulations, 2013 CFR

2013-04-01

... component is intended to be fixed with bone cement. The acetabular component is intended for use without bone cement (§ 888.3027). (b) Classification. Class III. (c) Date PMA or notice of completion of a PDP...

21 CFR 888.3330 - Hip joint metal/metal semi-constrained, with an uncemented acetabular component, prosthesis.

Code of Federal Regulations, 2014 CFR

2014-04-01

... component is intended to be fixed with bone cement. The acetabular component is intended for use without bone cement (§ 888.3027). (b) Classification. Class III. (c) Date PMA or notice of completion of a PDP...

The epidemiology and injury patterns of acetabular fractures: are the USA and China comparable?

PubMed

Mauffrey, Cyril; Hao, Jiandong; Cuellar, Derly O; Herbert, Benoit; Chen, Xiao; Liu, Bo; Zhang, Yingze; Smith, Wade

2014-11-01

Acetabular fractures are rare injuries in heterogeneous patient groups, making it difficult to develop adequately powered prospective single-center clinical trials in the USA or Europe. Chinese trauma centers treat a high volume of these injuries, and if the patient population and injury patterns are comparable to those in the USA, this might support development of multicenter studies in Level I trauma centers in the two countries. We determined whether the following parameters were similar between operative acetabular fractures treated at Chinese and US trauma centers: (1) epidemiology of injured patients, (2) mechanism of injuries and fracture types, and (3) hospital stay parameters, including symptomatic postoperative deep vein thrombosis (DVT) rate. We extracted data from trauma databases for patients admitted with acetabular fractures managed surgically from 2005 to 2012 for one Chinese center and from 2008 to 2012 for one US center. Sex, age, mechanism of injury, fracture classification, Injury Severity Score (ISS), time from injury to surgery, length of hospital stay, and symptomatic DVT rate were analyzed. We included 661 Chinese patients (539 men, 122 women) and 212 US patients (163 men, 49 women). Mean age at time of injury was different between China and the USA, at 40 years with a unimodal distribution and 44 years with a bimodal distribution (p<0.001), respectively. Incidence of surgically treated acetabular fractures has been increasing in China but decreasing in the USA. Mean ISSs were comparable. Although the distribution of mechanisms of injury was different (p=0.004), high-energy injuries (motor vehicle accidents, falls>10 feet) still accounted for most fractures in both centers. Fracture classifications (per Letournel) were comparable, with posterior wall fractures most common. Mean time from injury to surgery and mean hospital stay were longer in China than in the USA (9 versus 3 days [p<0.001] and 26 versus 11 days [p<0.001], respectively

Survivorship of the native hip joint after percutaneous repair of acetabular fractures in the elderly.

PubMed

Gary, Joshua L; Lefaivre, Kelly A; Gerold, Frank; Hay, Michael T; Reinert, Charles M; Starr, Adam J

2011-10-01

Our purpose was to examine survivorship of the native hip joint in patients ages 60 and over who underwent percutaneous reduction and fixation of acetabular fractures. A retrospective review at a University Level I Trauma Center was performed. Our institutional trauma database was reviewed. Patients aged 60 or older treated with percutaneous reduction and fixation of acetabular fractures between 1994 and 2007 were selected. 79 consecutive patients with 80 fractures were identified. Rate of conversion to total hip arthroplasty were used to construct a Kaplan-Meier curve showing survivorship of the native hip joint after treatment. 75 fractures had adequate clinical follow-up with a mean of 3.9 years (range 0.5-11.9 years). Average blood loss was 69 cc and there were no postoperative infections. 19/75 (25%) were converted to total hip arthroplasty at a mean time of 1.4 years after the index procedure. Survivorship analysis demonstrated a cumulative survival of 65% at 11.9 years of follow-up. There were no conversions to arthroplasty beyond 4.7 years postoperatively. There were no statistically significant associations between conversion to arthroplasty and age, sex, closed vs. limited open reduction, and simple vs. complex fracture pattern. Percutaneous fixation is a viable treatment option for patients age 60 or greater with acetabular fractures. Rates of conversion to total hip arthroplasty are comparable to open treatment methods and if conversion is required, soft tissues are preserved for future surgery. Copyright © 2010 Elsevier Ltd. All rights reserved.

[Acetabular anteversion angle of the hip in the Mexican adult population measured with computed tomography].

PubMed

Rubalcava, J; Gómez-García, F; Ríos-Reina, J L

2012-01-01

Knowledge of the radiogrametric characteristics of a specific skeletal segment in a healthy population is of the utmost clinical importance. The main justification for this study is that there is no published description of the radiogrametric parameter of acetabular anteversion in a healthy Mexican adult population. A prospective, descriptive and cross-sectional study was conducted. Individuals of both genders older than 18 years and orthopedically healthy were included. They underwent a two-dimensional axial tomographic study of both hips to measure the acetabular anteversion angles. The statistical analysis consisted of obtaining central trend and scatter measurements. A multivariate analysis of variance (ANOVA) and statistical significance were performed. 118 individuals were studied, 60 males and 58 females, with a mean age of 47.7 +/- 16.7, and a range of 18-85 years. The anteversion of the entire group was 18.6 degrees + 4.1 degrees. Anteversion in males was 17.3 degrees +/- 3.5 degrees (10 degrees - 25 degrees) and in females 19.8 degrees +/- 4.7 degrees (10 degrees - 31 degrees). There were no statistically significant differences (p < or = 0.05) in right and left anteversion in the entire group. However, there were statistically significant differences (p > or = 0.005) both in the right and left sides when males and females were compared. Our study showed that there are great variations in the anteversion ranges of a healthy population. When our results are compared with those published by other authors the mean of most measurements exceeds 15 degrees. This should be useful to make therapeutic decisions that involve acetabular anteversion.

Measuring acetabular component position on lateral radiographs - ischio-lateral method.

PubMed

Pulos, Nicholas; Tiberi Iii, John V; Schmalzried, Thomas P

2011-01-01

The standard method for the evaluation of arthritis and postoperative assessment of arthroplasty treatment is observation and measurement from plain films, using the flm edge for orientation. A more recent employment of an anatomical landmark, the ischial tuberosity, has come into use as orientation for evaluation and is called the ischio-lateral method. In this study, the use of this method was evaluated as a first report to the literature on acetabular component measurement using a skeletal reference with lateral radiographs. Postoperative radiographs of 52 hips, with at least three true lateral radiographs taken at different time periods, were analyzed. Component position was measured with the historical method (using the flm edge for orientation) and with the new method using the ischio-lateral method. The mean standard deviation (SD) for the historical approach was 3.7° and for the ischio-lateral method, 2.2° (p < 0.001). With the historical method, 19 (36.5%) hips had a SD greater than ± 4°, compared to six hips (11.5%) with the ischio-lateral method. By using a skeletal reference, the ischio-lateral method provides a more consistent measurement of acetabular component position. The high intra-class correlation coefficients for both intra- and inter-observer reliability indicate that the angle measured with this simple method, which employs no further technology, increased time, or cost, is consistent and reproducible for multiple observers.

[One-stage operation for pelvis and acetabular fractures combined with Morel-Lavallée injury by internal fixation associated with vacuum sealing drainage].

PubMed

Wei, Dan; Wang, Yue; Yuan, Jiabin; Tang, Xiaoming; Zhang, Bin; Lu, Bing; Tan, Bo

2014-01-01

To investigate the methods and effectiveness of one-stage operation for pelvis and acetabular fractures combined with Morel-Lavallée injury by internal fixation associated with vacuum sealing drainage (VSD). Between June 2008 and October 2012, 15 cases of pelvis and acetabular fractures combined with Morel-Lavallée injury were treated. There were 5 males and 10 females, aged from 18 to 67 years (mean, 36.8 years). Fractures were caused by traffic accident in 11 cases and crashing injury of heavy object in 4 cases. The time from injury to hospitalization was 3 hours to 9 days (mean, 5.4 days). Morel-Lavallée injury located in the above posterior superior iliac spine in 4 cases, greater trochanter in 7 cases, and anterior proximal thigh in 4 cases. In 10 cases complicated by pelvic fracture, there were 1 case of anteroposterior compression type, 3 cases of lateral compression type, 5 cases of vertical shear type, and 1 case of compound injury type; in 5 cases complicated by acetabular fracture, there were 1 case of transverse fracture, 1 case of posterior wall and posterior column fracture, 1 case of transverse acetabulum plus posterior wall fracture, and 2 cases of both columns fracture. Open reduction and internal fixation were used to treat pelvic and acetabular fractures, and VSD to treat Morel-Lavallée injury. When the drainage volume was less than 20 mL/d, interrupted wound suture or free skin grafting was performed. The hospitalization time was 16-31 days (mean, 20.8 days). Thirteen cases were followed up 4-16 months (mean, 7.8 months). The healing time of Morel-Lavallée injury was 16-36 days after operation (mean, 21.3 days). All the wounds had primary healing, and no infection occurred. The X-ray films showed that all fractures healed, with a mean healing time of 13.6 weeks (range, 11-18 weeks). At 6.5 months after operation, according to Majeed function scoring system in 8 cases of pelvic fracture, the results were excellent in 5 cases, good in 2 cases

Effect of acetabular cup abduction angle on wear of ultrahigh-molecular-weight polyethylene in hip simulator testing.

PubMed

Korduba, Laryssa A; Essner, Aaron; Pivec, Robert; Lancin, Perry; Mont, Michael A; Wang, Aiguo; Delanois, Ronald E

2014-10-01

The effect of acetabular component positioning on the wear rates of metal-on-polyethylene articulations has not been extensively studied. Placement of acetabular cups at abduction angles of more than 40° has been noted as a possible reason for early failure caused by increased wear. We conducted a study to evaluate the effects of different acetabular cup abduction angles on polyethylene wear rate, wear area, contact pressure, and contact area. Our in vitro study used a hip joint simulator and finite element analysis to assess the effects of cup orientation at 4 angles (0°, 40°, 50°, 70°) on wear and contact properties. Polyethylene bearings with 28-mm cobalt-chrome femoral heads were cycled in an environment mimicking in vivo joint fluid to determine the volumetric wear rate after 10 million cycles. Contact pressure and contact area for each cup abduction angle were assessed using finite element analysis. Results were correlated with cup abduction angles to determine if there were any differences among the 4 groups. The inverse relationship between volumetric wear rate and acetabular cup inclination angle demonstrated less wear with steeper cup angles. The largest abduction angle (70°) had the lowest contact area, largest contact pressure, and smallest head coverage. Conversely, the smallest abduction angle (0°) had the most wear and most head coverage. Polyethylene wear after total hip arthroplasty is a major cause of osteolysis and aseptic loosening, which may lead to premature implant failure. Several studies have found that high wear rates for cups oriented at steep angles contributed to their failure. Our data demonstrated that larger cup abduction angles were associated with lower, not higher, wear. However, this potentially "protective" effect is likely counteracted by other complications of steep cup angles, including impingement, instability, and edge loading. These factors may be more relevant in explaining why implants fail at a higher rate if

Early polyethylene wear and osteolysis with ABG acetabular cups (7- to 12-year follow-up).

PubMed

Badhe, Sachin; Livesley, Peter

2006-02-01

We reviewed 81 consecutive ABG I primary total hip replacements implanted in 72 patients between January 1993 and December 1998. The mean follow-up was 8.2 (range 7-12) years. There was significant polyethylene wear and osteolysis associated with the acetabular cup . The cumulative survival of the cup with revision being the end point at 8.2 years was 95.1% (95% CI: 92-97.6%). However, the cumulative survival of the cup with revision and aseptic loosening together was 72% (95% CI: 61-78%) and survival of the acetabular liner for wear was 62% (95% CI: 48-74%). Stem survival with revision being the end point was 100%. In spite of significant radiological failures of the cups, most patients remained asymptomatic. Though results of the ABG stems in this series were good, we advocate a regular follow-up of all these hips in view of the poor outcome of the cups.

Early polyethylene wear and osteolysis with ABG acetabular cups (7- to 12-year follow-up)

PubMed Central

Livesley, Peter

2005-01-01

We reviewed 81 consecutive ABG I primary total hip replacements implanted in 72 patients between January 1993 and December 1998. The mean follow-up was 8.2 (range 7–12) years. There was significant polyethylene wear and osteolysis associated with the acetabular cup .The cumulative survival of the cup with revision being the end point at 8.2 years was 95.1% (95% CI: 92–97.6%). However, the cumulative survival of the cup with revision and aseptic loosening together was 72% (95% CI: 61–78%) and survival of the acetabular liner for wear was 62% (95% CI: 48–74%). Stem survival with revision being the end point was 100%. In spite of significant radiological failures of the cups, most patients remained asymptomatic. Though results of the ABG stems in this series were good, we advocate a regular follow-up of all these hips in view of the poor outcome of the cups. PMID:16283307

The effect of variable size posterior wall acetabular fractures on contact characteristics of the hip joint.

PubMed

Olson, S A; Bay, B K; Pollak, A N; Sharkey, N A; Lee, T

1996-01-01

The indications for open reduction and internal fixation of posterior wall acetabular fractures associated with a clinically stable hip joint are unclear. In previous work a large posterior wall defect (27% articular surface area) resulted in significant alteration of load transmission across the hip; specifically, there was a transition from evenly distributed loading along the acetabular articular surface to loading concentrated mainly in the superior portion of the articular surface during simulated single leg stance. However, the majority of posterior wall fractures involve a smaller amount of the articular surface. Posterior wall acetabular fractures not associated with instability of the hip are commonly treated nonoperatively. This practice does not account for the size of the posterior wall fracture. To study the biomechanical consequences of variably sized articular defects, a laboratory experiment was conducted evaluating three progressively larger posterior wall defects of the acetabulum during simulated single leg stance using superlow Fuji prescale film (Itochu International, New York): (a) 1/3 articular surface width through a 50 degrees arc along the posterior wall of the acetabulum, (b) 2/3, and (c) 3/3 articular width defects through the same 50 degrees arc along the posterior wall of the acetabulum. In the intact acetabulum, 48% of the total articular contact was located in the superior acetabulum. Twenty-eight percent of articular contact was in the anterior wall region of the acetabulum and 24% in the posterior wall region. After the 1/3 width posterior wall defect, 64% of the articular contact was located in the superior acetabulum (p = 0.0011). The 2/3 width posterior wall defect resulted in 71% of articular contact area being located in the superior acetabulum (p = 0.0006). After the 3/3 width posterior wall defect, 77% of articular contact was located in the superior acetabulum, significantly greater than the intact condition (p < 0

Cup press fit in uncemented THA depends on sex, acetabular shape, and surgical technique.

PubMed

García-Rey, Eduardo; García-Cimbrelo, Eduardo; Cruz-Pardos, Ana

2012-11-01

Uncemented press-fit cups provide bone fixation in primary THA, but the use of screws is sometimes necessary to achieve primary stability of the socket. However, it is unclear whether and when screws should be used. We analyzed the factors related to screw use with a press-fit uncemented cup and assessed whether screw use is associated with the same rates of loosening and revision as a press-fit technique. We retrospectively reviewed 248 patients who underwent THA using the same prosthetic design. Eighty-eight hips had screws to achieve primary cup fixation (Group 1), and 189 did not (Group 2). Mean age was 50 years (range, 14-73 years). We analyzed factors related to the patient, acetabular type, and reconstruction of the rotation center of the hip. Minimum followup was 5 years (mean, 8.9 years; range, 5-12 years). We found higher screw use in women, patients with less physical activity, Acetabular Types A or C, and a distance from the center of the prosthetic femoral head to the normal center of rotation of more than 3 mm. There were four revisions in Group 1 and five in Group 2. Eight hips had radiographic loosening in Group 1 and nine in Group 2. Cups with a postoperative abduction angle of more than 50° had a higher risk for loosening. Press fit was achieved less frequently in women and patients with Acetabular Types A or C and less physical activity; a closer distance to the normal center of rotation decreased screw use. Screw use to augment fixation achieved survival similar to that of a press-fit cup. Level II, prognostic study. See Instructions for Authors for a complete description of levels of evidence.

Myofascial treatment for patients with acetabular labral tears: a single-subject research design study.

PubMed

Cashman, Glenn E; Mortenson, W Ben; Gilbart, Michael K

2014-08-01

Single-subject research design using 4 consecutive patients. To assess whether treatment using soft tissue therapy (ART or Active Release Technique), stretching, and strengthening of the hip abductors, hip external rotators, and tensor fascia latae muscles reduces pain and improves self-reported hip function in patients with acetabular labral tears who also have posterolateral hip pain of suspected myofascial origin. Acetabular labral tears cause pain in some but not all patients. Pain commonly presents anteriorly but may also present posteriorly and laterally. The standard of care is arthroscopic repair, which helps many but not all patients. It is possible that these patients may present with extra-articular contributions to their pain, such as myofascial pain, making their clinical presentation more complex. No previous study has assessed soft tissue therapy as a treatment option for this subset of patients. This A-B-A design used repeated measures of the Hip Outcome Score and visual analog scale for pain. Four patients were treated for 6 to 8 weeks, using a combination of soft tissue therapy, stretching, and strengthening for the hip abductors, external rotators, and tensor fascia latae. Data were assessed visually, statistically, and by comparing mean differences before and after intervention. All 4 patients experienced both statistically significant and clinically meaningful improvement in posterolateral hip pain and hip-related function. Three patients also experienced reduction in anteromedial hip pain. Myofascial hip pain may contribute to hip-related symptoms and disability in patients with acetabular labral tears and posterolateral hip pain. These patients may benefit from soft tissue therapy combined with stretching and strengthening exercises targeting the hip abductors, tensor fascia latae, and hip external rotator muscles. Level of Evidence Therapy, level 4.

Post-deformation shape-recovery behavior of vitamin E-diffused, radiation crosslinked polyethylene acetabular components.

PubMed

Takahashi, Yasuhito; Tateiwa, Toshiyuki; Shishido, Takaaki; Masaoka, Toshinori; Kubo, Kosuke; Yamamoto, Kengo

2016-10-01

The in-vivo progression of creep and wear in ultra-high molecular weight polyethylene (UHMWPE) acetabular liners has been clinically evaluated by measuring radiographic penetration of femoral heads. In such clinical assessments, however, viscoelastic strain relaxation has been rarely considered after a removal of hip joint loading, potentially leading to an underestimation of the penetrated thickness. The objective of this study was to investigate shape-recovery behavior of pre-compressed, radiation crosslinked and antioxidant vitamin E-diffused UHMWPE acetabular liners, and also to characterize the effects of varying their internal diameter (ID) and wall thickness (WT). We applied uniaxial compression to the UHMWPE specimens of various ID (28, 32, 36mm) and WT (4.8, 6.8, 8.9mm) for 4320min under the constant load of 3000N, and subsequently monitored the strain-relaxation behavior as a function of time after unloading. It was observed that there was a considerable shape recovery of the components after removal of the external static load. Reducing ID and WT significantly accelerated the rate of creep strain recovery, and varying WT was more sensitive to the recovery behavior than ID. Creep deformation of the tested liners recovered mostly within the first 300min after unloading. Note that approximately half of the total recovery amount proceeded just within 5min after unloading. These results suggest a remarkably high capability of shape recovery of vitamin E-diffused highly crosslinked UHMWPE. In conclusion, the time-dependent shape recovering and the diameter-thickness effect on its behavior should be carefully considered when the postoperative penetration is quantified in highly crosslinked UHMWPE acetabular liners (especially on the non-weight bearing radiographs). Copyright © 2016 Elsevier Ltd. All rights reserved.

Biocompatibility of Bespoke 3D-Printed Titanium Alloy Plates for Treating Acetabular Fractures.

PubMed

Lin, Xuezhi; Xiao, Xingling; Wang, Yimeng; Gu, Cheng; Wang, Canbin; Chen, Jiahui; Liu, Han; Luo, Juan; Li, Tao; Wang, Di; Fan, Shicai

2018-01-01

Treatment of acetabular fractures is challenging, not only because of its complicated anatomy but also because of the lack of fitting plates. Personalized titanium alloy plates can be fabricated by selective laser melting (SLM) but the biocompatibility of these three-dimensional printing (3D-printed) plates remains unknown. Plates were manufactured by SLM and their cytocompatibility was assessed by observing the metabolism of L929 fibroblasts incubated with culture medium extracts using a CCK-8 assay and their morphology by light microscopy. Allergenicity was tested using a guinea pig maximization test. In addition, acute systemic toxicity of the 3D-printed plates was determined by injecting extracts from the implants into the tail veins of mice. Finally, the histocompatibility of the plates was investigated by implanting them into the dorsal muscles of rabbits. The in vitro results suggested that cytocompatibility of the 3D-printed plates was similar to that of conventional plates. The in vivo data also demonstrated histocompatibility that was comparable between the two manufacturing techniques. In conclusion, both in vivo and in vitro experiments suggested favorable biocompatibility of 3D-printed titanium alloy plates, indicating that it is a promising option for treatment of acetabular fractures.

Promising Mid-term Results With a Cup-cage Construct for Large Acetabular Defects and Pelvic Discontinuity.

PubMed

Amenabar, Tomas; Rahman, Wael A; Hetaimish, Bandar M; Kuzyk, Paul R; Safir, Oleg A; Gross, Allan E

2016-02-01

Restoring normal anatomy and achieving stable fixation of the acetabular component can be especially challenging when the surgeon must deal with severe acetabular defects and/or pelvic discontinuity. The cup-cage (CC) construct, where an ilioischial cage is cemented within a biologically fixed porous metal cup, has emerged as an excellent option to treat such challenges. We sought to determine (1) mid-term Kaplan-Meier survival; (2) clinical outcomes based on Merle d'Aubigné-Postel scores; (3) radiological outcomes based primarily on construct migration; and (4) the complication rate for a series of 67 CC procedures performed at our institution. All hip revision procedures between January 2003 and March 2012 where a CC was used (with the exception of tumor cases or acute fracture; four total cases) that had a minimum 2-year followup and that had been seen within the last 2 years were included in this retrospective review. Acetabular bone loss and presence of pelvic discontinuity were assessed according to the Gross classification. Sixty-seven CC procedures with an average followup of 74 months (range, 24-135 months; SD, 34.3) months were identified; 26 of 67 (39%) were Gross Type IV and 41 of 67 (61%) were Gross Type V (pelvic discontinuity). Postoperative clinical and radiological evaluation was done annually. Merle d'Aubigné-Postel scores were recorded and all radiographs were compared with the 6-week postoperative radiographs to evaluate for radiographic loosening or migration. Failure was defined as revision surgery for any cause, including infection. The 5-year Kaplan-Meier survival rate with revision for any cause representing failure was 93% (95% confidence interval [CI], 83.1-97.4), and the 10-year survival rate was 85% (95% CI, 67.2-93.8). The Merle d'Aubigné-Postel score improved significantly from a mean of 6 preoperatively to 13 postoperatively (p < 0.001). Four CC had nonprogressive radiological migration of the ischial flange and they remain stable

Tribological characteristics of silicon carbide whisker-reinforced alumina at elevated temperatures

NASA Technical Reports Server (NTRS)

Dellacorte, Christopher

1991-01-01

The enhanced fracture toughness of whisker reinforced ceramics makes them attractive candidates for sliding components of advanced hear engines. Examples include piston rings and valve stems for Stirling engines and other low heat rejection devices. However, the tribological behavior of whisker reinforced ceramics is largely unknown. This is especially true for the applications described where use temperatures can vary from below ambient to well over 1000 C. An experimental research program to identify the dominant wear mechanism(s) for a silicon carbide whisker reinforced alumina composite, SiCw-Al2O3 is described. In addition, a wear mechanism model is developed to explain and corroborate the experimental results and to provide insight for material improvement.

Use of a constrained tripolar acetabular liner to treat intraoperative instability and postoperative dislocation after total hip arthroplasty: a review of our experience.

PubMed

Callaghan, John J; O'Rourke, Michael R; Goetz, Devon D; Lewallen, David G; Johnston, Richard C; Capello, William N

2004-12-01

Constrained acetabular components have been used to treat certain cases of intraoperative instability and postoperative dislocation after total hip arthroplasty. We report our experience with a tripolar constrained component used in these situations since 1988. The outcomes of the cases where this component was used were analyzed for component failure, component loosening, and osteolysis. At average 10-year followup, for cases treated for intraoperative instability (2 cases) or postoperative dislocation (4 cases), the component failure rate was 6% (6 of 101 hips in 5 patients). For cases where the constrained liner was cemented into a fixed cementless acetabular shell, the failure rate was 7% (2 of 31 hips in 2 patients) at 3.9-year average followup. Use of a constrained liner was not associated with an increased osteolysis or aseptic loosening rate. This tripolar constrained acetabular liner provided total hip arthroplasty construct stability in most cases in which it was used for intraoperative instability or postoperative dislocation.

Direct and indirect costs of surgically treated pelvic fractures.

PubMed

Aprato, Alessandro; Joeris, Alexander; Tosto, Ferdinando; Kalampoki, Vasiliki; Stucchi, Alessandro; Massè, Alessandro

2016-03-01

Pelvic fractures requiring surgical fixation are rare injuries but present a great societal impact in terms of disability, as well as economic resources. In the literature, there is no description of these costs. Main aim of this study is to describe the direct and indirect costs of these fractures. Secondary aims were to test if the type of fracture (pelvic ring injury or acetabular fracture) influences these costs (hospitalization, consultation, medication, physiotherapy sessions, job absenteeism). We performed a retrospective study on patients with surgically treated acetabular fractures or pelvic ring injuries. Medical records were reviewed in terms of demographic data, follow-up, diagnosis (according to Letournel and Tile classifications for acetabular and pelvic fractures, respectively) and type of surgical treatment. Patients were interviewed about hospitalization length, consultations after discharge, medications, physiotherapy sessions and absenteeism. The study comprised 203 patients, with a mean age of 49.1 ± 15.6 years, who had undergone surgery for an acetabular fracture or pelvic ring injury. The median treatment costs were 29.425 Euros per patient. Sixty percent of the total costs were attributed to health-related work absence. Median costs (in Euros) were 2.767 for hospitalization from trauma to definitive surgery, 4.530 for surgery, 3.018 for hospitalization in the surgical unit, 1.693 for hospitalization in the rehabilitation unit, 1.920 for physiotherapy after discharge and 402 for consultations after discharge. Total costs for treating pelvic ring injuries were higher than for acetabular fractures, mainly due to the significant higher costs of pelvic injuries regarding hospitalization from trauma to definitive surgery (p < 0.001) and hospitalization in the surgical unit (p = 0.008). Pelvic fractures are associated with both high direct costs and substantial productivity loss.

Usefulness of Arthroscopic Treatment of Painful Hip after Acetabular Fracture or Hip Dislocation.

PubMed

Hwang, Jung-Taek; Lee, Woo-Yong; Kang, Chan; Hwang, Deuk-Soo; Kim, Dong-Yeol; Zheng, Long

2015-12-01

Painful hip following hip dislocation or acetabular fracture can be an important signal for early degeneration and progression to osteoarthritis due to intraarticular pathology. However, there is limited literature discussing the use of arthroscopy for the treatment of painful hip. The purpose of this retrospective study was to analyze the effectiveness and benefit of arthroscopic treatment for patients with a painful hip after major trauma. From July 2003 to February 2013, we reviewed 13 patients who underwent arthroscopic treatment after acetabular fracture or hip dislocation and were followed up for a minimum of 2 postoperative years. The degree of osteoarthritis based on the Tonnis classification pre- and postoperatively at final follow-up was determined. Clinical outcomes were evaluated using visual analogue scale for pain (VAS) and modified Harris hip score (MHHS), and range of motion (ROM) of the hip pre- and postoperatively at final follow-up. There were nine male and four female patients with a mean age at surgery of 28 years (range, 20 to 50 years). The mean follow-up period of the patients was 59.8 months (range, 24 to 115 months), and the mean interval between initial trauma and arthroscopic treatment was 40.8 months (range, 1 to 144 months). At the final follow-up, VAS and MHHS improved significantly from 6.3 and 53.4 to 3.0 and 88.3, respectively (p = 0.002 and p < 0.001, respectively). However, there were no significant differences in hip flexion, abduction, adduction, external rotation, and internal rotation as minor improvements from 113.1°, 38.5°, 28.5°, 36.5°, and 22.7° to 118.5°, 39.0°, 29.2°, 38.9°, and 26.5° were observed, respectively (p = 0.070, p = 0.414, p = 0.317, p = 0.084, and p = 0.136, respectively). None of the patients exhibited progression of osteoarthritis of the hip at the final follow-up. Arthroscopic treatment after acetabular fracture or hip dislocation is effective and delays the progression of traumatic

[Correlation analysis between residual displacement and hip function after reconstruction of acetabular fractures].

PubMed

Ma, Kunlong; Fang, Yue; Luan, Fujun; Tu, Chongqi; Yang, Tianfu

2012-03-01

To investigate the relationships between residual displacement of weight-bearing and non weight-bearing zones (gap displacement and step displacement) and hip function by analyzing the CT images after reconstruction of acetabular fractures. The CT measures and clinical outcome were retrospectively analyzed from 48 patients with displaced acetabular fracture between June 2004 and June 2009. All patients were treated by open reduction and internal fixation, and were followed up 24 to 72 months (mean, 36 months); all fractures healed after operation. The residual displacement involved the weight-bearing zone in 30 cases (weight-bearing group), and involved the non weight-bearing zone in 18 cases (non weight-bearing group). The clinical outcomes were evaluated by Merle d'Aubigné-Postel criteria, and the reduction of articular surface by CT images, including the maximums of two indexes (gap displacement and step displacement). All the data were analyzed in accordance with the Spearman rank correlation coefficient analysis. There was strong negative correlation between the hip function and the residual displacement values in weight-bearing group (r(s) = -0.722, P = 0.001). But there was no correlation between the hip function and the residual displacement values in non weight-bearing group (r(s) = 0.481, P = 0.059). The results of clinical follow-up were similar to the correlation analysis results. In weight-bearing group, the hip function had strong negative correlation with step displacement (r(s) = 0.825, P = 0.002), but it had no correlation with gap displacement (r(s) = 0.577, P = 0.134). In patients with acetabular fracture, the hip function has correlation not only with the extent of the residual displacement but also with the location of the residual displacement, so the residual displacement of weight-bearing zone is a key factor to affect the hip function. In patients with residual displacement in weight-bearing zone, the bigger the step displacement is, the

Should money follow the patient: Financial implication for being the National Centre for the Treatment and Management of Pelvic and Acetabular Fractures in Ireland.

PubMed

Kelly, M E; Leonard, M; Green, C; Beggs, R; Cheung, C; McElwain, J; Morris, S

2013-12-01

Pelvic and acetabular fractures are complex injuries requiring specialist treatment. Our institution is the National Centre for Treatment and Management of these injuries. To audit all referrals to our institution over a 6-month period and calculate the cost incurred by being the national referral centre. Retrospective review of database, and subsequent allocation of Casemix points to assess total cost of treatment for each patient referred to our institution. 103 patients referred with pelvic or acetabular fracture for operative management. The furthest referral distance was 181miles. Over-all, the length of stay was 15.4 days. The average inclusive cost for a referral to our unit for operative management was €16,302. Pelvic and acetabular fractures are complex injuries that require specialist referral unit management. However for these units to remain sustainable money needs to "follow the patient". Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.

Effects of Titanium Mesh Surfaces-Coated with Hydroxyapatite/β-Tricalcium Phosphate Nanotubes on Acetabular Bone Defects in Rabbits

PubMed Central

Nguyen, Thuy-Duong Thi; Bae, Tae-Sung; Yang, Dae-hyeok; Park, Myung-sik; Yoon, Sun-jung

2017-01-01

The management of severe acetabular bone defects in revision reconstructive orthopedic surgery is challenging. In this study, cyclic precalcification (CP) treatment was used on both nanotube-surface Ti-mesh and a bone graft substitute for the acetabular defect model, and its effects were assessed in vitro and in vivo. Nanotube-Ti mesh coated with hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) was manufactured by an anodizing and a sintering method, respectively. An 8 mm diameter defect was created on each acetabulum of eight rabbits, then treated by grafting materials and covered by Ti meshes. At four and eight weeks, postoperatively, biopsies were performed for histomorphometric analyses. The newly-formed bone layers under cyclic precalcified anodized Ti (CP-AT) meshes were superior with regard to the mineralized area at both four and eight weeks, as compared with that under untreated Ti meshes. Active bone regeneration at 2–4 weeks was stronger than at 6–8 weeks, particularly with treated biphasic ceramic (p < 0.05). CP improved the bioactivity of Ti meshes and biphasic grafting materials. Moreover, the precalcified nanotubular Ti meshes could enhance early contact bone formation on the mesh and, therefore, may reduce the collapse of Ti meshes into the defect, increasing the sufficiency of acetabular reconstruction. Finally, cyclic precalcification did not affect bone regeneration by biphasic grafting materials in vivo. PMID:28686210

What Safe Zone? The Vast Majority of Dislocated THAs Are Within the Lewinnek Safe Zone for Acetabular Component Position.

PubMed

Abdel, Matthew P; von Roth, Philipp; Jennings, Matthew T; Hanssen, Arlen D; Pagnano, Mark W

2016-02-01

Numerous factors influence total hip arthroplasty (THA) stability including surgical approach and soft tissue tension, patient compliance, and component position. One long-held tenet regarding component position is that cup inclination and anteversion of 40° ± 10° and 15° ± 10°, respectively, represent a "safe zone" as defined by Lewinnek that minimizes dislocation after primary THA; however, it is clear that components positioned in this zone can and do dislocate. We sought to determine if these classic radiographic targets for cup inclination and anteversion accurately predicted a safe zone limiting dislocation in a contemporary THA practice. From a cohort of 9784 primary THAs performed between 2003 and 2012 at one institution, we retrospectively identified 206 THAs (2%) that subsequently dislocated. Radiographic parameters including inclination, anteversion, center of rotation, and limb length discrepancy were analyzed. Mean followup was 27 months (range, 0-133 months). The majority (58% [120 of 206]) of dislocated THAs had a socket within the Lewinnek safe zone. Mean cup inclination was 44° ± 8° with 84% within the safe zone for inclination. Mean anteversion was 15° ± 9° with 69% within the safe zone for anteversion. Sixty-five percent of dislocated THAs that were performed through a posterior approach had an acetabular component within the combined acetabular safe zones, whereas this was true for only 33% performed through an anterolateral approach. An acetabular component performed through a posterior approach was three times as likely to be within the combined acetabular safe zones (odds ratio [OR], 1.3; 95% confidence interval [CI], 1.1-1.6) than after an anterolateral approach (OR, 0.4; 95% CI, 0.2-0.7; p < 0.0001). In contrast, acetabular components performed through a posterior approach (OR, 1.6; 95% CI, 1.2-1.9) had an increased risk of dislocation compared with those performed through an anterolateral approach (OR, 0.8; 95% CI, 0.7-0.9; p

New proposal of mechanical reinforcement structures to annular REBaCuO bulk magnet for compact and cryogen-free NMR spectrometer

NASA Astrophysics Data System (ADS)

Fujishiro, H.; Takahashi, K.; Naito, T.; Yanagi, Y.; Itoh, Y.; Nakamura, T.

2018-07-01

We have proposed new reinforcement structures using an aluminum alloy ring to the annular REBaCuO bulks applicable to compact and cryogen-free 400 MHz (9.4 T) nuclear magnetic resonance (NMR) spectrometer using a numerical simulation of mechanical stress. The thermal compressive stress, σθcool, which was applied to the annular bulks during cooling due to the difference of thermal expansion coefficient between bulk and aluminum alloy, became fairly enhanced at the surface of the uppermost bulk for the new reinforcement structures, compared to the conventional reinforcement with the same height as the annular bulk, in which the compressive σθcool value was reduced. During field-cooled magnetization (FCM), the electromagnetic hoop stress, σθFCM, became the maximum at the innermost edge of the uppermost ring bulk at intermediate time step. The actual total hoop stress, σθ (= σθcool + σθFCM), due to both cooling and FCM processes was also analyzed and the new ring structures are fairly effective to reduce the σθ value and became lower than the fracture strength of the bulk. The new reinforcement structures have a possibility to avoid the fracture of the bulks and to realize a 400 MHz NMR spectrometer.

Electronic properties of superlattices on quantum rings.

PubMed

da Costa, D R; Chaves, A; Ferreira, W P; Farias, G A; Ferreira, R

2017-04-26

We present a theoretical study of the one-electron states of a semiconductor-made quantum ring (QR) containing a series of piecewise-constant wells and barriers distributed along the ring circumference. The single quantum well and the superlattice cases are considered in detail. We also investigate how such confining potentials affect the Aharonov-Bohm like oscillations of the energy spectrum and current in the presence of a magnetic field. The model is simple enough so as to allow obtaining various analytical or quasi-analytical results. We show that the well-in-a-ring structure presents enhanced localization features, as well as specific geometrical resonances in its above-barrier spectrum. We stress that the superlattice-in-a-ring structure allows giving a physical meaning to the often used but usually artificial Born-von-Karman periodic conditions, and discuss in detail the formation of energy minibands and minigaps for the circumferential motion, as well as several properties of the superlattice eigenstates in the presence of the magnetic field. We obtain that the Aharonov-Bohm oscillations of below-barrier miniband states are reinforced, owing to the important tunnel coupling between neighbour wells of the superlattice, which permits the electron to move in the ring. Additionally, we analysis a superlattice-like structure made of a regular distribution of ionized impurities placed around the QR, a system that may implement the superlattice in a ring idea. Finally, we consider several random disorder models, in order to study roughness disorder and to tackle the robustness of some results against deviations from the ideally nanostructured ring system.

Electronic properties of superlattices on quantum rings

NASA Astrophysics Data System (ADS)

da Costa, D. R.; Chaves, A.; Ferreira, W. P.; Farias, G. A.; Ferreira, R.

2017-04-01

We present a theoretical study of the one-electron states of a semiconductor-made quantum ring (QR) containing a series of piecewise-constant wells and barriers distributed along the ring circumference. The single quantum well and the superlattice cases are considered in detail. We also investigate how such confining potentials affect the Aharonov-Bohm like oscillations of the energy spectrum and current in the presence of a magnetic field. The model is simple enough so as to allow obtaining various analytical or quasi-analytical results. We show that the well-in-a-ring structure presents enhanced localization features, as well as specific geometrical resonances in its above-barrier spectrum. We stress that the superlattice-in-a-ring structure allows giving a physical meaning to the often used but usually artificial Born-von-Karman periodic conditions, and discuss in detail the formation of energy minibands and minigaps for the circumferential motion, as well as several properties of the superlattice eigenstates in the presence of the magnetic field. We obtain that the Aharonov-Bohm oscillations of below-barrier miniband states are reinforced, owing to the important tunnel coupling between neighbour wells of the superlattice, which permits the electron to move in the ring. Additionally, we analysis a superlattice-like structure made of a regular distribution of ionized impurities placed around the QR, a system that may implement the superlattice in a ring idea. Finally, we consider several random disorder models, in order to study roughness disorder and to tackle the robustness of some results against deviations from the ideally nanostructured ring system.

Basic considerations for determining the amount of press fit in acetabular cup endoprostheses as a function of the elastic bone behavior.

PubMed

Winter, Werner; Karl, Matthias

2014-10-01

Acetabular cup endoprostheses are frequently placed in pelvic bone, employing the mechanical principle of press fit. While a sufficiently stable bone-implant connection is desirable, deformation of the cup and fracture of the pelvis should be avoided. The goal of this work is to demonstrate the importance of the elastic properties of bone on the amount of press fit achievable in a specific situation. On the basis of previous work describing the relation between relative bone mineral density and relative elastic modulus for cortical and trabecular bone, mechanical equations were used for analyzing the press-fit loading situation of an acetabular cup. Additionally, a two-dimensional finite element model was used for visualizing the stress and strain situation in the host bone occurring as a consequence of implant insertion, as well as the effect of moment loads acting on the acetabular cup. Given the fact that oversizing the implant for a specific recipient site is the only clinical means of optimizing press fit, knowledge of the elastic properties of the host bone before implant selection would be beneficial. Such information could, for instance, be derived from intraoperative compressive testing of the host bone.

21 CFR 888.3320 - Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis. 888.3320 Section 888.3320 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic...

21 CFR 888.3320 - Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis. 888.3320 Section 888.3320 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic...

21 CFR 888.3320 - Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Hip joint metal/metal semi-constrained, with a cemented acetabular component, prosthesis. 888.3320 Section 888.3320 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic...

Hot piston ring/cylinder liner materials: Selection and evaluation

NASA Technical Reports Server (NTRS)

Sliney, Harold E.

1988-01-01

In current designs of the automotive (kinematic) Stirling engine, the piston rings are made of a reinforced polymer and are located below the pistons because they cannot withstand the high temperatures in the upper cylinder area. Theoretically, efficiency could be improved if hot piston rings were located near the top of the pistons. Described is a program to select piston ring and cylinder coating materials to test this theory. Candidate materials were screened, then subjected to a pin or disk friction and wear test machine. Tests were performed in hydrogen at specimen temperatures up to 760 C to simulate environmental conditions in the region of the hot piston ring reversal. Based on the results of these tests, a cobalt based alloy, Stellite 6B, was chosen for the piston rings and PS200, which consists of a metal-bonded chromium carbide matrix with dispersed solid lubricants, was chosen as the cylinder coating. Tests of a modified engine and a baseline engine showed that the hot ring reduced specific fuel consumption by up to 7 percent for some operating conditions and averaged about 3 percent for all conditions evaluated. Related applications of high-temperature coatings for shaft seals and as back-up lubricants are also described.

Biocompatibility of Bespoke 3D-Printed Titanium Alloy Plates for Treating Acetabular Fractures

PubMed Central

Xiao, Xingling; Wang, Yimeng; Gu, Cheng; Wang, Canbin; Chen, Jiahui; Liu, Han; Luo, Juan; Li, Tao

2018-01-01

Treatment of acetabular fractures is challenging, not only because of its complicated anatomy but also because of the lack of fitting plates. Personalized titanium alloy plates can be fabricated by selective laser melting (SLM) but the biocompatibility of these three-dimensional printing (3D-printed) plates remains unknown. Plates were manufactured by SLM and their cytocompatibility was assessed by observing the metabolism of L929 fibroblasts incubated with culture medium extracts using a CCK-8 assay and their morphology by light microscopy. Allergenicity was tested using a guinea pig maximization test. In addition, acute systemic toxicity of the 3D-printed plates was determined by injecting extracts from the implants into the tail veins of mice. Finally, the histocompatibility of the plates was investigated by implanting them into the dorsal muscles of rabbits. The in vitro results suggested that cytocompatibility of the 3D-printed plates was similar to that of conventional plates. The in vivo data also demonstrated histocompatibility that was comparable between the two manufacturing techniques. In conclusion, both in vivo and in vitro experiments suggested favorable biocompatibility of 3D-printed titanium alloy plates, indicating that it is a promising option for treatment of acetabular fractures. PMID:29682523

Is transverse acetabular ligament an anatomical landmark to reliably orient the cup in primary total hip arthroplasty?

PubMed

Viste, A; Chouteau, J; Testa, R; Chèze, L; Fessy, M-H; Moyen, B

2011-05-01

Accurate positioning of the acetabular cup in primary total hip arthroplasty is critical to decrease the rate of dislocation. Inaccurate orientation of the cup is the most common error during this procedure. Target acetabular orientation is still controversial. An original study found a dislocation rate of 0.6% when the cup was aligned with the transverse acetabular ligament (TAL). TAL is a patient-specific anatomical landmark and a tool for cup orientation. Eight cadaveric pelves (14 hips included for study) were harvested in toto at our research laboratory. Anatomical versions of the TAL, labrum and horns were measured in relation to the anterior pelvic plane. A navigator sensor and an optoelectronic device (Motion Analysis™) were used. Anatomical versions of the TAL, horns and labrum averaged 1.9° (range, -8° to +13.3°), 3° (range, -12.2° to 14°), and 26.3° (range, 17.4° to 41.8°), respectively. To our knowledge, this is the first study to report the orientation of the periacetabular soft-tissues. TAL anteversion was outside the safe zone described by Lewinnek, while labrum anteversion was within this safe-zone. We discuss the reference used, Lewinnek's safe zone, and functional orientation of the implants. Lewinnek's safe-zone does not seem to be valid. The TAL seems to be a specific reference for each patient but its reliability must still be confirmed as an adequate reference for positioning the cup in total hip arthroplasty. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

Does using a polyethylene RM press-fit cup modify the preparation of the acetabulum and acetabular offset in primary hip arthroplasty?

PubMed

Erivan, R; Aubret, S; Villatte, G; Mulliez, A; Descamps, S; Boisgard, S

2017-09-01

When performing total hip arthroplasty (THA), it is important to maintain the femoral and acetabular offsets to ensure good joint stability and to restore the function of the hip abductor muscles. In our practice, we mainly use a lateralized stem and hollow out the acetabulum to the quadrilateral plate to accommodate a press-fit polyethylene cup. However, the repercussions of this preparation method, which is driven by the cup's design, are not known. We carried out a retrospective study to assess: (1) the changes in the femoral and acetabular offset; (2) the height of the center of rotation; and (3) the repercussions on wear. We hypothesized there would be no significant differences between the preoperative and postoperative femoral and acetabular offsets. We reviewed 88 primary THA cases performed with the RM Pressfit™ cup that had a minimum of 5 years' follow-up. A lateralized self-locking Muller-type cemented femoral stem was used in 92.0% of cases and a standard stem in 8.0%. Measurements were done on plain radiographs with MHP™ and Mesurim Pro™ software. The average follow-up was 6.5 years (5-8). On average, the acetabular offset was reduced by 2.75mm±5.9 mm (range: -17.5 to +10.6 mm) (P<0.001) and the femoral offset was increased by 0.01mm±5.5 mm (range: -17.8 to +11.0 mm) (P=0.99). In terms of total offset, medialization of 2.74mm±7 mm (range: -17.7 to +18.2mm) was found (P=0.001). The acetabular center of rotation was on average 4.77mm±5.1 mm higher (P<0.001). The mean annual wear at the more recent follow-up (min.: 5 years) was 0.068mm (range: 0.01 to 0.25mm) per year. The wear was not impacted by having more than 5mm change in offset. Measurements of acetabular offset revealed statistically significant medialization due to the type of implant used and the surgical technique. The anatomical technique consists of positioning the cup in subchondral bone without contacting the quadrilateral plate. This preserves bone stock, which may be

A hierarchy of computationally derived surgical and patient influences on metal on metal press-fit acetabular cup failure.

PubMed

Clarke, S G; Phillips, A T M; Bull, A M J; Cobb, J P

2012-06-01

The impact of anatomical variation and surgical error on excessive wear and loosening of the acetabular component of large diameter metal-on-metal hip arthroplasties was measured using a multi-factorial analysis through 112 different simulations. Each surgical scenario was subject to eight different daily loading activities using finite element analysis. Excessive wear appears to be predominantly dependent on cup orientation, with inclination error having a higher influence than version error, according to the study findings. Acetabular cup loosening, as inferred from initial implant stability, appears to depend predominantly on factors concerning the area of cup-bone contact, specifically the level of cup seating achieved and the individual patient's anatomy. The extent of press fit obtained at time of surgery did not appear to influence either mechanism of failure in this study. Copyright © 2012 Elsevier Ltd. All rights reserved.

Press-fit versus threaded acetabular cups in total hip arthroplasty: Functional and radiological results after five years.

PubMed

Ellenrieder, Martin; Bader, Rainer; Bergschmidt, Philipp; Mittelmeier, Wolfram

2016-03-01

Prospectively the outcome after total hip replacement with a new threaded acetabular cup design was compared to an established press-fit cup. After 1, 2 and 5 years, the 36-item Short Form Health Survey, Western Ontario and McMaster University Osteoarthritis Index and Harris Hip Score revealed no significant differences between the two groups (each group: n=42 patients), except for a higher Harris Hip Score in the threaded cup group after five years (p=0.02). After five years, one threaded cup had a mild radiolucent line without further signs of loosening. All other cups of both groups (98.6%) showed a full osseous integration. The cup inclination angle ranged from 41-58° (threaded cups) to 39-77° (press-fit cups). The new threaded cup provides equivalent clinical outcomes and osseous integration but more precise implant positioning compared to the press-fit design. No complications typically ascribed to threaded cups (acetabular fractures, bone resorption, nerve impairment) occurred.

Relationship Between the Lateral Center-Edge Angle and 3-Dimensional Acetabular Coverage.

PubMed

Wylie, James D; Kapron, Ashley L; Peters, Christopher L; Aoki, Stephen K; Maak, Travis G

2017-04-01

The lateral center-edge angle (LCEA) is an important measurement in understanding acetabular morphology and has had multiple interpretations. Misunderstanding of the LCEA and its relationship with acetabular 3-dimensional (3D) morphology may result in misdiagnosis and poor outcomes. To determine the discrepancy between bone-edge and sourcil-edge LCEA measurements on anteroposterior (AP) radiographs and to determine the 3D anatomic location of the sourcil-edge and bone-edge LCEA measurements. Cohort study (diagnosis); Level of evidence, 2. The LCEA was measured on radiographs to both the sourcil-edge and bone-edge on AP images of 60 symptomatic hips. On computed tomography (CT), coronal slices producing an LCEA matching the magnitude of each AP LCEA were identified. These coronal slices were mapped to a sagittal image of the acetabulum, which was divided into a standard clockface (3 = anterior, 12 = superior). We identified clockface locations corresponding to the AP sourcil-edge and bone-edge LCEA measurements. Paired t tests identified differences in magnitude and location of the bone and sourcil LCEAs. Limits of agreement were calculated for the differences between measures. Intraclass correlation coefficients (ICCs) assessed inter- and intraobserver repeatability. On the AP radiographs, the bone-edge LCEA was a mean 4.7° (95% CI, -4.0° to 13.3°) greater than the sourcil-edge LCEA ( P < .001). On CT, the sagittal clockface location of the sourcil-edge LCEA was more anterior compared with the sagittal clockface location of the maximum bone-edge LCEA (1:03 ± 0:42 vs 12:06 ± 0:30, respectively; P < .001). In hips with a difference >5° between sourcil-edge and bone-edge measurements, the coronal CT slice corresponding to the sourcil-edge LCEA was significantly more anterior (1:26 ± 0:35) than the CT slice corresponding to the bone-edge LCEA (11:46 ± 0:29; P < .001). This significant difference was similar in location but less pronounced in hips with a

Atypical anterior wall fracture of the acetabulum: case series of anterior acetabular rim fracture without involvement of the pelvic brim.

PubMed

Lenarz, Christopher J; Moed, Berton R

2007-09-01

The purpose of this study was to describe a form of anterior wall acetabular fracture, which has been inadequately defined in the literature. Retrospective analysis of consecutive patients. Level 1 trauma center. A retrospective analysis of consecutive acetabulum patients treated by a single surgeon between 1999 and 2005 identified 6 patients with a form of anterior wall fracture without involvement of the pelvic brim. All fractures were treated operatively. Open reduction and internal fixation through an anterior surgical approach. Final radiographic appearance and modified Merle d'Aubigne score. All 6 cases demonstrated characteristics of an atypical fracture of the anterior wall, involving the anterior rim of the acetabulum similar in nature to those described for the posterior wall, rather than the standard anterior wall fracture type described by Letournel. Of the 6 cases that were identified, 5 had follow-up 1 year or greater with a mean modified Merle d'Aubigne Score of 17 (range: 17-18). A form of anterior wall acetabular fracture exists, which involves the anterior acetabular rim without involvement of the pelvic brim. It can occur in young patients with high-energy mechanisms of injury, as well as in the elderly with low-energy trauma. With appropriate surgical management, using a modified Smith-Peterson approach, good to excellent clinical outcomes should be expected.

Inter- and intra-observer variability of radiography and computed tomography for evaluation of Zurich cementless acetabular cup placement ex vivo.

PubMed

Leasure, Jessica O; Peck, Jeffrey N; Villamil, Armando; Fiore, Kara L; Tano, Cheryl A

2016-11-23

To evaluate the inter- and intra-observer variability in measurement of the angle of lateral opening (ALO) and version angle measurement using digital radiography and computed tomography (CT). Each hemipelvis was implanted with a cementless acetabular cup. Ventrodorsal and mediolateral radiographs were made of each pelvis, followed by CT imaging. After removal of the first cup, the pelves were implanted with an acetabular cup in the contralateral acetabulum and imaging was repeated. Three surgeons measured the ALO and version angles three times for each cup from the mediolateral radiographic projection. The same measurements were made using three-dimensional multiplanar reconstructions from CT images. Two anatomical axes were used to measure pelvic inclination in the sagittal plane, resulting in six measurements per cup. Two-way repeated measures analysis of variance evaluated inter- and intra-observer repeatability for radiographic and CT-based measurements. Version angle based on radiographic measurement did not differ within surgeons (p = 0.433), but differed between surgeons (p <0.001). Radiographic measurement of ALO differed within surgeons (p = 0.006) but not between surgeons (p = 0.989). The ALO and version angle measured on CT images did not differ with or between surgeons. Assessment of inter- and intra-observer measurement of ALO and version angle was more reproducible using CT images than conventional mediolateral radiography for a Zurich cementless acetabular cup.

Initial stability of cementless acetabular cups: press-fit and screw fixation interaction--an in vitro biomechanical study.

PubMed

Tabata, Tomonori; Kaku, Nobuhiro; Hara, Katsutoshi; Tsumura, Hiroshi

2015-04-01

Press-fit and screw fixation are important technical factors to achieve initial stability of a cementless acetabular cup for good clinical results of total hip arthroplasty. However, how these factors affect one another in initial cup fixation remains unclear. Therefore, this study aimed to evaluate the mutual influence between press-fit and screw fixation on initial cup stability. Foam bone was subjected to exact hemispherical-shape machining to diameters of 48, 48.5 and 49 mm. A compressive force was applied to ensure seating of a 48-mm-diameter acetabular cup in the foam bone prior to testing. Screws were inserted in six different conditions and tightened in a radial direction at the same torque strength. Then, the socket was rotated with a twist-testing machine, and the torque value at the start of axial rotation between the socket and the foam bone was measured under each screw condition. The torque values for the 48-mm-diameter reaming were >20 N m higher than those for the 48.5- and 49-mm-diameter reaming in each screw condition, indicating that press-fit fixation is stronger than screw fixation. Meanwhile, torque values for the 48.5- and 49-mm-diameter reaming tended to increase with increasing the number of screws. According to our experiment, press-fit fixation of a cementless acetabular cup achieved rigid stability. Although the supplemental screws increased stability of the implant under good press-fit conditions, they showed little impact on whole-cup stability. In the case of insufficient press-fit fixation, cup stability depends on screw stability and increasing the number of additional screws increases cup stability.

The effect of bearing friction torques on the primary stability of press-fit acetabular cups: A novel in vitro method.

PubMed

Alexander, Jahnke; Stefan, Schroeder; Alfonso, Fonseca Ulloa Carlos; Adam, Ahmed Gafar; Alexander, Ishaque Bernd; Markus, Rickert

2018-05-10

Aseptic loosening is the main reason for revision of total hip arthroplasty, and relative micromotions between cementless acetabular cups and bone play an important role regarding their comparatively high loosening rate. Therefore, the aim of the present study was to analyze the influence of resulting frictional torques on the primary stability of press-fit acetabular cups subjected to two different bearing partners. A cementless press-fit cup was implanted in bone-like foam. Primary stability of the cup was analyzed by determining spatial total, translational and rotational interface micromotions by means of an eddy current sensor measuring system. Torque transmission into the cup was realized by three synchronous servomotors considering resultant friction torques based on constant friction for ceramic-on-ceramic (CoC: µ = 0.044; max. resultant torque: 1.5 Nm) and for ceramic-on-polyethylene (CoP: µ = 0.063; max. resultant torque: 1.9 Nm) bearing partners. Rotational micromotion of CoC was 8.99 ± 0.85µm and of CoP 13.39 ± 1.43µm. Translational micromotion of CoC was 29.93 ± 1.44µm and of CoP 39.91 ± 2.25µm. Maximum total relative micromotions were 37.10 ± 1.07µm for CoC and 51.64 ± 2.18µm for CoP. Micromotions resulting from CoC were statistically lower than those resulting from CoP (p < 0.05). The described 3D-measuring set-up offers a novel in vitro method of measuring primary stability of acetabular cups. We can therefore conclude, that primary stability of acetabular cup systems can be observed using either the lower friction curve (CoC) or the higher friction curve (CoP). In future studies different cup designs or cup fixation mechanisms may be tested and compared in vitro and assessed prior to implantation. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Secure Screw Placement in Management of Acetabular Fractures Using the Suprapectineal Quadrilateral Buttress Plate.

PubMed

Egli, R J; Keel, M J B; Cullmann, J L; Bastian, J D

2017-01-01

Acetabular fractures involving predominantly the anterior column associated with a disruption of the quadrilateral surface can be treated with instrumentation implementing the stabilization of the quadrilateral surface. The recently introduced suprapectineal quadrilateral buttress plate is specifically designed to prevent secondary medial subluxation of the femoral head, especially in elderly patients with reduced ability for partial weight bearing. Whereas there are guidelines available for safe screw fixation for the anterior and posterior columns, there might be a concern for intra-articular placement of screws placed through the infrapectineal part of the quadrilateral buttress plate. Within this report we analyzed retrospectively screw placement in 30 plates in postoperative CT scans using algorithms for metal artifact reduction. None of the screws of the buttress plate penetrated the hip joint. We describe the placement, length, and spatial orientation of the screws used for fracture fixation and suggest that the use of intraoperative image intensifiers with a combined inlet-obturator view of 30-45° best projects the screws and the hip joint. Preoperative knowledge of approximate screw placement and information for accurate intraoperative imaging may contribute to safe acetabular fracture fixation and may reduce operating time and limit radiation exposure to the patient and the personnel. This trial is registered with KEK-BE: 266/2014.

Initial stability of a highly porous titanium cup in an acetabular bone defect model.

PubMed

Yoshimoto, Kensei; Nakashima, Yasuharu; Wakiyama, Miyo; Hara, Daisuke; Nakamura, Akihiro; Iwamoto, Mikio

2018-04-12

The purpose of this study was to quantify the initial stability of a highly porous titanium cup using an acetabular bone defect model. The maximum torque of a highly porous titanium cup, with a pore size of 640 μm and porosity of 60%, was measured using rotational and lever-out torque testing and compared to that of a titanium-sprayed cup. The bone models were prepared using a polyurethane foam block and had three levels of bone coverage: 100, 70, and 50%. The highly porous titanium cup demonstrated significantly higher maximum torque than the titanium-sprayed cups in the three levels of bone defects. On rotational torque testing, it was found to be 1.5, 1.3, and 1.3 times stronger than the titanium-sprayed cups with 100, 70 and 50% bone coverage, respectively. Furthermore, it was found to be 2.2, 2.3, and 1.5 times stronger on lever-out testing than the titanium-sprayed cup. No breakage in the porous layers was noted during the testing. This study provides additional evidence of the initial stability of highly porous titanium cup, even in the presence of acetabular bone defects. Copyright © 2018. Published by Elsevier B.V.

[Biomechanical significance of the acetabular roof and its reaction to mechanical injury].

PubMed

Domazet, N; Starović, D; Nedeljković, R

1999-01-01

The introduction of morphometry into the quantitative analysis of the bone system and functional adaptation of acetabulum to mechanical damages and injuries enabled a relatively simple and acceptable examination of morphological acetabular changes in patients with damaged hip joints. Measurements of the depth and form of acetabulum can be done by radiological methods, computerized tomography and ultrasound (1-9). The aim of the study was to obtain data on the behaviour of acetabular roof, the so-called "eyebrow", by morphometric analyses during different mechanical injuries. Clinical studies of the effect of different loads on acetabular roof were carried out in 741 patients. Radiographic findings of 400 men and 341 women were analysed. The control group was composed of 148 patients with normal hip joints. Average age of the patients was 54.7 years and that of control subjects 52.0 years. Data processing was done for all examined patients. On the basis of our measurements the average size of female "eyebrow" ranged from 24.8 mm to 31.5 mm with standard deviation of 0.93 and in men from 29.4 mm to 40.3 mm with standard deviation of 1.54. The average size in the whole population was 32.1 mm with standard deviation of 15.61. Statistical analyses revealed high correlation coefficients between the age and "eyebrow" size in men (r = 0.124; p < 0.05); it was statically in inverse proportion (Graph 1). However, in female patients the correlation coefficient was statistically significant (r = 0.060; p > 0.05). The examination of the size of collodiaphysial angle and length of "eyebrow" revealed that "eyebrow" length was in inverse proportion to the size of collodiaphysial angle (r = 0.113; p < 0.05). The average "eyebrow" length in relation to the size of collodiaphysial angle ranged from 21.3 mm to 35.2 mm with standard deviation of 1.60. There was no statistically significant correlation between the "eyebrow" size and Wiberg's angle in male (r = 0.049; p > 0.05) and

Bearing Capacity Tests on Ice Reinforced With Geogrid

DTIC Science & Technology

1992-12-01

reinforce an ice bridge on rivers, lakes and oceans every winter in cold re- the Imjin River in Korea; Carnes (1964) reports that gions around the...increased the flexural aircraft in World War U. Although this "Pykrete," strength up to 31%. Creep tests on ice beams with as it was called, never was used...The Second World War , Clos- CONCLUSIONS ing the Ring, vol. 5. Boston: Houghton Mifflin, pp. 75-76. Thebearingcapacity testsconductedinCRREL’s

Is metal-on-metal squeaking related to acetabular angle of inclination?

PubMed

Bernasek, Thomas; Fisher, David; Dalury, David; Levering, Melissa; Dimitris, Kirk

2011-09-01

Postoperative audible squeaking has been well documented in ceramic-on-ceramic hip prostheses, and several metal-on-metal (MOM) THA designs, specifically those used for large-head resurfacing and MOM polyethylene sandwich designs, and are attributed to different implant- and patient-specific factors. Current literature does not identify the incidence of squeaking in modular MOM THA or possible etiologic factors. Our purposes were to (1) identify the incidence of squeaking in modular MOM prostheses in THA; (2) determine whether males or females were more likely to have squeaking; and (3) determine whether the incidence of squeaking relates to acetabular inclination angle. We retrospectively reviewed the patient records and radiographs of 539 patients (542 hips) from three independent centers who underwent a MOM THA between February 2001 and December 2005. Demographic and implant factors were evaluated, including measurement of cup inclination angles. The minimum followup was 36 months (mean, 76 months; range, 36-119 months). We identified squeaking in eight of the 542 hips (1.5%); five were in women and two were in men (one patient had bilateral squeaking). The time to onset of patient-reported audible squeaking averaged 23 months (range, 6-84 months). Squeaking was more likely to occur in women (six of eight hips). No hips with 45º or less acetabular inclination squeaked (291 hips); eight of 251 hips (3.2%) with inclination angles greater than 45º squeaked. Patients who reported squeaking had higher inclination angles than those who did not report squeaking. Our observations suggest an increased frequency of squeaking in female patients and in patients with greater inclination angles with this MOM implant design.

A pilot trial comparing the tear-out behavior in screw-sockets and cemented polyethylene acetabular components - a cadaveric study.

PubMed

Möbius, R; Schleifenbaum, S; Grunert, R; Löffler, S; Werner, M; Prietzel, T; Hammer, N

2016-10-01

The removal of well-fixed acetabular components following THA (total hip arthroplasty) is a difficult operation and could be accompanied by the loss of acetabular bone stock. The optimal method for fixation is still under debate. The aim of this pilot study was to compare the tear-out resistance and failure behavior between osseo-integrated and non-integrated screw cups. Furthermore, we examined whether there are differences in the properties mentioned between screw sockets and cemented polyethylene cups. Tear-out resistance and related mechanical work required for the tear-out of osseo-integrated screw sockets are higher than in non-integrated screw sockets. Ten human coxal bones from six cadavers with osseo-integrated screw sockets (n=4), non-integrated (implanted post-mortem, n=3) screw sockets and cemented polyethylene cups (n=3) were used for tear-out testing. The parameters axial failure load and mechanical work for tear-out were introduced as measures for determining the stability of acetabular components following THA. The osseo-integrated screw sockets yielded slightly higher tear-out resistance (1.61±0.26kN) and related mechanical work compared to the non-integrated screw sockets (1.23±0.39kN, P=0.4). The cemented polyethylene cups yielded the lowest tear-out resistance with a failure load of 1.18±0.24kN. Compared to the screw cups implanted while alive, they also differ on a non-significant level (P=0.1). Osseous failure patterns differed especially for the screw sockets compared to the cemented polyethylene cups. Osseo-integration did not greatly influence the tear-out stability in cementless screw sockets following axial loading. Furthermore, the strength of the bone-implant-interface of cementless screw sockets appears to be similar to cemented polyethylene cups. However, given the high failure load, high mechanical load and because of the related bone failure patterns, removal should not be performed by means of tear-out but rather by osteotomes

Acetabular cup position and risk of dislocation in primary total hip arthroplasty.

PubMed

Seagrave, Kurt G; Troelsen, Anders; Malchau, Henrik; Husted, Henrik; Gromov, Kirill

2017-02-01

Background and purpose - Hip dislocation is one of the most common complications following total hip arthroplasty (THA). Several factors that affect dislocation have been identified, including acetabular cup positioning. Optimal values for cup inclination and anteversion are debatable. We performed a systematic review to describe the different methods for measuring cup placement, target zones for cup positioning, and the association between cup positioning and dislocation following primary THA. Methods - A systematic search of literature in the PubMed database was performed (January and February 2016) to identify articles that compared acetabular cup positioning and the risk of dislocation. Surgical approach and methods for measurement of cup angles were also considered. Results - 28 articles were determined to be relevant to our research question. Some articles demonstrated that cup positioning influenced postoperative dislocation whereas others did not. The majority of articles could not identify a statistically significant difference between dislocating and non-dislocating THA with regard to mean angles of cup anteversion and inclination. Most of the articles that assessed cup placement within the Lewinnek safe zone did not show a statistically significant reduction in dislocation rate. Alternative target ranges have been proposed by several authors. Interpretation - The Lewinnek safe zone could not be justified. It is difficult to draw broad conclusions regarding a definitive target zone for cup positioning in THA, due to variability between studies and the likely multifactorial nature of THA dislocation. Future studies comparing cup positioning and dislocation rate should investigate surgical approach separately. Standardized tools for measurement of cup positioning should be implemented to allow comparison between studies.

Computed tomography arthrography with traction in the human hip for three-dimensional reconstruction of cartilage and the acetabular labrum

PubMed Central

Henak, C.R.; Abraham, C.L.; Peters, C.L.; Sanders, R.K.; Weiss, J.A.; Anderson, A.E.

2014-01-01

AIM To develop and demonstrate the efficacy of a computed tomography arthrography (CTA) protocol for the hip that enables accurate three-dimensional reconstructions of cartilage and excellent visualization of the acetabular labrum. MATERIALS AND METHODS Ninety-three subjects were imaged (104 scans); 68 subjects with abnormal anatomy, 11 patients after periacetabular osteotomy surgery, and 25 subjects with normal anatomy. Fifteen to 25 ml of contrast agent diluted with lidocaine was injected using a lateral oblique approach. A Hare traction splint applied traction during CT. The association between traction force and intra-articular joint space was assessed qualitatively under fluoroscopy. Cartilage geometry was reconstructed from the CTA images for 30 subjects; the maximum joint space under traction was measured. RESULTS Using the Hare traction splint, the intra-articular space and boundaries of cartilage could be clearly delineated throughout the joint; the acetabular labrum was also visible. Dysplastic hips required less traction (~5 kg) than normal and retroverted hips required (>10 kg) to separate the cartilage. An increase in traction force produced a corresponding widening of the intra-articular joint space. Under traction, the maximum width of the intra-articular joint space during CT ranged from 0.98–6.7 mm (2.46 ± 1.16 mm). CONCLUSIONS When applied to subjects with normal and abnormal hip anatomy, the CTA protocol presented yields clear delineation of the cartilage and the acetabular labrum. Use of a Hare traction splint provides a simple, cost-effective method to widen the intra-articular joint space during CT, and provides flexibility to vary the traction as required. PMID:25070373

A new technique for radiographic measurement of acetabular cup orientation.

PubMed

Derbyshire, Brian; Diggle, Peter J; Ingham, Christopher J; Macnair, Rory; Wimhurst, James; Jones, Henry Wynn

2014-02-01

Accurate radiographic measurement of acetabular cup orientation is required in order to assess susceptibility to impingement, dislocation, and edge loading wear. In this study, the accuracy and precision of a new radiographic cup orientation measurement system were assessed and compared to those of two commercially available systems. Two types of resurfacing hip prostheses and an uncemented prosthesis were assessed. Radiographic images of each prosthesis were created with the cup set at different, known angles of version and inclination in a measurement jig. The new system was the most accurate and precise and could repeatedly measure version and inclination to within a fraction of a degree. In addition it has a facility to distinguish cup retroversion from anteversion on anteroposterior radiographs. © 2013.

Radiographic Measurement of Displacement in Acetabular Fractures: A Systematic Review of the Literature.

PubMed

Dodd, Andrew; Osterhoff, Georg; Guy, Pierre; Lefaivre, Kelly A

2016-06-01

To report methods of measurement of radiographic displacement and radiographic outcomes in acetabular fractures described in the literature. A systematic review of the English literature was performed using EMBASE and Medline in August 2014. Inclusion criteria were studies of operatively treated acetabular fractures in adults with acute (<6 weeks) open reduction and internal fixation that reported radiographic outcomes. Exclusion criteria included case series with <10 patients, fractures managed >6 weeks from injury, acute total hip arthroplasty, periprosthetic fractures, time frame of radiographic outcomes not stated, missing radiographic outcome data, and non-English language articles. Basic information collected included journal, author, year published, number of fractures, and fracture types. Specific data collected included radiographic outcome data, method of measuring radiographic displacement, and methods of interpreting or categorizing radiographic outcomes. The number of reproducible radiographic measurement techniques (2/64) and previously described radiographic interpretation methods (4) were recorded. One radiographic reduction grading criterion (Matta) was used nearly universally in articles that used previously described criteria. Overall, 70% of articles using this criteria documented anatomic reductions. The current standard of measuring radiographic displacement in publications dealing with acetabulum fractures almost universally lacks basic description, making further scientific rigor, such as testing reproducibility, impossible. Further work is necessary to standardize radiographic measurement techniques, test their reproducibility, and qualify their validity or determine which measurements are important to clinical outcomes. Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Wear versus Thickness and Other Features of 5-Mrad Crosslinked UHMWPE Acetabular Liners

PubMed Central

Shen, Fu-Wen; Lu, Zhen

2010-01-01

Background The low wear rates of crosslinked polyethylenes provide the potential to use larger diameters to resist dislocation. However, this requires the use of thinner liners in the acetabular component, with concern that higher contact stresses will increase wear, offsetting the benefits of the crosslinking. Questions/purposes We asked the following questions: Is the wear of conventional and crosslinked polyethylene liners affected by ball diameter, rigidity of backing, and liner thickness? Are the stresses in the liner affected by thickness? Methods Wear rates were measured in a hip simulator and stresses were calculated using finite element modeling. Results Without crosslinking, the wear rate was 4% to 10% greater with a 36-mm diameter than a 28-mm diameter. With crosslinking, wear was 9% lower with a 36-mm diameter without metal backing and 4% greater with metal backing. Reducing the thickness from 6 mm to 3 mm increased the contact stress by 46%, but the wear rate decreased by 19%. Conclusions The reduction in wear with 5 Mrad of crosslinking was not offset by increasing the diameter from 28 mm to 36 mm or by using a liner as thin as 3 mm. Clinical Relevance The results indicate, for a properly positioned 5-Mrad crosslinked acetabular component and within the range of dimensions evaluated, neither wear nor stresses in the polyethylene are limiting factors in the use of larger-diameter, thinner cups to resist dislocation. PMID:20848244

Long-term results of uncemented alumina acetabular implants.

PubMed

Boehler, M; Knahr, K; Plenk, H; Walter, A; Salzer, M; Schreiber, V

1994-01-01

We report the clinical and tribological performance of 67 ceramic acetabular prostheses implanted between 1976 and 1979 without bone cement. They articulated with ceramic femoral heads mounted on mental femoral stems. After a mean elapsed period of 144 months, 59 sockets were radiographically stable but two showed early signs and six showed late signs of loosening. Four of the loose sockets have been revised. Histological analysis of the retrieved tissue showed a fibrous membrane around all the implants, with fibrocartilage in some. There was no bone ingrowth, and the fibrous membrane was up to 6 mm thick and infiltrated with lymphocytes, plasma cells, and macrophages. Intra- and extracellular birefringent wear particles were seen. Tribological analysis showed total wear rates in two retrieved alumina-on-alumina joints of 2.6 microns per year in a stable implant and 68 microns in a loose implant. Survival analysis showed a revision rate of 12.4% at 136 months.

Migration characteristics and early clinical results of a novel-finned press-fit acetabular cup.

PubMed

Kaipel, Martin; Prenner, Anton; Bachl, Sebastian; Farr, Sebastian; Sinz, Günter

2014-04-01

Ana Nova® is a novel-finned press-fit acetabular cup which showed superior biomechanical characteristics in an experimental set-up. Using Einzel Bild Röntgen Analyse (EBRA) measurements should offer the opportunity to predict implant survival at an early stage. The purpose of this study was to assess migration and clinical outcome 2 years after total hip replacement by a novel-finned press-fit acetabular cup. In this study, migration and clinical results of the implant were prospectively assessed in 67 patients. Clinical outcome was assessed using the Harris hip score (HHS). Migration analyses were performed using the computer assisted EBRA system. Data were analyzed for normal distribution using the Kolmogorov-Smirnov test. Group comparisons were performed using the analysis of variance (ANOVA) test. P-values less than 0.05 were considered statistically significant. At 2 years after surgery, none of the implants needed revision and HHS increased from 39.7 up to 92.2. In contrast to the beneficial clinical outcome, 17 of 44 patients showed increased total migration ( 1 mm/2a). Adverse migration data in this study might predict aseptic loosening and decreased survival of the implant. According to previous studies, it is possible that this effect occurred because of limited accuracy of the EBRA system. In our opinion, migration analyses may not be recommended as a screening tool in a 2 year follow-up.

How often does open reduction and internal fixation of geriatric acetabular fractures lead to hip arthroplasty?

PubMed

O'Toole, Robert V; Hui, Emily; Chandra, Amit; Nascone, Jason W

2014-03-01

We hypothesized that open reduction and internal fixation (ORIF) of displaced acetabular fractures in geriatric patients result in a low rate of conversion to hip arthroplasty and satisfactory hip-specific validated outcome scores at medium-term follow-up. Retrospective review. Level I trauma center. One hundred forty-seven consecutive patients who were 60 years or older who had acetabular fractures were treated at our center from 2001 through 2006. During this time period, fractures meeting operative criteria were treated with ORIF unless medical conditions warranted nonoperative treatment. Twenty-nine patients were lost to follow-up, 46 were deceased, and 11 declined to participate, leaving 61 potential patients for inclusion, 46 of whom were treated with ORIF (average follow-up, 4.4 years; range, 1.1-8.0 years). Standardized telephone interviews included hip-specific questions and validated outcome measures. Rates of conversion to hip arthroplasty and hip-specific validated outcome scores. Among 46 patients treated with ORIF (15 others were treated nonoperatively or with percutaneous screw fixation), 28% underwent hip arthroplasty an average 2.5 years after injury (range, 0.4-5.5 years) and had an average Western Ontario and McMaster Universities Index of Osteoarthritis score of 17 (range, 0-56; n = 38). This score is similar to or better than the typical scores after elective arthroplasty for arthritis and much better than the scores for patients with established arthritis (P < 0.05). The average SF-8 Health Survey physical component score was 46.1 (range, 31-62), similar to US population norms for the geriatric age group (P > 0.20). Few data exist regarding the treatment outcomes for geriatric acetabular fractures. It is difficult for clinicians to decide among ORIF, percutaneous fixation, acute arthroplasty, and nonoperative treatment. Our protocol of mostly ORIF showed a high 1-year mortality rate of 25% and a rate of conversion to arthroplasty after ORIF of

Restoration of the centre of rotation in primary total hip arthroplasty: the influence of acetabular floor depth and reaming technique.

PubMed

Meermans, G; Doorn, J Van; Kats, J-J

2016-12-01

One goal of total hip arthroplasty is to restore normal hip anatomy. The aim of this study was to compare displacement of the centre of rotation (COR) using a standard reaming technique with a technique in which the acetabulum was reamed immediately peripherally and referenced off the rim. In the first cohort the acetabulum was reamed to the floor followed by sequentially larger reamers. In the second cohort the acetabulum was only reamed peripherally, starting with a reamer the same size as the native femoral head. Anteroposterior pelvic radiographs were analysed for acetabular floor depth and vertical and horizontal position of the COR. Horizontally, the mean medial displacement of the COR was 0.8 mm (standard deviation (sd) 1.4) in the peripheral remaing group and 5.0 mm (sd 3.30) in the standard reaming group (p < 0.001). Vertically, the mean superior displacement of the COR was 0.7 mm (sd 1.3) in the peripheral reaming group and 3.7 mm (sd 2.6) in the standard reaming group (p < 0.001). In the standard reaming group, there was a strong correlation between the pre-operative acetabular floor depth and displacement of the COR (p < 0.001). Reaming the acetabulum to the floor can lead to significant displacement of the COR medially and superiorly. This displacement is related to the pre-operative acetabular floor depth and cannot always be compensated by using a high offset stem. Cite this article: Bone Joint J 2016;98-B:1597-603. ©2016 The British Editorial Society of Bone & Joint Surgery.

The obturator oblique and iliac oblique/outlet views predict most accurately the adequate position of an anterior column acetabular screw.

PubMed

Guimarães, João Antonio Matheus; Martin, Murphy P; da Silva, Flávio Ribeiro; Duarte, Maria Eugenia Leite; Cavalcanti, Amanda Dos Santos; Machado, Jamila Alessandra Perini; Mauffrey, Cyril; Rojas, David

2018-06-08

Percutaneous fixation of the acetabulum is a treatment option for select acetabular fractures. Intra-operative fluoroscopy is required, and despite various described imaging strategies, it is debatable as to which combination of fluoroscopic views provides the most accurate and reliable assessment of screw position. Using five synthetic pelvic models, an experimental setup was created in which the anterior acetabular columns were instrumented with screws in five distinct trajectories. Five fluoroscopic images were obtained of each model (Pelvic Inlet, Obturator Oblique, Iliac Oblique, Obturator Oblique/Outlet, and Iliac Oblique/Outlet). The images were presented to 32 pelvic and acetabular orthopaedic surgeons, who were asked to draw two conclusions regarding screw position: (1) whether the screw was intra-articular and (2) whether the screw was intraosseous in its distal course through the bony corridor. In the assessment of screw position relative to the hip joint, accuracy of surgeon's response ranged from 52% (iliac oblique/outlet) to 88% (obturator oblique), with surgeon confidence in the interpretation ranging from 60% (pelvic inlet) to 93% (obturator oblique) (P < 0.0001). In the assessment of intraosseous position of the screw, accuracy of surgeon's response ranged from 40% (obturator oblique/outlet) to 79% (iliac oblique/outlet), with surgeon confidence in the interpretation ranging from 66% (iliac oblique) to 88% (pelvic inlet) (P < 0.0001). The obturator oblique and obturator oblique/outlet views afforded the most accurate and reliable assessment of penetration into the hip joint, and intraosseous position of the screw was most accurately assessed with pelvic inlet and iliac oblique/outlet views. Clinical Question.

Influence of soft tissue in the assessment of the primary fixation of acetabular cup implants using impact analyses.

PubMed

Bosc, Romain; Tijou, Antoine; Rosi, Giuseppe; Nguyen, Vu-Hieu; Meningaud, Jean-Paul; Hernigou, Philippe; Flouzat-Lachaniette, Charles-Henri; Haiat, Guillaume

2018-06-01

The acetabular cup (AC) implant primary stability is an important determinant for the success of cementless hip surgery but it remains difficult to assess the AC implant fixation in the clinic. A method based on the analysis of the impact produced by an instrumented hammer on the ancillary has been developed by our group (Michel et al., 2016a). However, the soft tissue thickness present around the acetabulum may affect the impact response, which may hamper the robustness of the method. The aim of this study is to evaluate the influence of the soft tissue thickness (STT) on the acetabular cup implant primary fixation evaluation using impact analyses. To do so, different AC implants were inserted in five bovine bone samples. For each sample, different stability conditions were obtained by changing the cavity diameter. For each configuration, the AC implant was impacted 25 times with 10 and 30 mm of soft tissues positioned underneath the sample. The averaged indicator I m was determined based on the amplitude of the signal for each configuration and each STT and the pull-out force was measured. The results show that the resonance frequency of the system increases when the value of the soft tissue thickness decreases. Moreover, an ANOVA analysis shows that there was no significant effect of the value of soft tissue thickness on the values of the indicator I m (F = 2.33; p-value = 0.13). This study shows that soft tissue thickness does not appear to alter the prediction of the acetabular cup implant primary fixation obtained using the impact analysis approach, opening the path towards future clinical trials. Copyright © 2018 Elsevier Ltd. All rights reserved.

Pelvic reconstructions following peri-acetabular bone tumour resections using a cementless ice-cream cone prosthesis with dual mobility cup.

PubMed

Issa, Samir-Pierre; Biau, David; Babinet, Antoine; Dumaine, Valérie; Le Hanneur, Malo; Anract, Philippe

2018-01-27

Despite numerous reconstructive techniques and prosthetic devices, pelvic reconstructions following peri-acetabular malignant tumours resections are highly challenging. In the present study, we describe our experience with the Integra® (Lépine, Genay, France) ice-cream cone prosthesis in such indications. The objective was to assess the mid-term outcomes of this device. Twenty-four patients' chart with peri-acetabular malignant tumours, who underwent types II or II + III peri-acetabular resections according to Enneking and Dunham with subsequent reconstruction using the Integra® prosthesis between February 2009 and February 2015, were reviewed. Seventeen cases were primary surgeries and seven cases were revisions (i.e., failures of previous reconstructions for pelvic tumours). All living patients with the prosthesis implanted were functionally assessed, using the musculoskeletal tumour society (MSTS) and Postel-Merle d'Aubigné (PMA) scores. After a mean follow-up of 49 ± 26 months (range, 8 to 94 months), 21 patients were alive (88%), including 15 patients continuously disease-free (63%). MSTS and PMA scores averaged 72 ± 13% (range, 43 to 87%) and 14.6 ± 2.6 (range, 9 to 18), respectively. Fourteen patients (58%) presented at least one complication during follow-up, including four cases of deep infection (17%), four cases of dislocation (17%), and two mechanical failures (8%). At 5 years, the implant survival rate was 75%. In comparison to previous reconstructive techniques that we used in similar indications, functional and oncologic outcomes were improved with the Integra® implant. However, as commonly observed in pelvic bone tumour surgery, complication rates remain significant. Therapeutic, Level IV-Retrospective Cases Series.

The design, production and clinical application of 3D patient-specific implants with drilling guides for acetabular surgery.

PubMed

Merema, B J; Kraeima, J; Ten Duis, K; Wendt, K W; Warta, R; Vos, E; Schepers, R H; Witjes, M J H; IJpma, F F A

2017-11-01

An innovative procedure for the development of 3D patient-specific implants with drilling guides for acetabular fracture surgery is presented. By using CT data and 3D surgical planning software, a virtual model of the fractured pelvis was created. During this process the fracture was virtually reduced. Based on the reduced fracture model, patient-specific titanium plates including polyamide drilling guides were designed, 3D printed and milled for intra-operative use. One of the advantages of this procedure is that the personalised plates could be tailored to both the shape of the pelvis and the type of fracture. The optimal screw directions and sizes were predetermined in the 3D model. The virtual plan was translated towards the surgical procedure by using the surgical guides and patient-specific osteosynthesis. Besides the description of the newly developed multi-disciplinary workflow, a clinical case example is presented to demonstrate that this technique is feasible and promising for the operative treatment of complex acetabular fractures. Copyright © 2017 Elsevier Ltd. All rights reserved.

Acetabular cup position and risk of dislocation in primary total hip arthroplasty

PubMed Central

Seagrave, Kurt G; Troelsen, Anders; Malchau, Henrik; Husted, Henrik; Gromov, Kirill

2017-01-01

Background and purpose — Hip dislocation is one of the most common complications following total hip arthroplasty (THA). Several factors that affect dislocation have been identified, including acetabular cup positioning. Optimal values for cup inclination and anteversion are debatable. We performed a systematic review to describe the different methods for measuring cup placement, target zones for cup positioning, and the association between cup positioning and dislocation following primary THA. Methods — A systematic search of literature in the PubMed database was performed (January and February 2016) to identify articles that compared acetabular cup positioning and the risk of dislocation. Surgical approach and methods for measurement of cup angles were also considered. Results— 28 articles were determined to be relevant to our research question. Some articles demonstrated that cup positioning influenced postoperative dislocation whereas others did not. The majority of articles could not identify a statistically significant difference between dislocating and non-dislocating THA with regard to mean angles of cup anteversion and inclination. Most of the articles that assessed cup placement within the Lewinnek safe zone did not show a statistically significant reduction in dislocation rate. Alternative target ranges have been proposed by several authors. Interpretation— The Lewinnek safe zone could not be justified. It is difficult to draw broad conclusions regarding a definitive target zone for cup positioning in THA, due to variability between studies and the likely multifactorial nature of THA dislocation. Future studies comparing cup positioning and dislocation rate should investigate surgical approach separately. Standardized tools for measurement of cup positioning should be implemented to allow comparison between studies. PMID:27879150

Acetabular shell deformation as a function of shell stiffness and bone strength.

PubMed

Dold, Philipp; Pandorf, Thomas; Flohr, Markus; Preuss, Roman; Bone, Martin C; Joyce, Tom J; Holland, James; Deehan, David

2016-04-01

Press-fit acetabular shells used for hip replacement rely upon an interference fit with the bone to provide initial stability. This process may result in deformation of the shell. This study aimed to model shell deformation as a process of shell stiffness and bone strength. A cohort of 32 shells with two different wall thicknesses (3 and 4 mm) and 10 different shell sizes (44- to 62-mm outer diameter) were implanted into eight cadavers. Shell deformation was then measured in the cadavers using a previously validated ATOS Triple Scan III optical system. The shell-bone interface was then considered as a spring system according to Hooke's law and from this the force exerted on the shell by the bone was calculated using a combined stiffness consisting of the measured shell stiffness and a calculated bone stiffness. The median radial stiffness for the 3-mm wall thickness was 4192 N/mm (range, 2920-6257 N/mm), while for the 4-mm wall thickness the median was 9633 N/mm (range, 6875-14,341 N/mm). The median deformation was 48 µm (range, 3-187 µm), while the median force was 256 N (range, 26-916 N). No statistically significant correlation was found between shell stiffness and deformation. Deformation was also found to be not fully symmetric (centres 180° apart), with a median angle discrepancy of 11.5° between the two maximum positive points of deformation. Further work is still required to understand how the bone influences acetabular shell deformation. © IMechE 2016.

Long-term retrospective study on the placement of the cementless acetabular cup and clinical outcomes in patients undergoing femoral head autografting for hip dysplasia and total hip arthroplasty.

PubMed

Ozden, Vahit Emre; Dikmen, Goksel; Beksac, Burak; Tozun, Ismail Remzi

2018-05-01

Placement of acetabular cup in the dysplastic hip is a challenging procedure. Using bulk femoral head autograft to increase the bony coverage of the cup is one of the techniques, which have been described. The impact of cup position on cup and autograft survival is a controversial issue. We aimed to determine whether the position of cementless acetabular cup used in conjunction with femoral head autograft in dysplastic hips affected the autograft-host incorporation with its final radiographic appearance and the cup survivorship into the second decade. Thirty-eight dysplastic hips with varying Crowe types in 31 patients (30 women and one man) were included. The mean age was 47 years (range, 29-64 years) and the mean follow-up was 20.3 years (range, 14.8-25.9 years). The initial postoperative and final radiographs were evaluated. The survival rate of the cups was analysed using Kaplan-Meier statistics and the log-rank test. Multivariate analysis was used to evaluate the effect of variables (Crowe type, radiographic initial host bone coverage over the cup and position of the cup) on survivorship. The acetabular cups were positioned anatomical in 27/38 hips according to Ranawat measurement technique. Trabecular bridging at graft-host interface was seen in all cases at an average 22.1 months. Neither acetabular cup position nor initial host bone coverage over acetabular cup less than 50% had any significant effect on either cup survival or final radiographic appearance of the graft. The 20-year cup survival rate without aseptic revision was 66% (95 CI, 52%-84%). No revision was performed due to graft resorption. Twenty-year survival rate of the cementless cup combination with femoral head autograft showed no significant differences whether it was placed at high or anatomic hip centre. The final radiographic appearance of the autograft was not affected from either the cup location or the initial radiographic horizontal host bone coverage. Copyright © 2018 The Japanese

[BIOMECHANICAL COMPARATIVE STUDY ON FOUR INTERNAL FIXATIONS FOR ACETABULAR FRACTURES IN QUADRILATERAL AREA].

PubMed

Wang, Lei; Wu, Xiaobo; Qi, Wei; Wang, Yongbin; He, Quanjie; Xu, Fengsong; Liu, Hongyang

2015-10-01

To compare the biomechanical difference of 4 kinds of internal fixations for acetabular fracture in quadrilateral area. The transverse fracture models were created in 16 hemipelves specimens from 8 adult males, and were randomly divided into 4 groups according to different internal fixation methods (n = 4): infrapectineal buttress reconstruction plate (group A), infrapectineal buttress locking reconstruction plate (group B), reconstruction plate combined with trans-plate quadrilateral screws (group C), and anterior reconstruction plate-lag screw (group D). Then the horizontal displacement, longitudinal displacement of fractures, and axial stiffness were measured and counted to compare the stability after continuous vertical loading. Under the same loading, the horizontal and longitudinal displacements of groups A, B, C, and D were decreased gradually; when the loading reached 1 800 N, the longitudinal displacement of group A was more than 3.00 mm, indicating the failure criterion, while the axial stiffness increased gradually. Under 200 N loading, there was no significant difference (P > 0.05) in horizontal displacement, longitudinal displacement, and axial stiffness among 4 groups. When the loading reached 600-1 800 N, significant differences were found in horizontal displacement, longitudinal displacement, and axial stiffness among 4 groups (P < 0.05) except the horizontal displacement between groups C and D (P > 0.05). For acetabular fracture in the quadrilateral area, anterior reconstruction plate-lag screw for internal fixation has highest stability, followed by reconstruction plate combined with trans-plate quadrilateral screws, and they are better than infrapectineal buttress reconstruction plate and infrapectineal buttress locking reconstruction plate.

[Total hip arthroplasty in post-dysplastic hip arthritis. Can type and position of the acetabular component influence longevity of the prosthesis?].

PubMed

Fousek, J; Indráková, P

2007-02-01

The aim of the study was a retrospective evaluation of our patients with post-dysplastic hips treated by cemented or non-cemented total hip arthroplasty (THA) in order to ascertain which type and position of the acetabular component was most effective. In the years 1999-2002, 111 THA procedures were performed in 93 patients, 76 women and 17 men, with post-dysplastic hip arthritis. The average age of the patients at the time of implantation was 52.6 years. On the basis of pre-operative radiographic findings, the patients' conditions were evaluated using the Hartofilakidis classification into three disease categories: dysplasia, low dislocation and high dislocation, and the patients were placed in two groups. Group 1 included 78 patients, and group 2 comprised 26 patients. None of our patients was classified as having high dislocation. Thirty-nine of these patients had previously undergone surgery for dysplastic hips. A total of 104 THAs were evaluated, because radiographic data was incomplete in seven cases. In addition to X-ray findings, the prosthesis type (cemented, hybrid, non-cemented), post-operative complications and signs of loosening were included in the evaluation. Clinical outcomes were assessed by the Harris score. The follow-up terminating on 31st December 2005 was 67 months on the average. In group 1 patients, the average Harris score increased from 38.6 to 80.3 points and in group 2 patients from 35.5 to 84.9 points, mostly with excellent and good results. In 72.1 % of the hips, a press-fit acetabular component was implanted. In 55.8 % of the cases, the acetabular component was implanted off the anatomical center of rotation, into the high hip center, with the range from 9 to 20 mm and an average of 15 mm. The average limb lengthening was 2.5 cm, ranging from 1.0 to 3.5 cm. Our results show that it is more effective to use non-cemented THA for post-dysplastic hips. The implantation of a noncemented acetabular component into the high center provides

Fretting and Corrosion at the Backside of Modular Cobalt Chromium Acetabular Inserts: A Retrieval Analysis.

PubMed

Tarity, T David; Koch, Chelsea N; Burket, Jayme C; Wright, Timothy M; Westrich, Geoffrey H

2017-03-01

Adverse local tissue reaction formation has been suggested to occur with the Modular Dual Mobility (MDM) acetabular design. Few reports in the literature have evaluated fretting and corrosion damage between the acetabular shell and modular metal inserts in this modular system. We evaluated a series of 18 retrieved cobalt chromium MDM inserts for evidence of fretting and corrosion. We assessed the backsides of 18 MDM components for evidence of fretting and corrosion in polar and taper regions based on previously established methods. We collected and assessed 30 similarly designed modular inserts retrieved from metal-on-metal (MoM) total hip arthroplasties as a control. No specific pattern of fretting or corrosion was identified on the MDM inserts. Both fretting and corrosion were significantly greater in the MoM cohort than the MDM cohort, driven by higher fretting and corrosion scores in the engaged taper region of the MoM inserts. MoM components demonstrated more fretting and corrosion than MDM designs, specifically at the taper region, likely driven by differences in the taper engagement mechanism and geometry among the insert designs. The lack of significant fretting and corrosion observed in the MDM inserts are inconsistent with recent claims that this interface may produce clinically significant metallosis and adverse local tissue reactions. Copyright © 2016 Elsevier Inc. All rights reserved.

Failure mechanisms and closed reduction of a constrained tripolar acetabular liner.

PubMed

Robertson, William J; Mattern, Christopher J; Hur, John; Su, Edwin P; Pellicci, Paul M

2009-02-01

Unlike traditional bipolar constrained liners, the Osteonics Omnifit constrained acetabular insert is a tripolar device, consisting of an inner bipolar bearing articulating within an outer, true liner. Every reported failure of the Omnifit tripolar implant has been by failure at the shell-bone interface (Type I failure), failure at the shell-liner interface (Type II failure), or failure of the locking mechanism resulting in dislocation of the bipolar-liner interface (Type III failure). In this report we present two cases of failure of the Omnifit tripolar at the bipolar-femoral head interface. To our knowledge, these are the first reported cases of failure at the bipolar-femoral head interface (Type IV failure). In addition, we described the first successful closed reduction of a Type IV failure.

Jupiter's Main Ring/Ring Halo

NASA Technical Reports Server (NTRS)

1997-01-01

A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (28.5 miles) per picture element (pixel) along Jupiter's rings. Because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow, peering back toward the Sun; the ring was approximately 2.3 million kilometers (1.4 million miles) away. The arc on the far right of the image is produced when sunlight is scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age.

Jupiter's ring system is composed of three parts - - a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, outside the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the figure's far left side. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow. Some radial structure is barely visible across the ring's ansa (top image). A faint mist of particles can be seen above and below the main rings. This vertically extended 'halo' is unusual in planetary rings, and is probably caused by electromagnetic forces pushing the smallest grains out of the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. To accentuate faint features in the bottom image of the ring halo, different brightnesses are shown through color. Brightest features are white or yellow and the

High proximal migration in cemented acetabular revisions operated with bone impaction grafting; 47 revision cups followed with RSA for 17 years.

PubMed

Mohaddes, Maziar; Herberts, Peter; Malchau, Henrik; Johanson, Per-Erik; Kärrholm, Johan

2017-05-12

Bone impaction grafting is a biologically and mechanically appealing option in acetabular revision surgery, allowing restitution of the bone stock and restoration of the biomechanics. We analysed differences in proximal migration of the revision acetabular components when bone impaction grafting is used together with a cemented or an uncemented cup. 43 patients (47 hips), revised due to acetabular loosening and judged to have less than 50% host bone-implant contact were included. The hips were randomised to either an uncemented (n = 20) or a cemented (n = 27) revision cup. Radiostereometry and radiography was performed postoperatively, at 3 and 6 months, 1, 2, 3, 5, 7, 10 and 13 and 17 years postoperatively. Clinical follow-up was performed at 1, 2 and 5 years postoperatively and thereafter at the same interval as in the radiographic follow-up. There were no differences in the base line demographic data between the 2 groups. At the last follow-up (17 years) 14 hips (10 cemented, 4 uncemented) had been re-revised due to loosening. 3 additional cups (1 uncemented and 2 cemented) were radiographically loose. There was a higher early proximal migration in the cemented cups. Cups operated on with cement showed a higher early migration measured with RSA and also a higher number of late revisions. The reason for this is not known, but factors such as inclusion of cases with severe bone defects, use of smaller bone chips and issues related to the impaction technique might have had various degrees of influence.

Boroxol rings from diffraction data on vitreous boron trioxide.

PubMed

Soper, Alan K

2011-09-14

There has been a considerable debate about the nature of the short range atomic order in vitreous B(2)O(3). Some authorities state that it is not possible to build a model of glassy boron oxide of the correct density containing a large number of six-membered rings which also fits experimental diffraction data, but recent computer simulations appear to overrule that view. To discover which view is correct I use empirical potential structure refinement (EPSR) on existing neutron and x-ray diffraction data to build two models of vitreous B(2)O(3). One of these consists only of single boron and oxygen atoms arranged in a network to reproduce the diffraction data as closely as possible. This model has less than 10% of boron atoms in boroxol rings. The second model is made up of an equimolar mixture of B(3)O(3) hexagonal ring 'molecules' and BO(3) triangular molecules, with no free boron or oxygen atoms. This second model therefore has 75% of the boron atoms in boroxol rings. It is found that both models give closely similar diffraction patterns, suggesting that the diffraction data in this case are not sensitive to the number of boroxol rings present in the structure. This reinforces recent Raman, ab initio, and NMR claims that the percentage of boroxol rings in this material may be as high as 75%. The findings of this study probably explain why some interpretations based on different simulation techniques only find a small fraction of boroxol rings. The results also highlight the power of EPSR for the extraction of accurate atomistic representations of amorphous structures, provided adequate additional, non-scattering data (such as Raman and NMR in this case) are available.

The influence of the acetabular labrum seal, intact articular superficial zone and synovial fluid thixotropy on squeeze-film lubrication of a spherical synovial joint.

PubMed

Hlavácek, M

2002-10-01

A model of synovial fluid (SF) filtration by articular cartilage (AC) in a step-loaded spherical synovial joint at rest is presented. The effects of joint pathology (such as a depleted acetabular labrum, a depleted cartilage superficial zone consistent with early osteoarthritis and an inflammatory SF) on the squeezed synovial film are also investigated. Biphasic mixture models for AC (ideal fluid and elastic porous transversely isotropic two-layer matrix) and for SF (ideal and thixotropic fluids) are applied and the following results are obtained. If the acetabular labrum is able to seal the pressurised SF between the articular surfaces (as in the normal hip joint), the fluid in the synovial film and in the cartilage within the labral ring is homogeneously pressurised. The articular surfaces remain separated by a fluid film for minutes. If the labrum is destroyed or absent and the SF can escape across the contact edge, the fluid pressure is non-homogeneous and with a small jump at the articular surface at the very moment of load application. The ensuing synovial film filtration by porous cartilage is lower for the normal cartilage (with the intact superficial zone) than if this zone is already depleted or rubbed off as in the early stage of primary osteoarthritis. Compared with the inflammatory (Newtonian) SF, the normal (thixotropic) fluid applies favourably in the squeezed film near the contact centre only, yielding a thicker SF film there, but not affecting the minimum thickness in the fluid film profile at a fixed time. For all that, in the unsealed case for both the normal and pathological joint, the macromolecular concentration of the hyaluronic acid-protein complex in the synovial film quickly increases due to the filtration in the greater part of the contact. A stable synovial gel film, thick on the order of 10(-7)m, protecting the articular surfaces from the intimate contact, is formed within a couple of seconds. Boundary lubrication by the synovial gel is

Planetary Rings

NASA Astrophysics Data System (ADS)

Esposito, Larry

2014-03-01

Preface: a personal view of planetary rings; 1. Introduction: the allure of the ringed planets; 2. Studies of planetary rings 1610-2013; 3. Diversity of planetary rings; 4. Individual ring particles and their collisions; 5. Large-scale ring evolution; 6. Moons confine and sculpt rings; 7. Explaining ring phenomena; 8. N-body simulations; 9. Stochastic models; 10. Age and evolution of rings; 11. Saturn's mysterious F ring; 12. Uranus' rings and moons; 13. Neptune's partial rings; 14. Jupiter's ring-moon system after Galileo and New Horizons; 15. Ring photometry; 16. Dusty rings; 17. Concluding remarks; Afterword; Glossary; References; Index.

Preliminary application of computer-assisted patient-specific acetabular navigational template for total hip arthroplasty in adult single development dysplasia of the hip.

PubMed

Zhang, Yuan Z; Chen, Bin; Lu, Sheng; Yang, Yong; Zhao, Jian M; Liu, Rui; Li, Yan B; Pei, Guo X

2011-12-01

The considerable variation in anatomical abnormalities of hip joints associated with different types of developmental dysplasia of hip (DDH) makes reconstruction in total hip arthroplasty (THA) difficult. It is desirable to create patient-specific designs for THA procedures. In the cases of adult single DDH, an accuracy-improved method has been developed for acetabular cup prosthesis implantation of hip arthroplasty. From October 2007 to November 2008, 22 patients with single DDH (according to the Crowe standard, all dysplasia hips were classified as type I) were scanned with spiral CT pre-operatively. These patients scheduled for THA were randomly assigned to undergo either conventional THA (control group, n = 11) or navigation template implantation (NT group, n = 11). In the NT group, three-dimensional (3D) CT pelvis image data were transferred to a computer workstation and 3D models of the hip were reconstructed using the Mimics software. The 3D models were then processed by the Imageware software. In brief, a template that best fitted the location and shape of the acetabular cup was 'reversely' built from the 3D model, the rotation centre of the pathological hip determined by mirroring that of the healthy site, and a guiding hole in the template was then designed. The navigational templates were manufactured using a rapid prototyping machine. These navigation templates guide acetabular component placement. Based on the predetermined abduction angle 45° and anteversion angle 18°, after 1 year follow-up, the NT group showed significantly smaller differences (1.6° ± 0.4°, 1.9° ± 1.1°) from the predetermined angles than those in the control group (5.8° ± 2.9°, 3.9° ± 2.5°) (P < 0.05). The template designs facilitated accurate placement of acetabular components in dysplasia of acetabulum. The hip's center of rotation in DDH could be established using computer-aided design, which provides a useful method for the accurate

Saturn's Rings and Associated Ring Plasma Cavity: Evidence for Slow Ring Erosion

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Kurth, W. S.; Gurnett, D. A.; Persoon, A. M.; MacDowall, R. J.

2017-01-01

We re-examine the radio and plasma wave observations obtained during the Cassini Saturn orbit insertion period, as the spacecraft flew over the northern ring surface into a radial distance of 1.3 Rs (over the C-ring). Voyager era studies suggest the rings are a source of micro-meteoroid generated plasma and dust, with theorized peak impact-created plasma outflows over the densest portion of the rings (central B-ring). In sharp contrast, the Cassini Radio and Plasma Wave System (RPWS) observations identify the presence of a ring-plasma cavity located in the central portion of the B-ring, with little evidence of impact-related plasma. While previous Voyager era studies have predicted unstable ion orbits over the C- ring, leading to field-aligned plasma transport to Saturns ionosphere, the Cassini RPWS observations do not reveal evidence for such instability-created plasma fountains. Given the passive ring loss processes observed by Cassini, we find that the ring lifetimes should extend >10(exp 9) years, and that there is limited evidence for prompt destruction (loss in <100 Myrs).

Saturn's rings and associated ring plasma cavity: Evidence for slow ring erosion

NASA Astrophysics Data System (ADS)

Farrell, W. M.; Kurth, W. S.; Gurnett, D. A.; Persoon, A. M.; MacDowall, R. J.

2017-08-01

We re-examine the radio and plasma wave observations obtained during the Cassini Saturn orbit insertion period, as the spacecraft flew over the northern ring surface into a radial distance of 1.3 Rs (over the C-ring). Voyager era studies suggest the rings are a source of micro-meteoroid generated plasma and dust, with theorized peak impact-created plasma outflows over the densest portion of the rings (central B-ring). In sharp contrast, the Cassini Radio and Plasma Wave System (RPWS) observations identify the presence of a ring-plasma cavity located in the central portion of the B-ring, with little evidence of impact-related plasma. While previous Voyager era studies have predicted unstable ion orbits over the C-ring, leading to field-aligned plasma transport to Saturn's ionosphere, the Cassini RPWS observations do not reveal evidence for such instability-created plasma 'fountains'. Given the passive ring loss processes observed by Cassini, we find that the ring lifetimes should extend >109 years, and that there is limited evidence for prompt destruction (loss in <100 Myrs).

Secondary reinforcement and number of primary reinforcements1

PubMed Central

Fantino, Edmund; Herrnstein, R. J.

1968-01-01

Pigeons' pecks on either of two concurrently available response keys produced secondary reinforcers according to independent one-minute variable-interval schedules. Different secondary reinforcers, in the presence of which the rates of primary reinforcement were equal, were associated with each key. The rate of pecking maintained by each secondary reinforcer varied directly, but nonproportionally, with the number of primary reinforcements given in the presence of the secondary reinforcer. PMID:5636860

Posterosuperior Placement of a Standard-Sized Cup at the True Acetabulum in Acetabular Reconstruction of Developmental Dysplasia of the Hip With High Dislocation.

PubMed

Xu, Jiawei; Xu, Chen; Mao, Yuanqing; Zhang, Jincheng; Li, Huiwu; Zhu, Zhenan

2016-06-01

We sought to evaluate posterosuperior placement of the acetabular component at the true acetabulum during acetabular reconstruction in patients with Crowe type-IV developmental dysplasia of the hip. Using pelvic computed tomography and image processing, we developed a two-dimensional mapping technique to demonstrate the distribution of preoperative three-dimensional cup coverage at the true acetabulum, determined the postoperative location of the acetabular cup, and calculated postoperative three-dimensional coverage for 16 Crowe type-IV dysplastic hips in 14 patients with a mean age of 52 years (33-78 years) who underwent total hip arthroplasty. Mean follow-up was 6.3 years (5.5-7.3 years). On preoperative mapping, the maximum three-dimensional coverage using a 44-mm cup was 87.31% (77.36%-98.14%). Mapping enabled the successful replacement of 16 hips using a mean cup size of 44.13 mm (42-46 mm) with posterosuperior placement of the cup. Early weight-bearing and no prosthesis revision or loosening during follow-up were achieved in all patients. The postoperative two-dimensional coverage on anteroposterior radiographs and three-dimensional coverage were 96.15% (89.49%-100%) and 83.42% (71.81%-98.50%), respectively. This technique may improve long-term implant survival in patients with Crowe-IV developmental dysplasia of the hip undergoing total hip arthroplasty by allowing the use of durable bearings, increasing host bone coverage, ensuring initial stability, and restoring the normal hip center. Copyright © 2015 Elsevier Inc. All rights reserved.

Planetary Rings

NASA Astrophysics Data System (ADS)

Esposito, Larry W.

2011-07-01

Preface; 1. Introduction: the allure of ringed planets; 2. Studies of planetary rings 1610-2004; 3. Diversity of planetary rings; 4. Individual ring particles and their collisions; 5. Large-scale ring evolution; 6. Moons confine and sculpt rings; 7. Explaining ring phenomena; 8. N-Body simulations; 9. Stochastic models; 10. Age and evolution of rings; 11. Saturn's mysterious F ring; 12. Neptune's partial rings; 13. Jupiter's ring-moon system after Galileo; 14. Ring photometry; 15. Dusty rings; 16. Cassini observations; 17. Summary: the big questions; Glossary; References; Index.

Accessing 3D Location of Standing Pelvis: Relative Position of Sacral Plateau and Acetabular Cavities versus Pelvis

PubMed Central

Berthonnaud, E.; Hilmi, R.; Dimnet, J.

2012-01-01

The goal of this paper is to access to pelvis position and morphology in standing posture and to determine the relative locations of their articular surfaces. This is obtained from coupling biplanar radiography and bone modeling. The technique involves different successive steps. Punctual landmarks are first reconstructed, in space, from their projected images, identified on two orthogonal standing X-rays. Geometric models, of global pelvis and articular surfaces, are determined from punctual landmarks. The global pelvis is represented as a triangle of summits: the two femoral head centers and the sacral plateau center. The two acetabular cavities are modeled as hemispheres. The anterior sacral plateau edge is represented by an hemi-ellipsis. The modeled articular surfaces are projected on each X-ray. Their optimal location is obtained when the projected contours of their models best fit real outlines identified from landmark images. Linear and angular parameters characterizing the position of global pelvis and articular surfaces are calculated from the corresponding sets of axis. Relative positions of sacral plateau, and acetabular cavities, are then calculated. Two hundred standing pelvis, of subjects and scoliotic patients, have been studied. Examples are presented. They focus upon pelvis orientations, relative positions of articular surfaces, and pelvis asymmetries. PMID:22567279

Accelerated aging, natural aging, and small punch testing of gamma-air sterilized polycarbonate urethane acetabular components.

PubMed

Kurtz, S M; Siskey, R; Reitman, M

2010-05-01

The objectives of this study were three-fold: (1) to determine the applicability of the small punch test to characterize Bionate 80A polycarbonate urethane (PCU) acetabular implants; (2) to evaluate the susceptibility of PCU acetabular implants to exhibit degradation of mechanical behavior following gamma irradiation in air and accelerated aging; and (3) to compare the oxidation of gamma-air sterilized PCU following accelerated aging and 5 years of natural shelf aging. In addition to attenuated total reflectance-Fourier transform infrared spectroscopy, we also adapted a miniature specimen mechanical test, the small punch test, for the deformable PCU cups. Accelerated aging was performed using ASTM F2003, a standard test that represents a severe oxidative challenge. The results of this study suggest that the small punch test is sufficiently sensitive and reproducible to discriminate slight differences in the large-deformation mechanical behavior of Bionate 80A following accelerated aging. The gamma-air sterilized PCU had a reduction of 9% in ultimate load after aging. Five years of shelf aging had little effect on the mechanical properties of the PCU. Overall, our findings suggest that the Bionate 80A material has greater oxidative stability than ultra-high molecular weight polyethylene following gamma irradiation in air and exposure to a severe oxidative challenge. (c) 2010 Wiley Periodicals, Inc.

Risk factors for unsuccessful acetabular press-fit fixation at primary total hip arthroplasty.

PubMed

Brulc, U; Antolič, V; Mavčič, B

2017-11-01

Surgeon at primary total hip arthroplasty sometimes cannot achieve sufficient cementless acetabular press-fit fixation and must resort to other fixation methods. Despite a predominant use of cementless cups, this issue is not fully clarified, therefore we performed a large retrospective study to: (1) identify risk factors related to patient or implant or surgeon for unsuccessful intraoperative press-fit; (2) check for correlation between surgeons' volume of operated cases and the press-fit success rate. Unsuccessful intra-operative press-fit more often occurs in older female patients, particular implants, due to learning curve and low-volume surgeons. Retrospective observational cohort of prospectively collected intraoperative data (2009-2016) included all primary total hip arthroplasty patients with implant brands that offered acetabular press-fit fixation only. Press-fit was considered successful if acetabulum was of the same implant brand as the femoral component without additional screws or cement. Logistic regression models for unsuccessful acetabular press-fit included patients' gender/age/operated side, implant, surgeon, approach (posterior n=1206, direct-lateral n=871) and surgery date (i.e. learning curve). In 2077 patients (mean 65.5 years, 1093 females, 1163 right hips), three different implant brands (973 ABG-II™-Stryker, 646 EcoFit™ Implantcast, 458 Procotyl™ L-Wright) were implanted by eight surgeons. Their unsuccessful press-fit fixation rates ranged from 3.5% to 23.7%. Older age (odds ratio 1.01 [95% CI: 0.99-1.02]), female gender (2.87 [95% CI: 2.11-3.91]), right side (1.44 [95% CI: 1.08-1.92]), surgery date (0.90 [95% CI: 1.08-1.92]) and particular implants were significant risk factors only in three surgeons with less successful surgical technique (higher rates of unsuccessful press-fit with Procotyl™-L and EcoFit™ [P=0.01]). Direct-lateral hip approach had a lower rate of unsuccessful press-fit than posterior hip approach (P<0.01), but

Microstructure and Mechanical Properties of Cr-SiC Particles-Reinforced Fe-Based Alloy Coating

NASA Astrophysics Data System (ADS)

Wang, Fu-cheng; Du, Xiao-dong; Zhan, Ma-ji; Lang, Jing-wei; Zhou, Dan; Liu, Guang-fu; Shen, Jian

2015-12-01

In this study, SiC particles were first coated with Cr to form a layer that can protect the SiC particles from dissolution in the molten pool. Then, the Cr-SiC powder was injected into the tail of molten pool during plasma-transferred arc welding process (PTAW), where the temperature was relatively low, to prepare Cr-SiC particles reinforced Fe-based alloy coating. The microstructure and phase composition of the powder and surface coatings were analyzed, and the element distribution and hardness at the interfacial region were also evaluated. The protective layer consists of Cr3Si, Cr7C3, and Cr23C6, which play an important role in the microstructure and mechanical properties. The protective layer is dissolved in the molten pool forming a flocculent region and a transition region between the SiC particles and the matrix. The tribological performance of the coating was also assessed using a ring-block sliding wear tester with GGr15 grinding ring under 490 and 980 N load. Cr-SiC particles-reinforced coating has a lower wear rate than the unreinforced coating.

The effect of dynamic hip motion on the micromotion of press-fit acetabular cups in six degrees of freedom.

PubMed

Crosnier, Emilie A; Keogh, Patrick S; Miles, Anthony W

2016-08-01

The hip joint is subjected to cyclic loading and motion during activities of daily living and this can induce micromotions at the bone-implant interface of cementless total hip replacements. Initial stability has been identified as a crucial factor to achieve osseointegration and long-term survival. Whilst fixation of femoral stems achieves good clinical results, the fixation of acetabular components remains a challenge. In vitro methods assessing cup stability keep the hip joint in a fixed position, overlooking the effect of hip motion. The effect of hip motion on cup micromotion using a hip motion simulator replicating hip flexion-extension and a six degrees of freedom measurement system was investigated. The results show an increase in cup micromotion under dynamic hip motion compared to Static Flexion. This highlights the need to incorporate hip motion and measure all degrees of freedom when assessing cup micromotion. In addition, comparison of two press-fit acetabular cups with different surface coatings suggested similar stability between the two cups. This new method provides a basis for a more representative protocol for future pre-clinical evaluation of different cup designs. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

Management of acetabular fractures with modified posterior approach to spare external hip rotators.

PubMed

Sarlak, Ahmet Y; Selek, Ozgur; Inanir, Murat; Musaoglu, Resul; Baran, Tuncay

2014-04-01

In the present study the quality of reduction and incidence of complications in hip external rotator sparing modified posterior approach was assessed in both simple and complex acetabular fractures. This retrospective study includes 37 patients (38 hips) with a mean age of 42.1 years (range 21-60), that had been treated for displaced acetabular fractures from June 2007 through May 2011. They were reviewed at a mean of 3 years (20-67 months). The fractures were classified according to the Letournel-Judet classification. Anatomic reduction and stable fixation of the fracture with less than 2mm residual displacement was achieved in 28 of 38 hips. At the final follow up the patients were evaluated clinically according to Merle d'Aubigne and Postel scoring system which had been modified by Matta and radiologically based on the criteria described by Matta. The clinical results were excellent in 20, good in 8, fair in 8, and poor 2 hips. Complications included two superficial local wound infection and 10 heterotopic ossification with 7 of the cases having grade I heterotopic ossification. Avascular necrosis of the femoral head was not seen in any of the 38 hips. One patient with preoperative sciatic nerve palsy had complete recovery of neurologic function. There were no cases of deep vein thrombosis or pulmonary embolism. The functional outcome was satisfactory in most of the cases and comparable with other larger series. Using the limited part of Henry's sciatic nerve exposure skin incision - working in the plane between gluteus maximus and the tensor fascia lata as in the classical Gibson approach and two portal external rotator hip sparing approach resulted in good fracture reduction without approach related complications. Copyright © 2013 Elsevier Ltd. All rights reserved.

[Progress on treatment and research of quadrilateral plate fractures of acetabular].

PubMed

Peng, Ye; Zhang, Li-hai; Tang, Pei-fu

2015-05-01

Acetabular is an important human joint for weight bearing. Quadrilateral plate is a crucial structure of medial acetabulum with special morphology and important function. Quadrilateral plate fractures are common fracture in acetabulum. Quadrilateral plate fracture is hard to expose and reduction because it is in the medial of acetabulum. At the same time,the bone in the quadrilateral plate is not easy to fixed for thinning bones and adjacent to the articular cavity. The operator should know well about the anatomy and choose the suitable internal fixation. After quadrilateral plate fractures, the femur head maybe displace medially even break into pelvis. That make reduction and treatment always be a challenge. With different kinds of fractures,the efficacy of treatment is not the same. This paper intend to review the relation of anatomic features,approaches, internal fixations, key point of treatment and efficacy.

Braided reinforced composite rods for the internal reinforcement of concrete

NASA Astrophysics Data System (ADS)

Gonilho Pereira, C.; Fangueiro, R.; Jalali, S.; Araujo, M.; Marques, P.

2008-05-01

This paper reports on the development of braided reinforced composite rods as a substitute for the steel reinforcement in concrete. The research work aims at understanding the mechanical behaviour of core-reinforced braided fabrics and braided reinforced composite rods, namely concerning the influence of the braiding angle, the type of core reinforcement fibre, and preloading and postloading conditions. The core-reinforced braided fabrics were made from polyester fibres for producing braided structures, and E-glass, carbon, HT polyethylene, and sisal fibres were used for the core reinforcement. The braided reinforced composite rods were obtained by impregnating the core-reinforced braided fabric with a vinyl ester resin. The preloading of the core-reinforced braided fabrics and the postloading of the braided reinforced composite rods were performed in three and two stages, respectively. The results of tensile tests carried out on different samples of core-reinforced braided fabrics are presented and discussed. The tensile and bending properties of the braided reinforced composite rods have been evaluated, and the results obtained are presented, discussed, and compared with those of conventional materials, such as steel.

Biomechanical analysis using FEA and experiments of a standard plate method versus three cable methods for fixing acetabular fractures with simultaneous THA.

PubMed

Aziz, Mina S R; Dessouki, Omar; Samiezadeh, Saeid; Bougherara, Habiba; Schemitsch, Emil H; Zdero, Radovan

2017-08-01

Acetabular fractures potentially account for up to half of all pelvic fractures, while pelvic fractures potentially account for over one-tenth of all human bone fractures. This is the first biomechanical study to assess acetabular fracture fixation using plates versus cables in the presence of a total hip arthroplasty, as done for the elderly. In Phase 1, finite element (FE) models compared a standard plate method versus 3 cable methods for repairing an acetabular fracture (type: anterior column plus posterior hemi-transverse) subjected to a physiological-type compressive load of 2207N representing 3 x body weight for a 75kg person during walking. FE stress maps were compared to choose the most mechanically stable cable method, i.e. lowest peak bone stress. In Phase 2, mechanical tests were then done in artificial hemipelvises to compare the standard plate method versus the optimal cable method selected from Phase 1. FE analysis results showed peak bone stresses of 255MPa (Plate method), 205MPa (Mears cable method), 250MPa (Kang cable method), and 181MPa (Mouhsine cable method). Mechanical tests then showed that the Plate method versus the Mouhsine cable method selected from Phase 1 had higher stiffness (662versus 385N/mm, p=0.001), strength (3210versus 2060N, p=0.009), and failure energy (8.8versus 6.2J, p=0.002), whilst they were statistically equivalent for interfragmentary sliding (p≥0.179) and interfragmentary gapping (p≥0.08). The Plate method had superior mechanical properties, but the Mouhsine cable method may be a reasonable alternative if osteoporosis prevents good screw thread interdigitation during plating. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

Quantification of Wear and Deformation in Different Configurations of Polyethylene Acetabular Cups Using Micro X-ray Computed Tomography

PubMed Central

Affatato, Saverio; Zanini, Filippo; Carmignato, Simone

2017-01-01

Wear is currently quantified as mass loss of the bearing materials measured using gravimetric methods. However, this method does not provide other information, such as volumetric loss or surface deviation. In this work, we validated a technique to quantify polyethylene wear in three different batches of ultrahigh-molecular-polyethylene acetabular cups used for hip implants using nondestructive microcomputed tomography. Three different configurations of polyethylene acetabular cups, previously tested under the ISO 14242 parameters, were tested on a hip simulator for an additional 2 million cycles using a modified ISO 14242 load waveform. In this context, a new approach was proposed in order to simulate, on a hip joint simulator, high-demand activities. In addition, the effects of these activities were analyzed in terms of wear and deformations of those polyethylenes by means of gravimetric method and micro X-ray computed tomography. In particular, while the gravimetric method was used for weight loss assessment, microcomputed tomography allowed for acquisition of additional quantitative information about the evolution of local wear and deformation through three-dimensional surface deviation maps for the entire cups’ surface. Experimental results showed that the wear and deformation behavior of these materials change according to different mechanical simulations. PMID:28772616

Control of intramolecular π-π stacking interaction in cationic iridium complexes via fluorination of pendant phenyl rings.

PubMed

He, Lei; Ma, Dongxin; Duan, Lian; Wei, Yongge; Qiao, Juan; Zhang, Deqiang; Dong, Guifang; Wang, Liduo; Qiu, Yong

2012-04-16

Intramolecular π-π stacking interaction in one kind of phosphorescent cationic iridium complexes has been controlled through fluorination of the pendant phenyl rings on the ancillary ligands. Two blue-green-emitting cationic iridium complexes, [Ir(ppy)(2)(F2phpzpy)]PF(6) (2) and [Ir(ppy)(2)(F5phpzpy)]PF(6) (3), with the pendant phenyl rings on the ancillary ligands substituted with two and five fluorine atoms, respectively, have been synthesized and compared to the parent complex, [Ir(ppy)(2)(phpzpy)]PF(6) (1). Here Hppy is 2-phenylpyridine, F2phpzpy is 2-(1-(3,5-difluorophenyl)-1H-pyrazol-3-yl)pyridine, F5phpzpy is 2-(1-pentafluorophenyl-1H-pyrazol-3-yl)-pyridine, and phpzpy is 2-(1-phenyl-1H-pyrazol-3-yl)pyridine. Single crystal structures reveal that the pendant phenyl rings on the ancillary ligands stack to the phenyl rings of the ppy ligands, with dihedral angles of 21°, 18°, and 5.0° between least-squares planes for complexes 1, 2, and 3, respectively, and centroid-centroid distances of 3.75, 3.65, and 3.52 Å for complexes 1, 2, and 3, respectively, indicating progressively reinforced intramolecular π-π stacking interactions from complexes 1 to 2 and 3. Compared to complex 1, complex 3 with a significantly reinforced intramolecular face-to-face π-π stacking interaction exhibits a significantly enhanced (by 1 order of magnitude) photoluminescent efficiency in solution. Theoretical calculations reveal that in complex 3 it is unfavorable in energy for the pentafluorophenyl ring to swing by a large degree and the intramolecular π-π stacking interaction remains on the lowest triplet state. © 2012 American Chemical Society

Report of the eRHIC Ring-Ring Working Group

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aschenauer, E. C.; Berg, S.; Blaskiewicz, M.

2015-10-13

This report evaluates the ring-ring option for eRHIC as a lower risk alternative to the linac-ring option. The reduced risk goes along with a reduced initial luminosity performance. However, a luminosity upgrade path is kept open. This upgrade path consists of two branches, with the ultimate upgrade being either a ring-ring or a linac-ring scheme. The linac-ring upgrade could be almost identical to the proposed linac-ring scheme, which is based on an ERL in the RHIC tunnel. This linac-ring version has been studied in great detail over the past ten years, and its significant risks are known. On the othermore » hand, no detailed work on an ultimate performance ring-ring scenario has been performed yet, other than the development of a consistent parameter set. Pursuing the ring-ring upgrade path introduces high risks and requires significant design work that is beyond the scope of this report.« less

Wear Behaviours and Oxidation Effects on Different UHMWPE Acetabular Cups Using a Hip Joint Simulator

PubMed Central

Jaber, Sami Abdel; Merola, Massimiliano

2018-01-01

Given the long-term problem of polyethylene wear, medical interest in the new improved cross-linked polyethylene (XLPE), with or without the adding of vitamin E, has risen. The main aim of this study is to gain further insights into the mutual effects of radiation cross-linking and addition of vitamin E on the wear performance of ultra-high-molecular-weight polyethylene (UHMWPE). We tested four different batches of polyethylene (namely, a standard one, a vitamin E-stabilized, and two cross-linked) in a hip joint simulator for five million cycles where bovine calf serum was used as lubricant. The acetabular cups were then analyzed using a confocal profilometer to characterize the surface topography. Moreover; the cups were analyzed by using Fourier Transformed Infrared Spectroscopy and Differential Scanning Calorimetry in order to assess the chemical characteristics of the pristine materials. Comparing the different cups’ configuration, mass loss was found to be higher for standard polyethylene than for the other combinations. Mass loss negatively correlated to the cross-link density of the polyethylenes. None of the tested formulations showed evidence of oxidative degradation. We found no correlation between roughness parameters and wear. Furthermore, we found significantly differences in the wear behavior of all the acetabular cups. XLPEs exhibited lower weight loss, which has potential for reduced wear and decreased osteolysis. However, surface topography revealed smoother surfaces of the standard and vitamin E stabilized polyethylene than on the cross-linked samples. This observation suggests incipient crack generations on the rough and scratched surfaces of the cross-linked polyethylene liners. PMID:29547536

Saturn's Rings

NASA Astrophysics Data System (ADS)

Cuzzi, J. N.

2014-12-01

The rings are changing before our eyes; structure varies on all timescales and unexpected things have been discovered. Many questions have been answered, but some answers remain elusive (see Cuzzi et al 2010 for a review). Here we highlight the major ring science progress over the mission to date, and describe new observations planned for Cassini's final three years. Ring Composition and particle sizes: The rings are nearly all water ice with no other ices - so why are they reddish? The C Ring and Cassini Division are "dirtier" than the more massive B and A Rings, as shown by near-IR and, recently, microwave observations. Particle sizes, from stellar and radio occultations, vary from place to place. Ring structure, micro and macro: numerous spiral density waves and ubiquitous "self-gravity wakes" reveal processes which fostered planet formation in the solar system and elsewhere. However, big puzzles remain regarding the main ring divisions, the C Ring plateau structures, and the B Ring irregular structure. Moonlets, inside and out, seen and unseen: Two gaps contain sizeable moonlets, but more gaps seem to contain none; even smaller embedded "propeller" objects wander, systematically or randomly, through the A ring. Rubble pile ringmoons just outside the rings may escaped from the rings, and the recently discovered "Peggy" may be trying this as we watch. Impact bombardment of the rings: Comet fragments set the rings to rippling on century-timescales, and boulders crash through hourly; meanwhile, the constant hail of infalling Kuiper belt material has a lower mass flux than previously thought. Origin and Age of the Rings: The ring mass and bombardment play key roles. The ring mass is well known everywhere but in the B Ring (where most of it is). New models suggest how tidal breakup of evolving moons may have formed massive ancient rings, of which the current ring is just a shadow. During its last three years, the Cassini tour profile will allow entirely new

Reinforcement magnitude: an evaluation of preference and reinforcer efficacy.

PubMed

Trosclair-Lasserre, Nicole M; Lerman, Dorothea C; Call, Nathan A; Addison, Laura R; Kodak, Tiffany

2008-01-01

Consideration of reinforcer magnitude may be important for maximizing the efficacy of treatment for problem behavior. Nonetheless, relatively little is known about children's preferences for different magnitudes of social reinforcement or the extent to which preference is related to differences in reinforcer efficacy. The purpose of the current study was to evaluate the relations among reinforcer magnitude, preference, and efficacy by drawing on the procedures and results of basic experimentation in this area. Three children who engaged in problem behavior that was maintained by social positive reinforcement (attention, access to tangible items) participated. Results indicated that preference for different magnitudes of social reinforcement may predict reinforcer efficacy and that magnitude effects may be mediated by the schedule requirement.

Reinforcement Magnitude: An Evaluation of Preference and Reinforcer Efficacy

PubMed Central

Trosclair-Lasserre, Nicole M; Lerman, Dorothea C; Call, Nathan A; Addison, Laura R; Kodak, Tiffany

2008-01-01

Consideration of reinforcer magnitude may be important for maximizing the efficacy of treatment for problem behavior. Nonetheless, relatively little is known about children's preferences for different magnitudes of social reinforcement or the extent to which preference is related to differences in reinforcer efficacy. The purpose of the current study was to evaluate the relations among reinforcer magnitude, preference, and efficacy by drawing on the procedures and results of basic experimentation in this area. Three children who engaged in problem behavior that was maintained by social positive reinforcement (attention, access to tangible items) participated. Results indicated that preference for different magnitudes of social reinforcement may predict reinforcer efficacy and that magnitude effects may be mediated by the schedule requirement. PMID:18595284

Planetary Rings

NASA Astrophysics Data System (ADS)

Tiscareno, Matthew S.

Planetary rings are the only nearby astrophysical disks and the only disks that have been investigated by spacecraft (especially the Cassini spacecraft orbiting Saturn). Although there are significant differences between rings and other disks, chiefly the large planet/ring mass ratio that greatly enhances the flatness of rings (aspect ratios as small as 10- 7), understanding of disks in general can be enhanced by understanding the dynamical processes observed at close range and in real time in planetary rings.We review the known ring systems of the four giant planets, as well as the prospects for ring systems yet to be discovered. We then review planetary rings by type. The A, B, and C rings of Saturn, plus the Cassini Division, comprise our solar system's only dense broad disk and host many phenomena of general application to disks including spiral waves, gap formation, self-gravity wakes, viscous overstability and normal modes, impact clouds, and orbital evolution of embedded moons. Dense narrow rings are found both at Uranus (where they comprise the main rings entirely) and at Saturn (where they are embedded in the broad disk) and are the primary natural laboratory for understanding shepherding and self-stability. Narrow dusty rings, likely generated by embedded source bodies, are surprisingly found to sport azimuthally confined arcs at Neptune, Saturn, and Jupiter. Finally, every known ring system includes a substantial component of diffuse dusty rings.Planetary rings have shown themselves to be useful as detectors of planetary processes around them, including the planetary magnetic field and interplanetary impactors as well as the gravity of nearby perturbing moons. Experimental rings science has made great progress in recent decades, especially numerical simulations of self-gravity wakes and other processes but also laboratory investigations of coefficient of restitution and spectroscopic ground truth. The age of self-sustained ring systems is a matter of

Early experience with dual mobility acetabular systems featuring highly cross-linked polyethylene liners for primary hip arthroplasty in patients under fifty five years of age: an international multi-centre preliminary study.

PubMed

Epinette, Jean-Alain; Harwin, Steven F; Rowan, Fiachra E; Tracol, Philippe; Mont, Michael A; Chughtai, Morad; Westrich, Geoffrey H

2017-03-01

To evaluate early performance of contemporary dual mobility acetabular systems with second generation annealed highly cross-linked polyethylene for primary hip arthroplasty of patients under 55 years of age. A prospective observational five years study across five centers in Europe and the USA of 321 patients with a mean age of 48.1 years was performed. Patients were assessed for causes of revision, hip instability, intra-prosthetic dissociation, Harris hip score and radiological signs of osteolysis. There were no dislocations and no intra-prosthetic dissociations. Kaplan Meier analysis demonstrated 97.51% survivorship for all cause revision and 99.68% survivorship for acetabular component revision at five years. Mean Harris hip score was 93.6. Two acetabular shells were revised for neck-rim implant impingement without dislocation and ten femoral stems were revised for causes unrelated to dual mobility implants. Contemporary highly cross-linked polyethylene dual mobility systems demonstrate excellent early clinical, radiological, and survivorship results in a cohort of patients that demand high performance from their implants. It is envisaged that DM and second generation annealed HXLPE may reduce THA instability and wear, the two most common causes of THA revision in hip arthroplasty.

Reinforced Carbon Nanotubes.

DOEpatents

Ren, Zhifen; Wen, Jian Guo; Lao, Jing Y.; Li, Wenzhi

2005-06-28

The present invention relates generally to reinforced carbon nanotubes, and more particularly to reinforced carbon nanotubes having a plurality of microparticulate carbide or oxide materials formed substantially on the surface of such reinforced carbon nanotubes composite materials. In particular, the present invention provides reinforced carbon nanotubes (CNTs) having a plurality of boron carbide nanolumps formed substantially on a surface of the reinforced CNTs that provide a reinforcing effect on CNTs, enabling their use as effective reinforcing fillers for matrix materials to give high-strength composites. The present invention also provides methods for producing such carbide reinforced CNTs.

Internal Fixation of Complicated Acetabular Fractures Directed by Preoperative Surgery with 3D Printing Models.

PubMed

Liu, Zhao-Jie; Jia, Jian; Zhang, Yin-Guang; Tian, Wei; Jin, Xin; Hu, Yong-Cheng

2017-05-01

The purpose of this article is to evaluate the efficacy and feasibility of preoperative surgery with 3D printing-assisted internal fixation of complicated acetabular fractures. A retrospective case review was performed for the above surgical procedure. A 23-year-old man was confirmed by radiological examination to have fractures of multiple ribs, with hemopneumothorax and communicated fractures of the left acetabulum. According to the Letounel and Judet classification, T-shaped fracture involving posterior wall was diagnosed. A 3D printing pelvic model was established using CT digital imaging and communications in medicine (DICOM) data preoperatively, with which surgical procedures were simulated in preoperative surgery to confirm the sequence of the reduction and fixation as well as the position and length of the implants. Open reduction with internal fixation (ORIF) of the acetabular fracture using modified ilioinguinal and Kocher-Langenbeck approaches was performed 25 days after injury. Plates that had been pre-bent in the preoperative surgery were positioned and screws were tightened in the directions determined in the preoperative planning following satisfactory reduction. The duration of the operation was 170 min and blood loss was 900 mL. Postoperative X-rays showed that anatomical reduction of the acetabulum was achieved and the hip joint was congruous. The position and length of the implants were not different when compared with those in preoperative surgery on 3D printing models. We believe that preoperative surgery using 3D printing models is beneficial for confirming the reduction and fixation sequence, determining the reduction quality, shortening the operative time, minimizing preoperative difficulties, and predicting the prognosis for complicated fractures of acetabulam. © 2017 Chinese Orthopaedic Association and John Wiley & Sons Australia, Ltd.

Quasi-reinforcement: control of responding by a percentage-reinforcement schedule1

PubMed Central

Neuringer, Allen J.; Chung, Shin-Ho

1967-01-01

When a variable-interval schedule of reinforcement was segmented into small fixed-interval components, with reinforcements following some components and brief blackouts following the others, rate of responding doubled and a positively accelerated pattern within each component was obtained. Presented according to this percentage reinforcement paradigm, the blackouts approximated the functions of a food reinforcer. These effects occurred only when the behavior sequence required to produce reinforcement was identical to that required to produce blackout. The quasi-reinforcing effects of these blackout stimuli suggest that a neutral stimulus need not occasion or accompany a primary reinforcer to acquire reinforcing properties. PMID:16811304

Ultrasound in Total Hip Replacement: Value of Anterior Acetabular Cup Visibility and Contact With the Iliopsoas Tendon.

PubMed

Guillin, Raphaël; Bertaud, Valérie; Garetier, Marc; Fantino, Olivier; Polard, Jean-Louis; Lambotte, Jean-Christophe

2018-06-01

To assess visibility of the acetabular cup in total hip replacement and to determine the value of direct and indirect signs of iliopsoas impingement syndrome with ultrasound. Ultrasound examinations were performed by a single operator in 17 patients with iliopsoas impingement syndrome and 48 control patients. Cup visibility, contact between the cup and psoas tendon, and the presence of indirect signs of iliopsoas impingement syndrome were investigated in all patients. When the acetabular cup was visible, its size and position in relation to the psoas tendon were recorded. Anterior cup visibility (P = .03), contact with the psoas tendon (P < .001), psoas tendinopathy (P = .02), and iliopsoas bursitis (P < .001) were significantly associated with iliopsoas impingement syndrome, the latter reported with specificity of 100%. In the sagittal plane at the level of the psoas tendon, a maximum sagittal length of greater than 5 mm and a posteroanterior cup shift of 3 mm or greater yielded respective sensitivities of 82% and 59% and specificities of 81% and 100%. When iliopsoas impingement syndrome is clinically suspected, the presence of iliopsoas bursitis or a posteroanterior cup shift of greater than 3 mm under the psoas tendon serve to confirm the diagnosis. In the absence of these conditions, a therapeutic test may be necessary because of the incomplete, albeit high, specificity of other signs. © 2017 by the American Institute of Ultrasound in Medicine.

Integrally Closed Rings

NASA Astrophysics Data System (ADS)

Tuganbaev, A. A.

1982-04-01

This paper studies integrally closed rings. It is shown that a semiprime integrally closed Goldie ring is the direct product of a semisimple artinian ring and a finite number of integrally closed invariant domains that are classically integrally closed in their (division) rings of fractions. It is shown also that an integrally closed ring has a classical ring of fractions and is classically integrally closed in it.Next, integrally closed noetherian rings are considered. It is shown that an integrally closed noetherian ring all of whose nonzero prime ideals are maximal is either a quasi-Frobenius ring or a hereditary invariant domain.Finally, those noetherian rings all of whose factor rings are invariant are described, and the connection between integrally closed rings and distributive rings is examined.Bibliography: 13 titles.

Mapping Ring Particle Cooling across Saturn's Rings with Cassini CIRS

NASA Astrophysics Data System (ADS)

Brooks, Shawn M.; Spilker, L. J.; Edgington, S. G.; Pilorz, S. H.; Deau, E.

2010-10-01

Previous studies have shown that the rings' thermal inertia, a measure of their response to changes in the thermal environment, varies from ring to ring. Thermal inertia can provide insight into the physical structure of Saturn's ring particles and their regoliths. Low thermal inertia and quick temperature responses are suggestive of ring particles that have more porous or fluffy regoliths or that are riddled with cracks. Solid, coherent particles can be expected to have higher thermal inertias (Ferrari et al. 2005). Cassini's Composite Infrared Spectrometer has recorded millions of spectra of Saturn's rings since its arrival at Saturn in 2004 (personal communication, M. Segura). CIRS records far infrared radiation between 10 and 600 cm-1 (16.7 and 1000 µm) at focal plane 1 (FP1), which has a field of view of 3.9 mrad. Thermal emission from Saturn's rings peaks in this wavelength range. FP1 spectra can be used to infer ring temperatures. By tracking how ring temperatures vary, we can determine the thermal inertia of the rings. In this work we focus on CIRS observations of the shadowed portion of Saturn's rings. The thermal budget of the rings is dominated by the solar radiation absorbed by its constituent particles. When ring particles enter Saturn's shadow this source of energy is abruptly cut off. As a result, ring particles cool as they traverse Saturn's shadow. From these shadow observations we can create cooling curves at specific locations across the rings. We will show that the rings' cooling curves and thus their thermal inertia vary not only from ring to ring, but by location within the individual rings. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2010 California Institute of Technology. Government sponsorship acknowledged.

Effect of viscosity of a thermoplastic prepreg and matrix upon winding of rings

NASA Astrophysics Data System (ADS)

Stavrov, V. P.; Markov, A. V.; Zhernovskii, A. V.; Friedrich, K. F.

2000-05-01

The problem of compression of a unidirectional layer and shear of a polymer interlayer during winding of rings is considered. The equations determining the dependence of the layer thickness and stresses on the parameters entering into the power flow law for a prepreg and polymer matrix and on the basic parameters of the winding process—the initial tension of the prepreg, its placement rate, and the radius of a mandrel—are derived. The ring thickness measurements obtained at various temperatures and initial tension forces of plies confirm the adequacy of the model offered. It is found that the viscous properties of the prepreg and matrix upon winding affect the relative change in the layer thickness to a greater extent than the stresses in these layers. With increase in temperature and tension force upon winding, the effect of viscous deformations of the prepreg and matrix increases. A decrease in viscosity and an increase in the tension force of the tape lead to a higher strength of the ring in tension and interlaminar shear; however, the growing percolation of the polymer melt leads to a greater inhomogeneity of the structure of the composite in the ring and to a lower reinforcing effect of the factors mentioned.

Evaluating the influence of postsession reinforcement on choice of reinforcers.

PubMed

Kodak, Tiffany; Lerman, Dorothea C; Call, Nathan

2007-01-01

Factors that influence reinforcer choice have been examined in a number of applied studies (e.g., Neef, Mace, Shea, & Shade, 1992; Shore, Iwata, DeLeon, Kahng, & Smith, 1997; Tustin, 1994). However, no applied studies have evaluated the effects of postsession reinforcement on choice between concurrently available reinforcers, even though basic findings indicate that this is an important factor to consider (Hursh, 1978; Zeiler, 1999). In this bridge investigation, we evaluated the influence of postsession reinforcement on choice of two food items when task responding was reinforced on progressive-ratio schedules. Participants were 3 children who had been diagnosed with developmental disabilities. Results indicated that response allocation shifted from one food item to the other food item under thinner schedules of reinforcement when no postsession reinforcement was provided. These findings suggest that the efficacy of instructional programs or treatments for problem behavior may be improved by restricting reinforcers outside treatment sessions.

Effectiveness of Fiber Reinforcement on the Mechanical Properties and Shrinkage Cracking of Recycled Fine Aggregate Concrete.

PubMed

Nam, Jeongsoo; Kim, Gyuyong; Yoo, Jaechul; Choe, Gyeongcheol; Kim, Hongseop; Choi, Hyeonggil; Kim, Youngduck

2016-02-26

This paper presents an experimental study conducted to investigate the effect of fiber reinforcement on the mechanical properties and shrinkage cracking of recycled fine aggregate concrete (RFAC) with two types of fiber-polyvinyl alcohol (PVA) and nylon. A small fiber volume fraction, such as 0.05% or 0.1%, in RFAC with polyvinyl alcohol or nylon fibers was used for optimum efficiency in minimum quantity. Additionally, to make a comparative evaluation of the mechanical properties and shrinkage cracking, we examined natural fine aggregate concrete as well. The test results revealed that the addition of fibers and fine aggregates plays an important role in improving the mechanical performance of the investigated concrete specimens as well as controlling their cracking behavior. The mechanical properties such as compressive strength, splitting tensile strength, and flexural strength of fiber-reinforced RFAC were slightly better than those of non-fiber-reinforced RFAC. The shrinkage cracking behavior was examined using plat-ring-type and slab-type tests. The fiber-reinforced RFAC showed a greater reduction in the surface cracks than non-fiber-reinforced concrete. The addition of fibers at a small volume fraction in RFAC is more effective for drying shrinkage cracks than for improving mechanical performance.

Effectiveness of Fiber Reinforcement on the Mechanical Properties and Shrinkage Cracking of Recycled Fine Aggregate Concrete

PubMed Central

Nam, Jeongsoo; Kim, Gyuyong; Yoo, Jaechul; Choe, Gyeongcheol; Kim, Hongseop; Choi, Hyeonggil; Kim, Youngduck

2016-01-01

This paper presents an experimental study conducted to investigate the effect of fiber reinforcement on the mechanical properties and shrinkage cracking of recycled fine aggregate concrete (RFAC) with two types of fiber—polyvinyl alcohol (PVA) and nylon. A small fiber volume fraction, such as 0.05% or 0.1%, in RFAC with polyvinyl alcohol or nylon fibers was used for optimum efficiency in minimum quantity. Additionally, to make a comparative evaluation of the mechanical properties and shrinkage cracking, we examined natural fine aggregate concrete as well. The test results revealed that the addition of fibers and fine aggregates plays an important role in improving the mechanical performance of the investigated concrete specimens as well as controlling their cracking behavior. The mechanical properties such as compressive strength, splitting tensile strength, and flexural strength of fiber-reinforced RFAC were slightly better than those of non-fiber-reinforced RFAC. The shrinkage cracking behavior was examined using plat-ring-type and slab-type tests. The fiber-reinforced RFAC showed a greater reduction in the surface cracks than non-fiber-reinforced concrete. The addition of fibers at a small volume fraction in RFAC is more effective for drying shrinkage cracks than for improving mechanical performance. PMID:28773256

The Anterior Intrapelvic Approach for Acetabular Fractures Using Approach-Specific Instruments and an Anatomical-Preshaped 3-Dimensional Suprapectineal Plate.

PubMed

Gras, Florian; Marintschev, Ivan; Grossterlinden, Lars; Rossmann, Markus; Graul, Isabel; Hofmann, Gunther O; Rueger, Johannes M; Lehmann, Wolfgang

2017-07-01

Anatomical acetabular plates the anterior intrapelvic approach (AIP) were recently introduced to fix acetabular fractures through the intrapelvic approach. Therefore, we asked the following: (1) Does the preshaped 3-dimensional suprapectineal plate interfere with or even impair the fracture reduction quality? (2) How often does the AIP approach need to be extended by the first (lateral) window of the ilioinguinal approach? Observational case series. Two Level 1 trauma centers. Patients with unstable acetabular fractures in 2014. Fracture fixation with anatomical-preshaped, 3-dimensional suprapectineal plates through the AIP approach ± the first window of the ilioinguinal approach. Fracture reduction results were measured in computed tomography scans and graded according to the Matta quality of reduction. Intraoperative parameters and perioperative complications were recorded. Radiological results (according to Matta) and functional outcome (modified Merle d'Aubigné score) were evaluated at 1-year follow-up. Thirty patients (9 women + 21 men; mean age ± SE: 64 ± 8 years) were included. The intrapelvic approach was solely used in 19 cases, and in 11 cases, an additional extension with the first window of the ilioinguinal approach (preferential for 2-column fractures) was performed. The mean operating time was 202 ± 59 minutes; the fluoroscopic time was 66 ± 48 seconds. Fracture gaps and steps in preoperative versus postoperative computed tomography scans were 12.4 ± 9.8 versus 2.0 ± 1.5 and 6.0 ± 5.5 versus 1.3 ± 1.7 mm, respectively. At 13.4 ± 2.9 months follow-up, the Matta grading was excellent in 50%, good in 25%, fair in 11%, and poor in 14% of cases. The modified Merle d'Aubigné score was excellent in 17%, good in 37%, fair in 33%, and poor in 13% of cases. The AIP approach using approach-specific instruments and an anatomical-preshaped, 3-dimensional suprapectineal plate became the standard procedure in our departments. Radiological and functional

The influence of head diameter and wall thickness on deformations of metallic acetabular press-fit cups and UHMWPE liners: a finite element analysis.

PubMed

Goebel, Paul; Kluess, Daniel; Wieding, Jan; Souffrant, Robert; Heyer, Horst; Sander, Manuela; Bader, Rainer

2013-03-01

To increase the range of motion of total hip endoprostheses, prosthetic heads need to be enlarged, which implies that the cup and/or liner thickness must decrease. This may have negative effects on the wear rate, because the acetabular cups and liners could deform during press-fit implantation and hip joint loading. We compared the metal cup and polyethylene liner deformations that occurred when different wall thicknesses were used in order to evaluate the resulting changes in the clearance of the articulating region. A parametric finite element model utilized three cup and liner wall thicknesses to analyze cup and liner deformations after press-fit implantation into the pelvic bone. The resultant hip joint force during heel strike was applied while the femur was fixed, accounting for physiological muscle forces. The deformation behavior of the liner under joint loading was therefore assessed as a function of the head diameter and the resulting clearance. Press-fit implantation showed diametral cup deformations of 0.096, 0.034, and 0.014 mm for cup wall thicknesses of 3, 5, and 7 mm, respectively. The largest deformations (average 0.084 ± 0.003 mm) of liners with thicknesses of 4, 6, and 8 mm occurred with the smallest cup wall thickness (3 mm). The smallest liner deformation (0.011 mm) was obtained with largest cup and liner wall thicknesses. Under joint loading, liner deformations in thin-walled acetabular cups (3 mm) reduced the initial clearance by about 50 %. Acetabular press-fit cups with wall thicknesses of ≤5 mm should only be used in combination with polyethylene liners >6 mm thick in order to minimize the reduction in clearance.

Evaluating The Influence of Postsession Reinforcement on Choice of Reinforcers

PubMed Central

Kodak, Tiffany; Lerman, Dorothea C; Call, Nathan

2007-01-01

Factors that influence reinforcer choice have been examined in a number of applied studies (e.g., Neef, Mace, Shea, & Shade, 1992; Shore, Iwata, DeLeon, Kahng, & Smith, 1997; Tustin, 1994). However, no applied studies have evaluated the effects of postsession reinforcement on choice between concurrently available reinforcers, even though basic findings indicate that this is an important factor to consider (Hursh, 1978; Zeiler, 1999). In this bridge investigation, we evaluated the influence of postsession reinforcement on choice of two food items when task responding was reinforced on progressive-ratio schedules. Participants were 3 children who had been diagnosed with developmental disabilities. Results indicated that response allocation shifted from one food item to the other food item under thinner schedules of reinforcement when no postsession reinforcement was provided. These findings suggest that the efficacy of instructional programs or treatments for problem behavior may be improved by restricting reinforcers outside treatment sessions. PMID:17970264

Ring dynamics

NASA Technical Reports Server (NTRS)

Borderies, Nicole

1989-01-01

Theoretical models of planetary-ring dynamics are discussed in a detailed analytical review and illustrated with graphs and diagrams. The streamline concept is introduced, and the phenomena associated with the transport of angular momentum are described. Particular attention is then given to (1) broad rings like those of Saturn (shepherding, density-wave excitation, gaps, bending-wave excitation, multiringlet structures, inner-edge shepherding, and the possibility of polar rings around Neptune), (2) narrow rings like those of Uranus (shepherding, ring shapes, and a self-gravity model of rigid precession), and (3) ring arcs like those seen in stellar-occultation observations of Neptune.

Ultimate Load Behaviour of Reinforced Concrete Beam with Corroded Reinforcement

NASA Astrophysics Data System (ADS)

Kanchana Devi, A.; Ramajaneyulu, K.; Sundarkumar, S.; Ramesh, G.; Bharat Kumar, B. H.; Krishna Moorthy, T. S.

2017-12-01

Corrosion of reinforcement reduces the load carrying capacity, energy dissipation and ductility of Reinforced Concrete (RC) members. In the present study, reinforcements of RC beam are subjected to 10, 25, and 30% corrosion and the respective RC beams are tested to evaluate their ultimate load behaviour. A huge drop in energy dissipation capacity of the RC beam is observed beyond the corrosion level of 10%. Further, nonlinear finite element analysis is employed to assess the load-displacement behaviour and ultimate load of RC beam. The corrosion induced damage to the reinforcement is represented in the finite element model by modifying its mechanical properties based on the results reported in the literature. The resultant load versus displacement curves of reinforced concrete beams are obtained. Good correlation is observed between the finite element analysis results and that obtained from experimental investigation on the control beam. The experimental results are also compared with the finite element analysis results for RC beams with corroded reinforcement. In order to understand the effect of corrosion on the mechanical properties of reinforcement, the corroded reinforcements are modelled in nonlinear finite element analysis by (i) reducing the area of reinforcement alone (ii) by reducing both area and mechanical properties and (iii) reducing the mechanical properties without reducing the area of steel as reported in literature. The results obtained for the beam with corroded reinforcement confirms reduction in yield stress and ultimate stress of the reinforcement steel.

Open reduction and internal fixation of osteoporotic acetabular fractures through the ilio-inguinal approach: use of buttress plates to control medial displacement of the quadrilateral surface.

PubMed

Peter, Robin E

2015-01-01

The number of acetabular fractures in the geriatric population requiring open reduction and internal fixation is increasing. Fractures with medial or anterior displacement are the most frequent types, and via the ilio-inguinal approach buttress plates have proved helpful to maintain the quadrilateral surface or medial acetabular wall. Seven to ten hole 3.5 mm reconstruction plates may be used as buttress plates, placed underneath the usual pelvic brim plate. This retrospective study presents our results with this technique in 13 patients at a minimum follow-up of 12 months (average, 31 months). 85% of the patients had a good result. The early onset of post-traumatic osteoarthritis necessitated total hip arthroplasty in two patients (15%) at 12 and 18 months follow-up, respectively. This treatment option should be considered in the surgeon's armamentarium when fixing these challenging cases. Copyright © 2015 Elsevier Ltd. All rights reserved.

Female Sex Is a Risk Factor for Failure of Hip Arthroscopy Performed for Acetabular Retroversion

PubMed Central

Poehling-Monaghan, Kirsten L.; Krych, Aaron J.; Levy, Bruce A.; Trousdale, Robert T.; Sierra, Rafael J.

2017-01-01

Background: The success of hip surgery in treating acetabular retroversion depends on the severity of the structural deformity and on selecting the correct patient for open or arthroscopic procedures. Purpose: To compare a group of patients with retroverted hips treated successfully with hip arthroscopy with a group of patients with retroverted hips that failed arthroscopic surgery, with special emphasis on (1) patient characteristics, (2) perioperative radiographic parameters, (3) intraoperative findings and concomitant procedures, and (4) patient sex. Study Design: Case-control study; Level of evidence, 3. Methods: We retrospectively reviewed the charts of 47 adult patients (47 hips) with acetabular retroversion who had undergone hip arthroscopy. Retroversion was based on the presence of an ischial spine sign in addition to either a crossover or posterior wall sign on a well-positioned anteroposterior pelvic radiograph. A total of 24 hips (50%) (16 females, 8 males; mean patient age, 31 years) had failed arthroscopy, defined as modified Harris Hip Score (mHHS) <80 or need for subsequent procedure. Twenty-three hips (8 females, 15 males; mean patient age, 29 years) were considered successful, defined as having no subsequent procedures and an mHHS >80 at the time of most recent follow-up. Perioperative variables, radiographic characteristics, and intraoperative findings were compared between the groups, in addition to a subgroup analysis based on sex. Results: The mean follow-up for successful hips was 30 months (SD, 11 months), with a mean mHHS of 95. In the failure group, 6 patients required subsequent procedures (4 anteverting periacetabular osteotomies and 2 total hip arthroplasties). The mean overall time to failure was 21 months, and the mean time to a second procedure was 24 months (total hip arthroplasty, 29.5 months; periacetabular osteotomy, 21.2 months); 18 hips failed on the basis of a low mHHS (mean, 65; range, 27-79) at last follow-up. Factors

Effect of Reinforcement Architecture on Fracture of Selectively Reinforced Metallic Compact Tension Specimens

NASA Technical Reports Server (NTRS)

Abada, Christopher H.; Farley, Gary L.; Hyer, Michael W.

2006-01-01

A computer-based parametric study of the effect of reinforcement architectures on fracture response of aluminum compact-tension (CT) specimens is performed. Eleven different reinforcement architectures consisting of rectangular and triangular cross-section reinforcements were evaluated. Reinforced specimens produced between 13 and 28 percent higher fracture load than achieved with the non-reinforced case. Reinforcements with blunt leading edges (rectangular reinforcements) exhibited superior performance relative to the triangular reinforcements with sharp leading edges. Relative to the rectangular reinforcements, the most important architectural feature was reinforcement thickness. At failure, the reinforcements carried between 58 and 85 percent of the load applied to the specimen, suggesting that there is considerable load transfer between the base material and the reinforcement.

Planetary rings as relics of plasma pre-rings

NASA Astrophysics Data System (ADS)

Rabinovich, B. I.

2007-02-01

A possibility is discussed that the rings of large planets observed in the modern epoch are relics of some pre-rings consisting of magnetized plasma (according to a hypothesis by H. Alfven). The solution to a model problem published in [36, 37] is used. Its main result is a mechanism of stratification of an evolutionally mature plasma pre-ring into a large number of narrow elite rings separated by anti-rings (gaps). Another result is the theoretical substantiation of the presence in the near-planetary space of a region of existence and stability (in what follows it is referred to as ES-region) of plasma rings. The data obtained in the course of the Voyager, Galileo, and Cassini missions are used below for verification of the model on which the solutions presented in [36, 37] are based.

Vibrations of a thin cylindrical shell stiffened by rings with various stiffness

NASA Astrophysics Data System (ADS)

Nesterchuk, G. A.

2018-05-01

The problem of vibrations of a thin-walled elastic cylindrical shell reinforced by frames of different rigidity is investigated. The solution for the case of the clamped shell edges was obtained by asymptotic methods and refined by the finite element method. Rings with zero eccentricity and stiffness varying along the generatrix of the shell cylinder are considered. Varying the optimal coefficients of the distribution functions of the rigidity of the frames and finding more precise parameters makes it possible to find correction factors for analytical formulas of approximate calculation.

Open-MRI measures of cam intrusion for hips in an anterior impingement position relate to acetabular contact force.

PubMed

Buchan, Lawrence L; Zhang, Honglin; Konan, Sujith; Heaslip, Ingrid; Ratzlaff, Charles R; Wilson, David R

2016-02-01

Open MRI in functional positions has potential to directly and non-invasively assess cam femoroacetabular impingement (FAI). Our objective was to investigate whether open MRI can depict intrusion of the cam deformity into the intra-articular joint space, and whether intrusion is associated with elevated acetabular contact force. Cadaver hips (9 cam; 3 controls) were positioned in an anterior impingement posture and imaged using open MRI with multi-planar reformatting. The β-angle (describing clearance between the femoral neck and acetabulum) was measured around the entire circumference of the femoral neck. We defined a binary "MRI cam-intrusion sign" (positive if β < 0°). We then instrumented each hip with a piezoresistive sensor and conducted six repeated positioning trials, measuring acetabular contact force (F). We defined a binary "contact-force sign" (positive if F > 20N). Cam hips were more likely than controls to have both a positive MRI cam-intrusion sign (p = 0.0182, Fisher's exact test) and positive contact-force sign (p = 0.0083), which represents direct experimental evidence for cam intrusion. There was also a relationship between the MRI cam-intrusion sign and contact-force sign (p = 0.033), representing a link between imaging and mechanics. Our findings indicate that open MRI has significant potential for in vivo investigation of the cam FAI mechanism. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Planetary Rings

NASA Astrophysics Data System (ADS)

Gordon, M. K.; Araki, S.; Black, G. J.; Bosh, A. S.; Brahic, A.; Brooks, S. M.; Charnoz, S.; Colwell, J. E.; Cuzzi, J. N.; Dones, L.; Durisen, R. H.; Esposito, L. W.; Ferrari, C.; Festou, M.; French, R. G.; Giuliatti-Winter, S. M.; Graps, A. L.; Hamilton, D. P.; Horanyi, M.; Karjalainen, R. M.; Krivov, A. V.; Krueger, H.; Larson, S. M.; Levison, H. F.; Lewis, M. C.; Lissauer, J. J.; Murray, C. D.; Namouni, F.; Nicholson, P. D.; Olkin, C. B.; Poulet, F.; Rappaport, N. J.; Salo, H. J.; Schmidt, J.; Showalter, M. R.; Spahn, F.; Spilker, L. J.; Srama, R.; Stewart, G. R.; Yanamandra-Fisher, P.

2002-08-01

The past two decades have witnessed dramatic changes in our view and understanding of planetary rings. We now know that each of the giant planets in the Solar System possesses a complex and unique ring system. Recent studies have identified complex gravitational interactions between the rings and their retinues of attendant satellites. Among the four known ring systems, we see elegant examples of Lindblad and corotation resonances (first invoked in the context of galactic disks), electromagnetic resonances, spiral density waves and bending waves, narrow ringlets which exhibit internal modes due to collective instabilities, sharp-edged gaps maintained via tidal torques from embedded moonlets, and tenuous dust belts created by meteoroid impact onto, or collisions between, parent bodies. Yet, as far as we have come, our understanding is far from complete. The fundamental questions confronting ring scientists at the beginning of the twenty-first century are those regarding the origin, age and evolution of the various ring systems, in the broadest context. Understanding the origin and age requires us to know the current ring properties, and to understand the dominant evolutionary processes and how they influence ring properties. Here we discuss a prioritized list of the key questions, the answers to which would provide the greatest improvement in our understanding of planetary rings. We then outline the initiatives, missions, and other supporting activities needed to address those questions, and recommend priorities for the coming decade in planetary ring science.

Evaluation of articular cartilage following rotational acetabular osteotomy for hip dysplasia using T2 mapping MRI.

PubMed

Shoji, Takeshi; Yamasaki, Takuma; Izumi, Soutaro; Sawa, Mikiya; Akiyama, Yuji; Yasunaga, Yuji; Adachi, Nobuo

2018-04-27

Rotational acetabular osteotomy (RAO) is one of the surgical treatments for acetabular dysplasia, and satisfactory results have been reported. We evaluated the postoperative changes of articular cartilage and whether the pre-operative condition of the articular cartilage influences the clinical results using T2 mapping MRI. We reviewed 31 hips with early stage osteoarthritis in 31 patients (mean age, 39.6 years), including three men and 28 women who underwent RAO for hip dysplasia. Clinical evaluations including Japanese Orthopedic Association (JOA) score and Japanese Orthopedic Association Hip Disease Evaluation Questionnaire (JHEQ), and radiographical evaluations on X-ray were performed. Longitudinal qualitative assessment of articular cartilage was also performed using 3.0-T MRI with T2 mapping technique preoperatively, 6 months, and at 1 and 2 years postoperatively. There was no case with progression of osteoarthritis. The mean JOA score improved from 70.1 to 93.4 points, the mean postoperative JHEQ score was 68.8 points, and radiographical data also improved postoperatively. We found that the T2 values of the cartilage at both femoral head and acetabulum increased at 6 months on coronal and sagittal views. However, they significantly decreased 1 and 2 years postoperatively. The T2 values of the center to anterolateral region of acetabulum negatively correlated with postoperative JHEQ score, particularly in pain score. This study suggests that biomechanical and anatomical changes could apparently cause decreased T2 values 1-2 years postoperatively compared with those preoperatively. Furthermore, preoperative T2 values of the acetabulum can be prognostic factors for the clinical results of RAO.

[Application of 3D printing and computer-assisted surgical simulation in preoperative planning for acetabular fracture].

PubMed

Liu, Xin; Zeng, Can-Jun; Lu, Jian-Sen; Lin, Xu-Chen; Huang, Hua-Jun; Tan, Xin-Yu; Cai, Dao-Zhang

2017-03-20

To evaluate the feasibility and effectiveness of using 3D printing and computer-assisted surgical simulation in preoperative planning for acetabular fractures. A retrospective analysis was performed in 53 patients with pelvic fracture, who underwent surgical treatment between September, 2013 and December, 2015 with complete follow-up data. Among them, 19 patients were treated with CT three-dimensional reconstruction, computer-assisted virtual reset internal fixation, 3D model printing, and personalized surgery simulation before surgery (3D group), and 34 patients underwent routine preoperative examination (conventional group). The intraoperative blood loss, transfusion volume, times of intraoperative X-ray, operation time, Matta score and Merle D' Aubigne & Postel score were recorded in the 2 groups. Preoperative planning and postoperative outcomes in the two groups were compared. All the operations were completed successfully. In 3D group, significantly less intraoperative blood loss, transfusion volume, fewer times of X-ray, and shortened operation time were recorded compared with those in the conventional group (P<0.05). According to the Matta scores, excellent or good fracture reduction was achieved in 94.7% (18/19) of the patients in 3D group and in 82.4% (28/34) of the patients in conventional group; the rates of excellent and good hip function at the final follow-up were 89.5% (17/19) in the 3D group and 85.3% (29/34) in the conventional group (P>0.05). In the 3D group, the actual internal fixation well matched the preoperative design. 3D printing and computer-assisted surgical simulation for preoperative planning is feasible and accurate for management of acetabular fracture and can effectively improve the operation efficiency.

The use of customized cages in revision total hip arthroplasty for Paprosky type III acetabular bone defects.

PubMed

Mao, Yuanqing; Xu, Chen; Xu, Jiawei; Li, Huiwu; Liu, Fengxiang; Yu, Degang; Zhu, Zhenan

2015-10-01

Revision total hip arthroplasty (THA) is challenging if severe periacetabular bone loss is present. Here we describe a method that uses a customised cage to reconstruct an acetabulum with a massive bone defect. Designed with the aid of the rapid prototyping technique, a customised cage with a hook, crest and flange or braids was made, and then utilized to reconstruct severe compromised acetabulum in revision THA since 2001. Twenty-two patients (23 hips) were included in this study. The mean patient age at the time of surgery was 60.9 years (range, 38-80 years). Three hips had massive acetabular bone defects of Paprosky type IIIA and 20 of type IIIB. The Harris hip score was used to evaluate hip function. Radiographs were taken to evaluate loosening of the cage and resorption of allograft bone. The average follow up was 81.6 ± 24.9 months. The mean Harris hip score improved from 39.6 pre-operatively to 80.9 at the final follow-up. There were no instances of deep infection, severe venous thrombosis, and nerve palsy. One patient who had an intra-operative rupture of the superior acetabular artery was successfully treated using the haemostatic suturing technique. Two patients experienced dislocation at post-operative days four and six, respectively, and both were treated with closed reduction and skin traction for three weeks. The present study demonstrates that a customised cage may be a promising option for THA revision of severely compromised acetabula. Extended follow-up is necessary to evaluate the long-term performance of this approach.

MODELING THE EFFECTS OF SENSORY REINFORCERS ON BEHAVIORAL PERSISTENCE WITH ALTERNATIVE REINFORCEMENT

PubMed Central

Sweeney, Mary M.; Moore, Keira; Shahan, Timothy A.; Ahearn, William H.; Dube, William V.; Nevin, John A.

2014-01-01

Problem behavior often has sensory consequences that cannot be separated from the target response, even if external, social reinforcers are removed during treatment. Because sensory reinforcers that accompany socially mediated problem behavior may contribute to persistence and relapse, research must develop analog sensory reinforcers that can be experimentally manipulated. In this research, we devised analogs to sensory reinforcers in order to control for their presence and determine how sensory reinforcers may impact treatment efficacy. Experiments 1 and 2 compared the efficacy of differential reinforcement of alternative behavior (DRA) versus noncontingent reinforcement (NCR) with and without analog sensory reinforcers in a multiple schedule. Experiment 1 measured the persistence of key pecking in pigeons, whereas Experiment 2 measured the persistence of touchscreen responses in children with intellectual and developmental disabilities. Across both experiments, the presence of analog sensory reinforcers increased the levels, persistence, and variability of responding relative to when analog sensory reinforcers were absent. Also in both experiments, target responding was less persistent under conditions of DRA compared to NCR regardless of the presence or absence of analog sensory reinforcers. PMID:25130416

Noncontingent reinforcement, alternative reinforcement, and the matching law: a laboratory demonstration.

PubMed Central

Ecott, Cheryl L; Critchfield, Thomas S

2004-01-01

Basic researchers, but not most applied researchers, have assumed that the behavior-decelerating effects of noncontingent reinforcement result at least partly from adventitious reinforcement of competing behaviors. The literature contains only sketchy evidence of these effects because few noncontingent reinforcement studies measure alternative behaviors. A laboratory model is presented in which concurrent schedules of contingent reinforcement were used to establish a "target" and an "alternative" behavior. Imposing noncontingent reinforcement decreased target behavior rates and increased alternative behavior rates, outcomes that were well described by the standard quantitative account of alternative reinforcement, the generalized matching law. These results suggest that adventitious reinforcement of alternative behaviors can occur during noncontingent reinforcement interventions, although the range of conditions under which this occurs remains to be determined in future studies. As an adjunct to applied studies, laboratory models permit easy measurement of alternative behaviors and parametric manipulations needed to answer many research questions. PMID:15529885

Reinforcement Magnitude: An Evaluation of Preference and Reinforcer Efficacy

ERIC Educational Resources Information Center

Trosclair-Lasserre, Nicole M.; Lerman, Dorothea C.; Call, Nathan A.; Addison, Laura R.; Kodak, Tiffany

2008-01-01

Consideration of reinforcer magnitude may be important for maximizing the efficacy of treatment for problem behavior. Nonetheless, relatively little is known about children's preferences for different magnitudes of social reinforcement or the extent to which preference is related to differences in reinforcer efficacy. The purpose of the current…

Autoshaping Chicks with Heat Reinforcement: The Role of Stimulus-Reinforcer and Response-Reinforcer Relations

ERIC Educational Resources Information Center

Wasserman, Edward A.; And Others

1975-01-01

The present series of experiments attempted to analyze more fully the contributions of stimulus-reinforcer and response-reinforcer relations to autoshaping within a single conditioning situation. (Author)

Saturn's Rings, the Yarkovsky Effects, and the Ring of Fire

NASA Technical Reports Server (NTRS)

Rubincam, David

2004-01-01

Saturn's icy ring particles, with their low thermal conductivity, are almost ideal for the operation of the Yarkovsky effects. The dimensions of Saturn's A and B rings may be determined by a near balancing of the seasonal Yarkovsky effect with the Yarkovsky- Schach effect. The two effects, which are photon thrust due to temperature gradients, may confine the A and B rings to within their observed dimensions. The C ring may be sparsely populated with icy particles because Yarkovsky drag has pulled them into Saturn, leaving the more slowly orbitally decaying rocky particles. Icy ring particles ejected from the B ring and passing through the C ring, as well as some of the slower rocky particles, should fall on Saturn's equator, where they may create a luminous "Ring of Fire" around Saturn's equator. This predicted Ring of Fire may be visible to Cassini's camera. Curiously, the speed of outwards Yarkovsky orbital evolution appears to peak near the Cassini Division. The connection between the two is not clear. D. Nesvorny has speculated that the resonance at the outer edge of the B ring may impede particles from evolving via Yarkovsky across the Division. If supply from the B ring is largely cut off, then Yarkovsky may push icy particles outward, away from the inner edge of the A ring, leaving only the rocky ones in the Division. The above scenarios depend delicately on the properties of the icy particles.

Variations in Ring Particle Cooling across Saturn's Rings with Cassini CIRS

NASA Astrophysics Data System (ADS)

Brooks, S. M.; Spilker, L. J.; Pilorz, S.; Edgington, S. G.; Déau, E.; Altobelli, N.

2010-12-01

Cassini's Composite Infrared Spectrometer has recorded over two million of spectra of Saturn's rings in the far infrared since arriving at Saturn in 2004. CIRS records far infrared radiation between 10 and 600 cm-1 ( 16.7 and 1000 μ {m} ) at focal plane 1 (FP1), which has a field of view of 3.9 mrad. Thermal emission from Saturn’s rings peaks in this wavelength range. Ring temperatures can be inferred from FP1 data. By tracking how ring temperatures vary, we can determine the thermal inertia of the rings. Previous studies have shown that the rings' thermal inertia, a measure of their response to changes in the thermal environment, varies from ring to ring. Thermal inertia can provide insight into the physical structure of Saturn's ring particles and their regoliths. Low thermal inertia and rapidly changing temperatures are suggestive of ring particles that have more porous or fluffy regoliths or that are riddled with cracks. Solid particles can be expected to have higher thermal inertias. Ferrari et al. (2005) fit thermal inertia values of 5218 {Jm)-2 {K}-1 {s}-1/2 to their B ring data and 6412 {Jm)-2 {K}-1 {s}-1/2 to their C ring data. In this work we focus on CIRS observations of the shadowed portion of Saturn's rings. The rings’ thermal budget is dominated by its absorption of solar radiation. As a result, ring particles abruptly cool as they traverse Saturn's shadow. From these shadow observations we can create cooling curves at specific locations across the rings. We will show that the rings' cooling curves and thus their thermal inertia vary not only from ring to ring, but by location within the individual rings. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2010 California Institute of Technology. Government sponsorship acknowledged.

Impact of Ring Current Ions on Electromagnetic Ion Cyclotron Wave Dispersion Relation

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Gamayunov, K. V.

2007-01-01

Effect of the ring current ions in the real part of electromagnetic ion Cyclotron wave dispersion relation is studied on global scale. Recent Cluster observations by Engebretson et al. showed that although the temperature anisotropy of is energetic (> 10 keV) ring current protons was high during the entire 22 November 2003 perigee pass, electromagnetic ion cyclotron waves were observed only in conjunction with intensification of the ion fluxes below 1 keV by over an order of magnitude. To study the effect of the ring current ions on the wave dispersive properties and the corresponding global wave redistribution, we use a self-consistent model of interacting ring current and electromagnetic ion cyclotron waves, and simulate the May 1998 storm. The main findings of our simulation can be summarized as follows: First, the plasma density enhancement in the night MLT sector during the main and recovery storm phases is mostly caused by injection of suprathermal plasma sheet H + (approximately < 1 keV), which dominate the thermal plasma density. Second, during the recovery storm phases, the ring current modification of the wave dispersion relation leads to a qualitative change of the wave patterns in the postmidnight-dawn sector for L > 4.75. This "new" wave activity is well organized by outward edges of dense suprathermal ring current spots, and the waves are not observed if the ring current ions are not included in the real part of dispersion relation. Third, the most intense wave-induced ring current precipitation is located in the night MLT sector and caused by modification of the wave dispersion relation. The strongest precipitating fluxes of about 8 X 10(exp 6)/ (cm(exp 2) - s X st) are found near L=5.75, MLT=2 during the early recovery phase on 4 May. Finally, the nightside precipitation is more intense than the dayside fluxes, even if there are less intense waves, because the convection field moves ring current ions into the loss cone on the nightside, but drives

Vortex rings

NASA Technical Reports Server (NTRS)

Shariff, Karim; Leonard, Anthony

1992-01-01

The vortex-ring problem in fluid mechanics is examined generally in terms of formation, the steady state, the duration of the rings, and vortex interactions. The formation is studied by examining the generation of laminar and turbulent vortex rings and their resulting structures with attention given to the three stages of laminar ring development. Inviscid dynamics is addressed to show how core dynamics affects overall ring motion, and laminar vortex structures are described in two dimensions. Viscous and inviscid structures are related in terms of 'leapfrogging', head-on collisions, and collisions with a no-slip wall. Linear instability theory is shown to successfully describe observational data, although late stages in the breakdown are not completely understood. This study of vortex rings has important implications for key aerodynamic issues including sound generation, transport and mixing, and vortex interactions.

Asymmetric dipolar ring

DOEpatents

Prosandeev, Sergey A.; Ponomareva, Inna V.; Kornev, Igor A.; Bellaiche, Laurent M.

2010-11-16

A device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field.

Concentric ring flywheel with hooked ring carbon fiber separator/torque coupler

DOEpatents

Kuklo, Thomas C.

1999-01-01

A concentric ring flywheel with expandable separators, which function as torque couplers, between the rings to take up the gap formed between adjacent rings due to differential expansion between different radius rings during rotation of the flywheel. The expandable separators or torque couplers include a hook-like section at an upper end which is positioned over an inner ring and a shelf-like or flange section at a lower end onto which the next adjacent outer ring is positioned. As the concentric rings are rotated the gap formed by the differential expansion there between is partially taken up by the expandable separators or torque couplers to maintain torque and centering attachment of the concentric rings.

Concentric ring flywheel with hooked ring carbon fiber separator/torque coupler

DOEpatents

Kuklo, T.C.

1999-07-20

A concentric ring flywheel with expandable separators, which function as torque couplers, between the rings to take up the gap formed between adjacent rings due to differential expansion between different radius rings during rotation of the flywheel. The expandable separators or torque couplers include a hook-like section at an upper end which is positioned over an inner ring and a shelf-like or flange section at a lower end onto which the next adjacent outer ring is positioned. As the concentric rings are rotated the gap formed by the differential expansion there between is partially taken up by the expandable separators or torque couplers to maintain torque and centering attachment of the concentric rings. 2 figs.

Low Frequency of Early Complications With Dual-mobility Acetabular Cups in Cementless Primary THA.

PubMed

Chughtai, Morad; Mistry, Jaydev B; Diedrich, Aloise M; Jauregui, Julio J; Elmallah, Randa K; Bonutti, Peter M; Harwin, Steven F; Malkani, Arthur L; Kolisek, Frank R; Mont, Michael A

2016-10-01

Dislocation complicates 1% to 5% of primary total hip arthroplasties (THAs). As a result, some surgeons consider dual-mobility articulations, which are usually used in the revision setting to decrease the likelihood of dislocation, as an option for primary THA. However, few studies have evaluated their use in this setting. (1) What is the cup survivorship when the dual-mobility articulation is used in the setting of primary THA? (2) What are the clinical outcomes with this approach? (3) What are the radiographic outcomes? (4) What are the complications of dual-mobility articulations in primary THA? Between 2011 and 2013, the five participating surgeons performed 495 cementless primary THAs. During that time, one of the five surgeons used dual-mobility articulations for all THAs, and the other four used it whenever the acetabular cup size was 52 mm or greater to enable a 28-mm head. Of the 495 patients, 453 (92%) were performed using this device. Smaller patients were treated with a standard THA. Of the 453 patients, a total of 43 patients (10%) were lost to followup before the 2-year minimum. The resulting 410 patients who were included in the analysis (164 men, 246 women) had a mean age of 64 years (SD, 12 years). The mean followup was 3 years (SD, 0.7 years). We performed Kaplan-Meier analyses to assess survivorship to aseptic failure and all-cause acetabular component survivorship. Clinical outcomes were evaluated using the Harris hip score (HHS); radiographs were assessed for cup migration, progressive radiolucencies, and positional changes of the components; and any surgery-related complications were recorded. The survivorship to aseptic failure and all-cause acetabular component survivorship was 99.8% (failures, n = 1) (95% confidence interval [CI], 4.517-4.547) and 99.3% (failures, aseptic, n = 1; septic, n = 2) (95% CI, 4.494-4.543); one hip had trunnion notching caused by impingement of a malpositioned cup, which was treated with revision of the cup and

Structural Behavior of Concrete Beams Reinforced with Basalt Fiber Reinforced Polymer (BFRP) Bars

NASA Astrophysics Data System (ADS)

Ovitigala, Thilan

The main challenge for civil engineers is to provide sustainable, environmentally friendly and financially feasible structures to the society. Finding new materials such as fiber reinforced polymer (FRP) material that can fulfill the above requirements is a must. FRP material was expensive and it was limited to niche markets such as space shuttles and air industry in the 1960s. Over the time, it became cheaper and spread to other industries such as sporting goods in the 1980-1990, and then towards the infrastructure industry. Design and construction guidelines are available for carbon fiber reinforced polymer (CFRP), aramid fiber reinforced polymer (AFRP) and glass fiber reinforced polymer (GFRP) and they are currently used in structural applications. Since FRP is linear elastic brittle material, design guidelines for the steel reinforcement are not valid for FRP materials. Corrosion of steel reinforcement affects the durability of the concrete structures. FRP reinforcement is identified as an alternative to steel reinforcement in corrosive environments. Although basalt fiber reinforced polymer (BFRP) has many advantages over other FRP materials, but limited studies have been done. These studies didn't include larger BFRP bar diameters that are mostly used in practice. Therefore, larger beam sizes with larger BFRP reinforcement bar diameters are needed to investigate the flexural and shear behavior of BFRP reinforced concrete beams. Also, shear behavior of BFRP reinforced concrete beams was not yet studied. Experimental testing of mechanical properties and bond strength of BFRP bars and flexural and shear behavior of BFRP reinforced concrete beams are needed to include BFRP reinforcement bars in the design codes. This study mainly focuses on the use of BFRP bars as internal reinforcement. The test results of the mechanical properties of BFRP reinforcement bars, the bond strength of BFRP reinforcement bars, and the flexural and shear behavior of concrete beams

Intraoperative assessment of reduction and implant placement in acetabular fractures-limitations of 3D-imaging compared to computed tomography.

PubMed

Keil, Holger; Beisemann, Nils; Schnetzke, Marc; Vetter, Sven Yves; Swartman, Benedict; Grützner, Paul Alfred; Franke, Jochen

2018-04-10

In acetabular fractures, the assessment of reduction and implant placement has limitations in conventional 2D intraoperative imaging. 3D imaging offers the opportunity to acquire CT-like images and thus to improve the results. However, clinical experience shows that even 3D imaging has limitations, especially regarding artifacts when implants are placed. The purpose of this study was to assess the difference between intraoperative 3D imaging and postoperative CT regarding reduction and implant placement. Twenty consecutive cases of acetabular fractures were selected with a complete set of intraoperative 3D imaging and postoperative CT data. The largest detectable step and the largest detectable gap were measured in all three standard planes. These values were compared between the 3D data sets and CT data sets. Additionally, possible correlations between the possible confounders age and BMI and the difference between 3D and CT values were tested. The mean difference of largest visible step between the 3D imaging and CT scan was 2.0 ± 1.8 mm (0.0-5.8, p = 0.02) in the axial, 1.3 ± 1.4 mm (0.0-3.7, p = 0.15) in the sagittal and 1.9 ± 2.4 mm (0.0-7.4, p = 0.22) in the coronal views. The mean difference of largest visible gap between the 3D imaging and CT scan was 3.1 ± 3.6 mm (0.0-14.1, p = 0.03) in the axial, 4.6 ± 2.7 mm (1.2-8.7, p = 0.001) in the sagittal and 3.5 ± 4.0 mm (0.0-15.4, p = 0.06) in the coronal views. A positive correlation between the age and the difference in gap measurements in the sagittal view was shown (rho = 0.556, p = 0.011). Intraoperative 3D imaging is a valuable adjunct in assessing reduction and implant placement in acetabular fractures but has limitations due to artifacts caused by implant material. This can lead to missed malreduction and impairment of clinical outcome, so postoperative CT should be considered in these cases.

Comparison of Three-Dimensional Planning-Assisted and Conventional Acetabular Cup Positioning in Total Hip Arthroplasty: A Randomized Controlled Trial.

PubMed

Sariali, Elhadi; Boukhelifa, Nadia; Catonne, Yves; Pascal Moussellard, Hugues

2016-01-20

Malpositioning of the acetabular cup during total hip arthroplasty increases the risk of dislocation, edge-loading, squeaking, early wear, and loosening. We hypothesized that the use of three-dimensional (3-D) visualization tools to identify the planned cup position relative to the acetabular edge intraoperatively would increase the accuracy of cup orientation. The purpose of this study was to compare 3-D planning-assisted implantation and freehand insertion of the acetabular cup. This was a prospective randomized controlled study of two groups of twenty-eight patients each. In the first group, cup positioning was guided by 3-D views of the cup within the acetabulum obtained during 3-D preoperative planning. In the control group, the cup was placed freehand. All of the patients were operated on by the same surgeon, through a minimally invasive direct anterior approach with the patient in the supine position. Cup anteversion and abduction angles were measured on 3-D computed tomography (CT) reconstructions. The main evaluation criterion was the percentage of outliers according to the Lewinnek safe zone. Operative time did not differ between the two groups. The cup anteversion was more accurate in the 3-D planning group (mean difference from the planned angle [and standard deviation], -2.7° ± 5.4°) compared with the freehand-placement group (6.6° ± 9.5°). According to the Lewinnek safe zone, overall, the percentage of outliers was lower in the 3-D planning group (21%; six patients) than in the control group (46%; thirteen patients). According to the Callanan safe zone, the percentage of outliers was also lower in the 3-D planning group (25% versus 64%). Although cup abduction was also restored with greater accuracy in the 3-D planning group, on the basis of the Lewinnek safe zone, the percentage of abduction outliers was comparable between groups, with fewer high-abduction values, but more low-abduction values, in the 3-D planning group. Preoperative 3-D

Saturn's Rings, the Yarkovsky Effects, and the Ring of Fire

NASA Technical Reports Server (NTRS)

Rubincam, David Parry

2004-01-01

The dimensions of Saturn's A and B rings may be determined by the seasonal Yarkovsky effect and the Yarkovsky-Schach effect; the two effects confine the rings between approximately 1.68 and approximately 2.23 Saturn radii, in reasonable agreement with the observed values of 1.525 and 2.267. The C ring may be sparsely populated because its particles are transients on their way to Saturn; the infall may create a luminous Ring of Fire around Saturn's equator. The ring system may be young: in the past heat flow from Saturn's interior much above its present value would not permit rings to exist.

Saturn's largest ring.

PubMed

Verbiscer, Anne J; Skrutskie, Michael F; Hamilton, Douglas P

2009-10-22

Most planetary rings in the Solar System lie within a few radii of their host body, because at these distances gravitational accelerations inhibit satellite formation. The best known exceptions are Jupiter's gossamer rings and Saturn's E ring, broad sheets of dust that extend outward until they fade from view at five to ten planetary radii. Source satellites continuously supply the dust, which is subsequently lost in collisions or by radial transport. Here we report that Saturn has an enormous ring associated with its outer moon Phoebe, extending from at least 128R(S) to 207R(S) (Saturn's radius R(S) is 60,330 km). The ring's vertical thickness of 40R(S) matches the range of vertical motion of Phoebe along its orbit. Dynamical considerations argue that these ring particles span the Saturnian system from the main rings to the edges of interplanetary space. The ring's normal optical depth of approximately 2 x 10(-8) is comparable to that of Jupiter's faintest gossamer ring, although its particle number density is several hundred times smaller. Repeated impacts on Phoebe, from both interplanetary and circumplanetary particle populations, probably keep the ring populated with material. Ring particles smaller than centimetres in size slowly migrate inward and many of them ultimately strike the dark leading face of Iapetus.

Slowing down of ring polymer diffusion caused by inter-ring threading.

PubMed

Lee, Eunsang; Kim, Soree; Jung, YounJoon

2015-06-01

Diffusion of long ring polymers in a melt is much slower than the reorganization of their internal structures. While direct evidence for entanglements has not been observed in the long ring polymers unlike linear polymer melts, threading between the rings is suspected to be the main reason for slowing down of ring polymer diffusion. It is, however, difficult to define the threading configuration between two rings because the rings have no chain end. In this work, evidence for threading dynamics of ring polymers is presented by using molecular dynamics simulation and applying a novel analysis method. The simulation results are analyzed in terms of the statistics of persistence and exchange times that have proved useful in studying heterogeneous dynamics of glassy systems. It is found that the threading time of ring polymer melts increases more rapidly with the degree of polymerization than that of linear polymer melts. This indicates that threaded ring polymers cannot diffuse until an unthreading event occurs, which results in the slowing down of ring polymer diffusion. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Adapting without reinforcement.

PubMed

Kheifets, Aaron; Gallistel, C Randy

2012-11-01

Our data rule out a broad class of behavioral models in which behavioral change is guided by differential reinforcement. To demonstrate this, we showed that the number of reinforcers missed before the subject shifted its behavior was not sufficient to drive behavioral change. What's more, many subjects shifted their behavior to a more optimal strategy even when they had not yet missed a single reinforcer. Naturally, differential reinforcement cannot be said to drive a process that shifts to accommodate to new conditions so adeptly that it doesn't miss a single reinforcer: it would have no input on which to base this shift.

Assessment of Accuracy and Reliability in Acetabular Cup Placement Using an iPhone/iPad System.

PubMed

Kurosaka, Kenji; Fukunishi, Shigeo; Fukui, Tomokazu; Nishio, Shoji; Fujihara, Yuki; Okahisa, Shohei; Takeda, Yu; Daimon, Takashi; Yoshiya, Shinichi

2016-07-01

Implant positioning is one of the critical factors that influences postoperative outcome of total hip arthroplasty (THA). Malpositioning of the implant may lead to an increased risk of postoperative complications such as prosthetic impingement, dislocation, restricted range of motion, polyethylene wear, and loosening. In 2012, the intraoperative use of smartphone technology in THA for improved accuracy of acetabular cup placement was reported. The purpose of this study was to examine the accuracy of an iPhone/iPad-guided technique in positioning the acetabular cup in THA compared with the reference values obtained from the image-free navigation system in a cadaveric experiment. Five hips of 5 embalmed whole-body cadavers were used in the study. Seven orthopedic surgeons (4 residents and 3 senior hip surgeons) participated in the study. All of the surgeons examined each of the 5 hips 3 times. The target angle was 38°/19° for operative inclination/anteversion angles, which corresponded to radiographic inclination/anteversion angles of 40°/15°. The simultaneous assessment using the navigation system showed mean±SD radiographic alignment angles of 39.4°±2.6° and 16.4°±2.6° for inclination and anteversion, respectively. Assessment of cup positioning based on Lewinnek's safe zone criteria showed all of the procedures (n=105) achieved acceptable alignment within the safe zone. A comparison of the performances by resident and senior hip surgeons showed no significant difference between the groups (P=.74 for inclination and P=.81 for anteversion). The iPhone/iPad technique examined in this study could achieve acceptable performance in determining cup alignment in THA regardless of the surgeon's expertise. [Orthopedics. 2016; 39(4):e621-e626.]. Copyright 2016, SLACK Incorporated.

Investigations of timing during the schedule and reinforcement intervals with wheel-running reinforcement.

PubMed

Belke, Terry W; Christie-Fougere, Melissa M

2006-11-01

Across two experiments, a peak procedure was used to assess the timing of the onset and offset of an opportunity to run as a reinforcer. The first experiment investigated the effect of reinforcer duration on temporal discrimination of the onset of the reinforcement interval. Three male Wistar rats were exposed to fixed-interval (FI) 30-s schedules of wheel-running reinforcement and the duration of the opportunity to run was varied across values of 15, 30, and 60s. Each session consisted of 50 reinforcers and 10 probe trials. Results showed that as reinforcer duration increased, the percentage of postreinforcement pauses longer than the 30-s schedule interval increased. On probe trials, peak response rates occurred near the time of reinforcer delivery and peak times varied with reinforcer duration. In a second experiment, seven female Long-Evans rats were exposed to FI 30-s schedules leading to 30-s opportunities to run. Timing of the onset and offset of the reinforcement period was assessed by probe trials during the schedule interval and during the reinforcement interval in separate conditions. The results provided evidence of timing of the onset, but not the offset of the wheel-running reinforcement period. Further research is required to assess if timing occurs during a wheel-running reinforcement period.

Uranus Tenth Ring

NASA Image and Video Library

1996-01-29

On Jan. 23, 1986, NASA Voyager 2 discovered a tenth ring orbiting Uranus. The tenth ring is about midway between the bright, outermost epsilon ring and the next ring down, called delta. http://photojournal.jpl.nasa.gov/catalog/PIA00035

Jupiter Ring Halo

NASA Image and Video Library

1998-03-26

A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (km) per picture element (pixel) along the rings; however, because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow peering back toward the Sun; the ring was approximately 2,300,000 kilometers (km) away. The arc on the far right of the image is produced by sunlight scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age. Jupiter's ring system is composed of three parts -- a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, which lies exterior to the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the far left side of the figure. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow. A faint mist of particles can be seen above and below the main rings; this vertically extended, toroidal "halo" is unusual in planetary rings, and is probably caused by electromagnetic forces which can push small grains out of the ring plane. Halo material is present across this entire image, implying that it reaches more than 27,000 km above the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. In order to accentuate faint features in the image, different brightnesses are shown through color, with the brightest being

Birth Control Ring

MedlinePlus

... Safe Videos for Educators Search English Español Birth Control Ring KidsHealth / For Teens / Birth Control Ring What's in this article? What Is It? ... Anillo vaginal anticonceptivo What Is It? The birth control ring is a soft, flexible, doughnut-shaped ring ...

Evaluating the Influence of Postsession Reinforcement on Choice of Reinforcers

ERIC Educational Resources Information Center

Kodak, Tiffany; Lerman, Dorothea C.; Call, Nathan

2007-01-01

Factors that influence reinforcer choice have been examined in a number of applied studies (e.g., Neef, Mace, Shea, & Shade, 1992; Shore, Iwata, DeLeon, Kahng, & Smith, 1997; Tustin, 1994). However, no applied studies have evaluated the effects of postsession reinforcement on choice between concurrently available reinforcers, even though basic…

Adapting without reinforcement

PubMed Central

Kheifets, Aaron; Gallistel, C. Randy

2012-01-01

Our data rule out a broad class of behavioral models in which behavioral change is guided by differential reinforcement. To demonstrate this, we showed that the number of reinforcers missed before the subject shifted its behavior was not sufficient to drive behavioral change. What’s more, many subjects shifted their behavior to a more optimal strategy even when they had not yet missed a single reinforcer. Naturally, differential reinforcement cannot be said to drive a process that shifts to accommodate to new conditions so adeptly that it doesn’t miss a single reinforcer: it would have no input on which to base this shift. PMID:23336018

A simple method of measuring the wear of explanted acetabular component inserts

PubMed Central

Krakow, L.; Klockow, A.; Roehner, E.; Brodt, S.; Eijer, H.; Bossert, J.

2017-01-01

Objectives The determination of the volumetric polyethylene wear on explanted material requires complicated equipment, which is not available in many research institutions. Our aim in this study was to present and validate a method that only requires a set of polyetheretherketone balls and a laboratory balance to determine wear. Methods The insert to be measured was placed on a balance, and a ball of the appropriate diameter was inserted. The cavity remaining between the ball and insert caused by wear was filled with contrast medium and the weight of the contrast medium was recorded. The volume was calculated from the known density of the liquid. The precision, inter- and intraobserver reliability, were determined by four investigators on four days using nine inserts with specified wear (0.094 ml to 1.626 ml), and the intra-class correlation coefficient was calculated. The feasibility of using this method in routine clinical practice and the time required for measurement were tested on 84 explanted inserts by one investigator. Results In order to get the mean for all investigators and determinations, the deviation between the measured and specified wear was -0.08 ml (sd 0.12; -0.21 to 0.11). The interobserver reliability was 0.989 ml (95% confidence interval (CI) 0.964 to 0.997) and the intraobserver reliability was 0.941 for observer 1 (95% CI 0.846 to 0.985), 0.983 for observer 2 (95% CI 0.956 to 0.995), 0.939 for observer 3 (95% CI 0.855 to 0.984), and 0.934 for observer 4 (95% CI 0.790 to 0.984). The mean time required to examine the samples was two minutes (sd 2; 1 to 5). Conclusion The method presented here was shown to be sufficiently precise for many settings and is a cost-effective and quick method of determining the volumetric wear of explanted acetabular components. However, the measurement of wear for scientific purposes will probably continue to involve more accurate and dedicated laboratory equipment. Cite this article: L. Krakow, A. Klockow, E

Planetary Rings

NASA Technical Reports Server (NTRS)

Cuzzi, Jeffrey N.

1994-01-01

Just over two decades ago, Jim Pollack made a critical contribution to our understanding of planetary ring particle properties, and resolved a major apparent paradox between radar reflection and radio emission observations. At the time, particle properties were about all there were to study about planetary rings, and the fundamental questions were, why is Saturn the only planet with rings, how big are the particles, and what are they made of? Since then, we have received an avalanche of observations of planetary ring systems, both from spacecraft and from Earth. Meanwhile, we have seen steady progress in our understanding of the myriad ways in which gravity, fluid and statistical mechanics, and electromagnetism can combine to shape the distribution of the submicron-to-several-meter size particles which comprise ring systems into the complex webs of structure that we now know them to display. Insights gained from studies of these giant dynamical analogs have carried over into improved understanding of the formation of the planets themselves from particle disks, a subject very close to Jim's heart. The now-complete reconnaissance of the gas giant planets by spacecraft has revealed that ring systems are invariably found in association with families of regular satellites, and there is ark emerging perspective that they are not only physically but causally linked. There is also mounting evidence that many features or aspects of all planetary ring systems, if not the ring systems themselves, are considerably younger than the solar system

The Saturn Ring Observer: In situ studies of planetary rings

NASA Astrophysics Data System (ADS)

Nicholson, P. D.; Tiscareno, M. S.; Spilker, L. J.

2010-12-01

As part of the Planetary Science Decadal Survey recently undertaken by the NRC's Space Studies Board for the National Academy of Sciences, studies were commissioned for a number of potential missions to outer planet targets. One of these studies examined the technological feasibility of a mission to carry out in situ studies of Saturn's rings, from a spacecraft placed in a circular orbit above the ring plane: the Saturn Ring Observer. The technical findings and background are discussed in a companion poster by T. R. Spilker et al. Here we outline the science goals of such a mission. Most of the fundamental interactions in planetary rings occur on spatial scales that are unresolved by flyby or orbiter spacecraft. Typical particle sizes in the rings of Saturn are in the 1 cm - 10 m range, and average interparticle spacings are a few meters. Indirect evidence indicates that the vertical thickness of the rings is as little as 5 - 10 m, which implies a velocity dispersion of only a few mm/sec. Theories of ring structure and evolution depend on the unknown characteristics of interparticle collisions and on the size distribution of the ring particles. The SRO could provide direct measurements of both the coefficient of restitution -- by monitoring individual collisions -- and the particles’ velocity dispersion. High-resolution observations of individual ring particles should also permit estimates of their spin states. Numerical simulations of Saturn’s rings incorporating both collisions and self-gravity predict that the ring particles are not uniformly distributed, but are instead clustered into elongated structures referred to as “self-gravity wakes”, which are continually created and destroyed on an orbital timescale. Theory indicates that the average separation between wakes in the A ring is of order 30-100 m. Direct imaging of self-gravity wakes, including their formation and subsequent dissolution, would provide critical validation of these models. Other

Prestressed Ring Beam in the Church of St. Peter’s and Paul’s in Bodzanow, Design and Realization

NASA Astrophysics Data System (ADS)

Szydlowski, Rafal; Labuzek, Barbara; Turcza, Monika

2017-10-01

The present trend in architecture is designing thin. slender and spacious architectural forms. It has become the reason for searching for new solutions and finding new ways of use of the existing construction ones. Recently, the first time in Poland, the post-tensioning has been used in realization of church building. In the Church of St. Peter’s and Paul’s in Bodzanow (near Cracow) was designed circumferential ring beam post-tensioned with 4 unbounded tendons to transfer peripheral tensile forces from the roof. Thanks to the use of a prestressed ring beam hidden in the wall, large cross-section of roof girders was possible to be avoided, as well as a massive reinforced concrete ring or additional steel tie-rods. The paper presents the applied solutions in details with the theoretical calculated results as well as the results of prestressing measured in site during tensioning of tendons. Based on presented results some conclusions have been drawn.

Jupiter's Main Ring

NASA Technical Reports Server (NTRS)

1997-01-01

A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (km) per picture element (pixel) along the rings; however, because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow peering back toward the Sun; the ring was approximately 2,300,000 kilometers (km) away. The arc on the far right of the image is produced by sunlight scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age.

Jupiter's ring system is composed of three parts -- a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, which lies exterior to the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the far left side of the figure. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow. Some radial structure is barely visible across the ring's ansa. A faint mist of particles can be seen above and below the main rings; this vertically extended 'halo' is unusual in planetary rings, and is probably caused by electromagnetic forces pushing the smallest grains out of the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic.

Jupiter's main ring is a thin strand of material encircling the planet. The diffuse innermost boundary begins at approximately 123,000 km. The main ring's outer radius is found to be

Food reinforcement during infancy

PubMed Central

Kong, Kai Ling

2017-01-01

The motivation to eat, as operationalized by measuring how hard someone will work for food, is cross-sectionally and prospectively related to obesity. Persons high in food reinforcement consume more calories, and energy intake mediates the relationship between food reinforcement and obesity. Research has shown avid sucking for milk in early infancy predicts later adiposity, and the relationship between food reinforcement and excess body weight has been observed in infants as young as 9 months of age. New methodological developments in studying food reinforcement in infants and young children provide the first opportunity to study the origin of food reinforcement. This review seeks to provide background on the measurement of food reinforcement, and to present, for the first time, prenatal and postnatal predictors of infant food reinforcement. Lastly, potential mechanisms for an increasing trajectory of food reinforcement throughout development are proposed. PMID:27373207

Positive effect of removal of subchondral bone plate for cemented acetabular component fixation in total hip arthroplasty: a randomised RSA study with ten-year follow-up.

PubMed

Flivik, G; Kristiansson, I; Ryd, L

2015-01-01

We hypothesised that the removal of the subchondral bone plate (SCBP) for cemented acetabular component fixation in total hip arthroplasty (THA) offers advantages over retention by improving the cement-bone interface, without jeopardising implant stability. We have previously published two-year follow-up data of a randomised controlled trial (RCT), in which 50 patients with primary osteoarthritis were randomised to either retention or removal of the SCBP. The mean age of the retention group (n = 25, 13 males) was 70.0 years (sd 6.8). The mean age in the removal group (n = 25, 16 males) was 70.3 years (sd 7.9). Now we have followed up the patients at six (retention group, n = 21; removal group, n = 20) and ten years (retention group: n = 17, removal group: n = 18), administering clinical outcome questionnaires and radiostereometric analysis (RSA), and determining the presence of radiolucent lines (RLLs) on conventional radiographs. RSA demonstrated similar translation and rotation patterns up to six years. Between six and ten years, proximal acetabular component migration and changes of inclination were larger in the retention group, although the mean differences did not reach statistical significance. Differences in migration were driven by two patients in the SCBP retention group with extensive migration versus none in the SCBP removal group. The significant difference (p < 0.001) in the development of radiolucent lines in the retention group, previously observed at two years, increased even further during the course of follow-up (p < 0.001). While recognising SCBP removal is a more demanding technique, we conclude that, wherever possible, the SCBP should be removed to improve the cement-bone interface in order to maximise acetabular component stability and longevity. ©2015 The British Editorial Society of Bone & Joint Surgery.

A Wireless Passive Sensing System for Displacement/Strain Measurement in Reinforced Concrete Members

PubMed Central

Ozbey, Burak; Erturk, Vakur B.; Demir, Hilmi Volkan; Altintas, Ayhan; Kurc, Ozgur

2016-01-01

In this study, we show a wireless passive sensing system embedded in a reinforced concrete member successfully being employed for the measurement of relative displacement and strain in a simply supported beam experiment. The system utilizes electromagnetic coupling between the transceiver antenna located outside the beam, and the sensing probes placed on the reinforcing bar (rebar) surface inside the beam. The probes were designed in the form of a nested split-ring resonator, a metamaterial-based structure chosen for its compact size and high sensitivity/resolution, which is at µm/microstrains level. Experiments were performed in both the elastic and plastic deformation cases of steel rebars, and the sensing system was demonstrated to acquire telemetric data in both cases. The wireless measurement results from multiple probes are compared with the data obtained from the strain gages, and an excellent agreement is observed. A discrete time measurement where the system records data at different force levels is also shown. Practical issues regarding the placement of the sensors and accurate recording of data are discussed. The proposed sensing technology is demonstrated to be a good candidate for wireless structural health monitoring (SHM) of reinforced concrete members by its high sensitivity and wide dynamic range. PMID:27070615

Habituation of reinforcer effectiveness

PubMed Central

Lloyd, David R.; Medina, Douglas J.; Hawk, Larry W.; Fosco, Whitney D.; Richards, Jerry B.

2014-01-01

In this paper we propose an integrative model of habituation of reinforcer effectiveness (HRE) that links behavioral- and neural-based explanations of reinforcement. We argue that HRE is a fundamental property of reinforcing stimuli. Most reinforcement models implicitly suggest that the effectiveness of a reinforcer is stable across repeated presentations. In contrast, an HRE approach predicts decreased effectiveness due to repeated presentation. We argue that repeated presentation of reinforcing stimuli decreases their effectiveness and that these decreases are described by the behavioral characteristics of habituation (McSweeney and Murphy, 2009; Rankin etal., 2009). We describe a neural model that postulates a positive association between dopamine neurotransmission and HRE. We present evidence that stimulant drugs, which artificially increase dopamine neurotransmission, disrupt (slow) normally occurring HRE and also provide evidence that stimulant drugs have differential effects on operant responding maintained by reinforcers with rapid vs. slow HRE rates. We hypothesize that abnormal HRE due to genetic and/or environmental factors may underlie some behavioral disorders. For example, recent research indicates that slow-HRE is predictive of obesity. In contrast ADHD may reflect “accelerated-HRE.” Consideration of HRE is important for the development of effective reinforcement-based treatments. Finally, we point out that most of the reinforcing stimuli that regulate daily behavior are non-consumable environmental/social reinforcers which have rapid-HRE. The almost exclusive use of consumable reinforcers with slow-HRE in pre-clinical studies with animals may have caused the importance of HRE to be overlooked. Further study of reinforcing stimuli with rapid-HRE is needed in order to understand how habituation and reinforcement interact and regulate behavior. PMID:24409128

Habituation of reinforcer effectiveness.

PubMed

Lloyd, David R; Medina, Douglas J; Hawk, Larry W; Fosco, Whitney D; Richards, Jerry B

2014-01-09

In this paper we propose an integrative model of habituation of reinforcer effectiveness (HRE) that links behavioral- and neural-based explanations of reinforcement. We argue that HRE is a fundamental property of reinforcing stimuli. Most reinforcement models implicitly suggest that the effectiveness of a reinforcer is stable across repeated presentations. In contrast, an HRE approach predicts decreased effectiveness due to repeated presentation. We argue that repeated presentation of reinforcing stimuli decreases their effectiveness and that these decreases are described by the behavioral characteristics of habituation (McSweeney and Murphy, 2009; Rankin etal., 2009). We describe a neural model that postulates a positive association between dopamine neurotransmission and HRE. We present evidence that stimulant drugs, which artificially increase dopamine neurotransmission, disrupt (slow) normally occurring HRE and also provide evidence that stimulant drugs have differential effects on operant responding maintained by reinforcers with rapid vs. slow HRE rates. We hypothesize that abnormal HRE due to genetic and/or environmental factors may underlie some behavioral disorders. For example, recent research indicates that slow-HRE is predictive of obesity. In contrast ADHD may reflect "accelerated-HRE." Consideration of HRE is important for the development of effective reinforcement-based treatments. Finally, we point out that most of the reinforcing stimuli that regulate daily behavior are non-consumable environmental/social reinforcers which have rapid-HRE. The almost exclusive use of consumable reinforcers with slow-HRE in pre-clinical studies with animals may have caused the importance of HRE to be overlooked. Further study of reinforcing stimuli with rapid-HRE is needed in order to understand how habituation and reinforcement interact and regulate behavior.

Composite intersection reinforcement

NASA Technical Reports Server (NTRS)

Misciagna, David T. (Inventor); Fuhrer, Jessica J. (Inventor); Funk, Robert S. (Inventor); Tolotta, William S. (Inventor)

2010-01-01

An assembly and method for manufacturing a composite reinforcement for unitizing a structure are provided. According to one embodiment, the assembly includes a base having a plurality of pins extending outwardly therefrom to define a structure about which a composite fiber is wound to define a composite reinforcement preform. The assembly also includes a plurality of mandrels positioned adjacent to the base and at least a portion of the composite reinforcement preform, and a cap that is positioned over at least a portion of the plurality of mandrels. The cap is configured to engage each of the mandrels to support the mandrels and the composite reinforcement preform during a curing process to form the composite reinforcement.

Composite Intersection Reinforcement

NASA Technical Reports Server (NTRS)

Misciagna, David T. (Inventor); Fuhrer, Jessica J. (Inventor); Funk, Robert S. (Inventor); Tolotta, William S. (Inventor)

2013-01-01

An assembly and method for manufacturing a composite reinforcement for unitizing a structure are provided. According to one embodiment, the assembly includes a base having a plurality of pins extending outwardly therefrom to define a structure about which a composite fiber is wound to define a composite reinforcement preform. The assembly also includes a plurality of mandrels positioned adjacent to the base and at least a portion of the composite reinforcement preform, and a cap that is positioned over at least a portion of the plurality of mandrels. The cap is configured to engage each of the mandrels to support the mandrels and the composite reinforcement preform during a curing process to form the composite reinforcement.

Jupiter's ring

NASA Technical Reports Server (NTRS)

1979-01-01

First evidence of a ring around the planet Jupiter is seen in this photograph taken by Voyager 1 on March 4, 1979. The multiple exposure of the extremely thin faint ring appears as a broad light band crossing the center of the picture. The edge of the ring is 1,212,000 km from the spacecraft and 57,000 km from the visible cloud deck of Jupiter. The background stars look like broken hair pins because of spacecraft motion during the 11 minute 12 second exposure. The wavy motion of the star trails is due to the ultra-slow natural oscillation of the spacecraft (with a period of 78 seconds). The black dots are geometric calibration points in the camera. The ring thickness is estimated to be 30 km or less. The photograph was part of a sequence planned to search for such rings in Jupiter's equatorial plane. The ring has been invisible from Earth because of its thinness and its transparency when viewed at any angle except straight on. JPL manages and controls the Voyager Project for NASA's Office of Space Science.

Composite Reinforcement by Magnetic Control of Fiber Density and Orientation.

PubMed

Goldberg, Omri; Greenfeld, Israel; Wagner, H Daniel

2018-05-08

The flexural rigidity of cylindrical specimens, composed of epoxy reinforced by short, magnetized glass fibers, was enhanced using weak magnetic fields (<100 mT). By spatially controlling the magnitude and direction of the field, and thereby the torques and forces acting locally on the fibers, the orientation and concentration of the fillers in the matrix could be tuned prior to curing. Unidirectional alignment of the fibers, achieved using an air-core solenoid, improved the contribution of the fibers to the flexure modulus by a factor of 3. When a ring-shaped permanent magnet was utilized, the glass fibers were migrated preferentially near the rod boundary, and as a result, the contribution of the fibers to the flexure modulus doubled. The fiber length, density, and orientation distributions were extracted by μCT image analysis, allowing comparison of the experimental flexure modulus to a modified rule of mixtures prediction. The ability to magnetically control the fiber distribution in reinforced composites demonstrated in this study may be applied in the fabrication of complex micro- and macroscale structures with spatially variable anisotropy, allowing features such as crack diversion, strengthening of highly loaded regions, as well as economic management of materials and weight.

The vertical structure of the F ring of Saturn from ring-plane crossings

NASA Astrophysics Data System (ADS)

Scharringhausen, Britt R.; Nicholson, Philip D.

2013-11-01

We present a photometric model of the rings of Saturn which includes the main rings and an F ring, inclined to the main rings, with a Gaussian vertical profile of optical depth. This model reproduces the asymmetry in brightness between the east and west ansae of the rings of Saturn that was observed by the Hubble Space Telescope (HST) within a few hours after the Earth ring-plane crossing (RPX) of 10 August 1995. The model shows that during this observation the inclined F ring unevenly blocked the east and west ansae of the main rings. The brightness asymmetry produced by the model is highly sensitive to the vertical thickness and radial optical depth of the F ring. The F-ring model that best matches the observations has a vertical full width at half maximum of 13 ± 7 km and an equivalent depth of 10 ± 4 km. The model also reproduces the shape of the HST profiles of ring brightness vs. distance from Saturn, both before and after the time of ring-plane crossing. Smaller asymmetries observed before the RPX, when the Earth was on the dark side of the rings, cannot be explained by blocking of the main rings by the F ring or vice versa and are probably instead due to the intrinsic longitudinal variation exhibited by the F ring.

Reinforcement in plants.

PubMed

Hopkins, Robin

2013-03-01

A major goal of evolutionary biology is to understand how diverging populations become species. The evolution of reproductive isolation (RI) halts the genomic homogenization caused by gene flow and recombination, and enables differentiation and local adaptations to become fixed between newly forming species. Selection can favor the strengthening of RI through a process termed reinforcement. Reinforcement occurs when selection favors traits that decrease mating between two incipient species in response to costly mating or the production of maladapted hybrids. Although this process has been investigated more frequently in animals, there is also evidence of reinforcement in plants. There are three strategies for the investigation of the process of reinforcement: case studies of species or diverging taxa; experimental evolution studies; and comparative studies. Here, I discuss how all three strategies find evidence consistent with reinforcement occurring in plants. I focus largely on case studies, and use research on Phlox drummondii to illustrate the importance of testing alternative hypotheses. Although the existing evidence suggests that reinforcement can occur, further investigations, particularly using large-scale comparative studies, are needed to determine the importance of reinforcement in plant speciation.

Food reinforcement during infancy.

PubMed

Kong, Kai Ling; Epstein, Leonard H

2016-11-01

The motivation to eat, as operationalized by measuring how hard someone will work for food, is cross-sectionally and prospectively related to obesity. Persons high in food reinforcement consume more calories, and energy intake mediates the relationship between food reinforcement and obesity. Research has shown avid sucking for milk in early infancy predicts later adiposity, and the relationship between food reinforcement and excess body weight has been observed in infants as young as 9months of age. New methodological developments in studying food reinforcement in infants and young children provide the first opportunity to study the origin of food reinforcement. This review seeks to provide background on the measurement of food reinforcement, and to present, for the first time, prenatal and postnatal predictors of infant food reinforcement. Lastly, potential mechanisms for an increasing trajectory of food reinforcement throughout development are proposed. Copyright © 2016 Elsevier Inc. All rights reserved.

Ring-diameter Ratios for Multi-ring Basins Average 2.0(0.5)D

NASA Technical Reports Server (NTRS)

Pike, R. J.; Spudis, P. D.

1985-01-01

The spacing of the concentric rings of planetary impact basins was studied. It is shown that a radial increment of x (sup 0.5) D, where x is about 2.0 and D = ring diameter, separates both (1) adjacent least-squares groups of rings and arcs of multi-ring basins on Mars, Mercury, and the Moon; and (2) adjacent rings of individual basins on the three planets. Statistics for ratios of ring diameters are presented, the first and most-applied parameter of ring spacing. It is found that ratios excluding rings flanking the main ring also have a mean spacing increment of about 2.0. Ratios including such rings, as for the least-squares groups, and (1) above, have a larger increment, averaging 2.1. The F-test indicates, that these spacings of basin ring locations, and mode of ring formation are controlled by the mechanics of the impact event itself, rather than by crustal properties.

Resurgence and alternative-reinforcer magnitude.

PubMed

Craig, Andrew R; Browning, Kaitlyn O; Nall, Rusty W; Marshall, Ciara M; Shahan, Timothy A

2017-03-01

Resurgence is defined as an increase in the frequency of a previously reinforced target response when an alternative source of reinforcement is suspended. Despite an extensive body of research examining factors that affect resurgence, the effects of alternative-reinforcer magnitude have not been examined. Thus, the present experiments aimed to fill this gap in the literature. In Experiment 1, rats pressed levers for single-pellet reinforcers during Phase 1. In Phase 2, target-lever pressing was extinguished, and alternative-lever pressing produced either five-pellet, one-pellet, or no alternative reinforcement. In Phase 3, alternative reinforcement was suspended to test for resurgence. Five-pellet alternative reinforcement produced faster elimination and greater resurgence of target-lever pressing than one-pellet alternative reinforcement. In Experiment 2, effects of decreasing alternative-reinforcer magnitude on resurgence were examined. Rats pressed levers and pulled chains for six-pellet reinforcers during Phases 1 and 2, respectively. In Phase 3, alternative reinforcement was decreased to three pellets for one group, one pellet for a second group, and suspended altogether for a third group. Shifting from six-pellet to one-pellet alternative reinforcement produced as much resurgence as suspending alternative reinforcement altogether, while shifting from six pellets to three pellets did not produce resurgence. These results suggest that alternative-reinforcer magnitude has effects on elimination and resurgence of target behavior that are similar to those of alternative-reinforcer rate. Thus, both suppression of target behavior during alternative reinforcement and resurgence when conditions of alternative reinforcement are altered may be related to variables that affect the value of the alternative-reinforcement source. © 2017 Society for the Experimental Analysis of Behavior.

Resurgence and Alternative-Reinforcer Magnitude

PubMed Central

Craig, Andrew R.; Browning, Kaitlyn O.; Nall, Rusty W.; Marshall, Ciara M.; Shahan, Timothy A.

2017-01-01

Resurgence is defined as an increase in the frequency of a previously reinforced target response when an alternative source of reinforcement is suspended. Despite an extensive body of research examining factors that affect resurgence, the effects of alternative-reinforcer magnitude have not been examined. Thus, the present experiments aimed to fill this gap in the literature. In Experiment 1, rats pressed levers for single-pellet reinforcers during Phase 1. In Phase 2, target-lever pressing was extinguished, and alternative-lever pressing produced either five-pellet, one-pellet, or no alternative reinforcement. In Phase 3, alternative reinforcement was suspended to test for resurgence. Five-pellet alternative reinforcement produced faster elimination and greater resurgence of target-lever pressing than one-pellet alternative reinforcement. In Experiment 2, effects of decreasing alternative-reinforcer magnitude on resurgence were examined. Rats pressed levers and pulled chains for six-pellet reinforcers during Phases 1 and 2, respectively. In Phase 3, alternative reinforcement was decreased to three pellets for one group, one pellet for a second group, and suspended altogether for a third group. Shifting from six-pellet to one-pellet alternative reinforcement produced as much resurgence as suspending alternative reinforcement altogether, while shifting from six pellets to three pellets did not produce resurgence. These results suggest that alternative-reinforcer magnitude has effects on elimination and resurgence of target behavior that are similar to those of alternative-reinforcer rate. Thus, both suppression of target behavior during alternative reinforcement and resurgence when conditions of alternative reinforcement are altered may be related to variables that affect the value of the alternative-reinforcement source. PMID:28194793

Increase in cytosolic calcium maintains plasma membrane integrity through the formation of microtubule ring structure in apoptotic cervical cancer cells induced by trichosanthin.

PubMed

Wang, Ping; Xu, Shujun; Zhao, Kai; Xiao, Bingxiu; Guo, Junming

2009-11-01

This study investigates the role of dysregulated cytosolic free calcium ([Ca(2+)]c) homeostasis on microtubule (MT) ring structure in apoptotic cervical cancer (HeLa) cells induced by trichosanthin (TCS), a type I ribosome inactivating protein (RIP). The TCS-induced decrease in cell viability was significantly enhanced in combination with the specific calcium chelator, EGTA-AM. Sequestration of [Ca(2+)]c markedly disrupted the special MT ring structure. Furthermore, TCS tended to increase LDH release, whereas no significant differences were observed until 48 h of the treatment. In contrast, combined addition of EGTA-AM or colchicine (an inhibitor of tubulin polymerization) significantly reinforced LDH release. The data suggest that TCS-elevated [Ca(2+)]c maintains plasma membrane integrity via the formation of the MT ring structure in apoptotic HeLa cells.

Jupiter's Ring Halo

NASA Technical Reports Server (NTRS)

1997-01-01

A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (km) per picture element (pixel) along the rings; however, because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow peering back toward the Sun; the ring was approximately 2,300,000 kilometers (km) away. The arc on the far right of the image is produced by sunlight scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age.

Jupiter's ring system is composed of three parts -- a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, which lies exterior to the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the far left side of the figure. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow.

A faint mist of particles can be seen above and below the main rings; this vertically extended, toroidal 'halo' is unusual in planetary rings, and is probably caused by electromagnetic forces which can push small grains out of the ring plane. Halo material is present across this entire image, implying that it reaches more than 27,000 km above the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. In order to accentuate faint features in the image, different brightnesses are shown through color, with the brightest

Saturn Ring

NASA Image and Video Library

2007-12-12

Like Earth, Saturn has an invisible ring of energetic ions trapped in its magnetic field. This feature is known as a "ring current." This ring current has been imaged with a special camera on Cassini sensitive to energetic neutral atoms. This is a false color map of the intensity of the energetic neutral atoms emitted from the ring current through a processed called charged exchange. In this process a trapped energetic ion steals and electron from cold gas atoms and becomes neutral and escapes the magnetic field. The Cassini Magnetospheric Imaging Instrument's ion and neutral camera records the intensity of the escaping particles, which provides a map of the ring current. In this image, the colors represent the intensity of the neutral emission, which is a reflection of the trapped ions. This "ring" is much farther from Saturn (roughly five times farther) than Saturn's famous icy rings. Red in the image represents the higher intensity of the particles, while blue is less intense. Saturn's ring current had not been mapped before on a global scale, only "snippets" or areas were mapped previously but not in this detail. This instrument allows scientists to produce movies (see PIA10083) that show how this ring changes over time. These movies reveal a dynamic system, which is usually not as uniform as depicted in this image. The ring current is doughnut shaped but in some instances it appears as if someone took a bite out of it. This image was obtained on March 19, 2007, at a latitude of about 54.5 degrees and radial distance 1.5 million kilometres (920,000 miles). Saturn is at the center, and the dotted circles represent the orbits of the moon's Rhea and Titan. The Z axis points parallel to Saturn's spin axis, the X axis points roughly sunward in the sun-spin axis plane, and the Y axis completes the system, pointing roughly toward dusk. The ion and neutral camera's field of view is marked by the white line and accounts for the cut-off of the image on the left. The

Jupiter Ring

NASA Image and Video Library

2000-03-23

First evidence of a ring around the planet Jupiter is seen in this photograph taken by Voyager 1 on March 4, 1979. The multiple exposure of the extremely thin faint ring appears as a broad light band crossing the center of the picture. The edge of the ring is 1,212,000 km from the spacecraft and 57,000 km from the visible cloud deck of Jupiter. The background stars look like broken hair pins because of spacecraft motion during the 11 minute 12 second exposure. The wavy motion of the star trails is due to the ultra-slow natural oscillation of the spacecraft (with a period of 78 seconds). The black dots are geometric calibration points in the camera. The ring thickness is estimated to be 30 km or less. The photograph was part of a sequence planned to search for such rings in Jupiter's equatorial plane. The ring has been invisible from Earth because of its thinness and its transparency when viewed at any angle except straight on. JPL manages and controls the Voyager Project for NASA's Office of Space Science. http://photojournal.jpl.nasa.gov/catalog/PIA02251

Reinforced Honeycomb Panels

NASA Technical Reports Server (NTRS)

Bhat, Balakrishna T.; Akutagawa, Wesley; Wang, Taylor G.; Barber, Dan

1989-01-01

New honeycomb panel structure has increased strength and stiffness with little increase in weight. Some or all of walls of honeycomb cells reinforced with honeycomb panels having smaller cells, lightweight foam, or other reinforcing material. Strong, lightweight reinforced panels used in aircraft, car and truck bodies, cabinets for equipment and appliances, and buildings.

Reinforcement Sensitivity Underlying Treatment-Seeking Smokers’ Affect, Smoking Reinforcement Motives, and Affective Responses

PubMed Central

Cui, Yong; Robinson, Jason D.; Engelmann, Jeffrey M.; Lam, Cho Y.; Minnix, Jennifer A.; Karam-Hage, Maher; Wetter, David W.; Dani, John A.; Kosten, Thomas R.; Cinciripini, Paul M.

2014-01-01

Nicotine dependence has been suggested to be related to reinforcement sensitivity, which encompasses behavioral predispositions either to avoid aversive (behavioral inhibition) or to approach appetitive (behavioral activation) stimuli. Reinforcement sensitivity may shape motives for nicotine use and offer potential targets for personalized smoking cessation therapy. However, little is known regarding how reinforcement sensitivity is related to motivational processes implicated in the maintenance of smoking. Additionally, women and men differ in reinforcement sensitivity, and such difference may cause distinct relationships between reinforcement sensitivity and motivational processes for female and male smokers. In this study, we characterized reinforcement sensitivity in relation to affect, smoking-related reinforcement motives, and affective responses, using self-report and psychophysiological measures, in over 200 smokers before treating them. The Behavioral Inhibition/Activation Scales (BIS/BAS; Carver & White, 1994) was used to measure reinforcement sensitivity. In female and male smokers, BIS was similarly associated with negative affect and negative reinforcement of smoking. But positive affect was positively associated with BAS Drive scores in male smokers, and this association was reversed in female smokers. BIS was positively associated with corrugator electromyographic reactivity towards negative stimuli and left frontal electroencephalogram alpha asymmetry. Female and male smokers showed similar relationships for these physiological measures. These findings suggest that reinforcement sensitivity underpins important motivational processes (e.g., affect), and gender is a moderating factor for these relationships. Future personalized smoking intervention, particularly among more dependent treatment-seeking smokers, may experiment to target individual differences in reinforcement sensitivity. PMID:25621416

Topological ring currents in the "empty" ring of benzo-annelated perylenes.

PubMed

Dickens, Timothy K; Mallion, Roger B

2011-01-27

Cyclic conjugation in benzo-annelated perylenes is examined by means of the topological π-electron ring currents calculated for each of their constituent rings, in a study that is an exact analogy of a recent investigation by Gutman et al. based on energy-effect values for the corresponding rings in each of these structures. "Classical" approaches, such as Kekulé structures, Clar "sextet" formulas, and circuits of conjugation, predict that the central ring in perylene is "empty" and thus contributes negligibly to cyclic conjugation. However, conclusions from the present calculations of topological ring currents agree remarkably with those arising from the earlier study involving energy-effect values in that, contrary to what would be predicted from the classical approaches, rings annelated in an angular fashion relative to the central ring of these perylene structures materially increase the extent of that ring's involvement in cyclic conjugation. It is suggested that such close quantitative agreement between the predictions of these two superficially very different indices (energy effect and topological ring current) might be due to the fact that, ultimately, both depend, albeit in ostensibly quite different ways, only on an adjacency matrix that contains information about the carbon-carbon connectivity of the conjugated system in question.

Flexural strength using Steel Plate, Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) on reinforced concrete beam in building technology

NASA Astrophysics Data System (ADS)

Tarigan, Johannes; Patra, Fadel Muhammad; Sitorus, Torang

2018-03-01

Reinforced concrete structures are very commonly used in buildings because they are cheaper than the steel structures. But in reality, many concrete structures are damaged, so there are several ways to overcome this problem, by providing reinforcement with Fiber Reinforced Polymer (FRP) and reinforcement with steel plates. Each type of reinforcements has its advantages and disadvantages. In this study, researchers discuss the comparison between flexural strength of reinforced concrete beam using steel plates and Fiber Reinforced Polymer (FRP). In this case, the researchers use Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) as external reinforcements. The dimension of the beams is 15 x 25 cm with the length of 320 cm. Based on the analytical results, the strength of the beam with CFRP is 1.991 times its initial, GFRP is 1.877 times while with the steel plate is 1.646 times. Based on test results, the strength of the beam with CFRP is 1.444 times its initial, GFRP is 1.333 times while the steel plate is 1.167 times. Based on these test results, the authors conclude that beam with CFRP is the best choice for external reinforcement in building technology than the others.

Nitrile O-ring Cracking: A Case of Vacuum Flange O-ring Failures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dees, Craig

2016-07-01

A review of recent nitrile O-ring failures in ISO-KF vacuum flange connections in glovebox applications is presented. An investigation of a single “isolated” o-ring failure leads to the discovery of cracked nitrile o-rings in a glovebox atmospheric control unit. The initial cause of the o-ring failure is attributed to ozone degradation. However, additional investigation reveals nitrile o-ring cracking on multiple gloveboxes and general purpose piping, roughly 85% of the nitrile o-rings removed for inspection show evidence of visible cracking after being in service for 18 months or less. The results of material testing and ambient air testing is presented, elevatedmore » ozone levels are not found. The contributing factors of o-ring failure, including nitrile air sensitivity, inadequate storage practices, and poor installation techniques, are discussed. A discussion of nitrile o-ring material properties, the benefits and limitations, and alternate materials are discussed. Considerations for o-ring material selection, purchasing, storage, and installation are presented in the context of lessons learned from the nitrile o-ring cracking investigation. This paper can be presented in 20 minutes and does not require special accommodations or special audio visual devices.« less

DC-Powered Jumping Ring

NASA Astrophysics Data System (ADS)

Jeffery, Rondo N.; Amiri, Farhang

2016-02-01

The classroom jumping ring demonstration is nearly always performed using alternating current (AC), in which the ring jumps or flies off the extended iron core when the switch is closed. The ring jumps higher when cooled with liquid nitrogen (LN2). We have performed experiments using DC to power the solenoid and find similarities and significant differences from the AC case. In particular, the ring does not fly off the core but rises a short distance and then falls back. If the ring jumps high enough, the rising and the falling motion of the ring does not follow simple vertical motion of a projectile. This indicates that there are additional forces on the ring in each part of its motion. Four possible stages of the motion of the ring with DC are identified, which result from the ring current changing directions during the jump in response to a changing magnetic flux through the moving ring.

Oxygen Abundances in the Rings of Polar-Ring Galaxies

NASA Astrophysics Data System (ADS)

Radtke, I. R.; Eskridge, P. B.; Pogge, R. W.

2003-05-01

Polar ring galaxies (PRGs) are typically early-type (S0 or E) galaxies surrounded by rings of gas, dust, and stars orbiting nearly perpendicular to the principle plane of the host galaxy (Whitmore et al. 1990 AJ 100 1489). Given that PRGs have two separate, perpendicular axes of rotation, it is clear on dynamical grounds that PRGs are the products of merger events between two galaxies, but are observed in a state where two distinct kinematic and morphological structures are still apparent. As such, they present a unique opportunity to study merger events in systems where the debris is not confused with material from the host. Our understanding of the relative importance of polar ring systems in the overall process of galaxy evolution is confounded by our lack of knowledge regarding the typical lifetimes and evolutionary histories of polar rings. A crucial factor for understanding the formation and evolution of PRGs is information regarding the elemental abundances of the ring material. Polar rings are typically rich in {\\protectH 2} regions. Optical spectroscopy of these {\\protectH 2} regions can tell us their density, temperature, and oxygen abundance. Our earlier work (Eskridge & Pogge 1997 ApJ 486 259) revealed roughly Solar oxygen abundances for {\\protectH 2} regions in the polar ring of NGC 2685. We have extended this project, and now have spectra for six PRGs. Analysis of the data for II Zw 73 and UGC 7576 reveal the polar rings of these galaxies to have {\\protectH 2} region oxygen abundances in the range 0.3 to 0.6 Solar, substantially less than found for NGC 2685. Abundances in this range are much easier to explain with conventional models of chemical enrichment and polar ring formation. We shall present results for our full sample. Taken as a whole, this sample will provide a clear foundation for the typical chemical enrichment patterns in polar rings, and thus provide a clearer understanding of the formation and evolution of these curious objects. We

Saturn's F-Ring

NASA Technical Reports Server (NTRS)

2000-01-01

This narrow-angle camera image of Saturn's F Ring was taken through the Clear filter while at a distance of 6.9 million km from Saturn on 8 November 1980. The brightness variations of this tightly-constrained ring shown here indicate that the ring is less uniform in makeup than the larger rings. JPL managed the Voyager Project for NASA's Office of Space Science

Planetary Rings

NASA Astrophysics Data System (ADS)

Nicholson, P. D.

2001-11-01

A revolution in the studies in planetary rings studies occurred in the period 1977--1981, with the serendipitous discovery of the narrow, dark rings of Uranus, the first Voyager images of the tenuous jovian ring system, and the many spectacular images returned during the twin Voyager flybys of Saturn. In subsequent years, ground-based stellar occultations, HST observations, and the Voyager flybys of Uranus (1986) and Neptune (1989), as well as a handful of Galileo images, provided much additional information. Along with the completely unsuspected wealth of detail these observations revealed came an unwelcome problem: are the rings ancient or are we privileged to live at a special time in history? The answer to this still-vexing question may lie in the complex gravitational interactions recent studies have revealed between the rings and their retinues of attendant satellites. Among the four known ring systems, we see elegant examples of Lindblad and corotation resonances (first invoked in the context of galactic disks), electromagnetic resonances, spiral density waves and bending waves, narrow ringlets which exhibit internal modes due to collective instabilities, sharp-edged gaps maintained via tidal torques from embedded moonlets, and tenuous dust belts created by meteoroid impact onto parent bodies. Perhaps most puzzling is Saturn's multi-stranded, clumpy F ring, which continues to defy a simple explanation 20 years after it was first glimpsed in grainy images taken by Pioneer 11. Voyager and HST images reveal a complex, probably chaotic, dynamical interaction between unseen parent bodies within this ring and its two shepherd satellites, Pandora and Prometheus. The work described here reflects contributions by Joe Burns, Jeff Cuzzi, Luke Dones, Dick French, Peter Goldreich, Colleen McGhee, Carolyn Porco, Mark Showalter, and Bruno Sicardy, as well as those of the author. This research has been supported by NASA's Planetary Geology and Geophysics program and the

Reinforcement sensitivity underlying treatment-seeking smokers' affect, smoking reinforcement motives, and affective responses.

PubMed

Cui, Yong; Robinson, Jason D; Engelmann, Jeffrey M; Lam, Cho Y; Minnix, Jennifer A; Karam-Hage, Maher; Wetter, David W; Dani, John A; Kosten, Thomas R; Cinciripini, Paul M

2015-06-01

Nicotine dependence has been suggested to be related to reinforcement sensitivity, which encompasses behavioral predispositions either to avoid aversive (behavioral inhibition) or to approach appetitive (behavioral activation) stimuli. Reinforcement sensitivity may shape motives for nicotine use and offer potential targets for personalized smoking cessation therapy. However, little is known regarding how reinforcement sensitivity is related to motivational processes implicated in the maintenance of smoking. Additionally, women and men differ in reinforcement sensitivity, and such difference may cause distinct relationships between reinforcement sensitivity and motivational processes for female and male smokers. In this study, the authors characterized reinforcement sensitivity in relation to affect, smoking-related reinforcement motives, and affective responses, using self-report and psychophysiological measures, in over 200 smokers before treating them. The Behavioral Inhibition/Activation Scales (BIS/BAS; Carver & White, 1994) was used to measure reinforcement sensitivity. In female and male smokers, BIS was similarly associated with negative affect and negative reinforcement of smoking. However, positive affect was positively associated with BAS Drive scores in male smokers, and this association was reversed in female smokers. BIS was positively associated with corrugator electromyographic reactivity toward negative stimuli and left frontal electroencephalogram alpha asymmetry. Female and male smokers showed similar relationships for these physiological measures. These findings suggest that reinforcement sensitivity underpins important motivational processes (e.g., affect), and gender is a moderating factor for these relationships. Future personalized smoking intervention, particularly among more dependent treatment-seeking smokers, may experiment to target individual differences in reinforcement sensitivity. (PsycINFO Database Record (c) 2015 APA, all rights

Numerical Modeling of Local Penetration of Chloride-Containing Medium into Construction Elements Made of Reinforced Concrete

NASA Astrophysics Data System (ADS)

Ovchinnikov, I. I.; Snezhkina, O. V.; Ovchinnikov, I. G.

2017-11-01

The task of modeling the kinetics of chloride-containing medium penetration into construction elements out of reinforced concrete that have partially damaged anti-corrosion protective coatings is being discussed. As a result, chlorides penetrate the construction element via local surface areas which leads to irregularities between chloride dispersion volumes. The kinetics of chloride penetration is described by the equation of diffusion to solve which the CONDUCT software complex by professor S. Patankar was used. The methodology used to solve the diffusional equation is described. The results of the evaluation of concentration field in the axial section of a cylindrical construction element, which was centrally reinforced, are given. The chloride diffusion was symmetrical to the axis, the medium was applied through the central ring area equal to one third of the side surface area while the rest of the surface was isolated. It was shown that the methodology of evaluation and its algorithm allow one to evaluate the concentration field of chlorides in reinforced concrete structural elements under local or asymmetrical action of the chloride - containing medium. The example given illustrates that after a certain time interval critical the concentration of chlorides develops even in protected areas which are located far from the initial damaged area. This means that the corrosion destruction of reinforced elements develops not only in the immediate damage area, but also further away from it.

The Ring Sculptor

NASA Image and Video Library

2006-09-08

Prometheus zooms across the Cassini spacecraft field of view, attended by faint streamers and deep gores in the F ring. This movie sequence of five images shows the F ring shepherd moon shaping the ring inner edge

Mechanisms of ring chromosome formation, ring instability and clinical consequences.

PubMed

Guilherme, Roberta S; Meloni, Vera F Ayres; Kim, Chong A; Pellegrino, Renata; Takeno, Sylvia S; Spinner, Nancy B; Conlin, Laura K; Christofolini, Denise M; Kulikowski, Leslie D; Melaragno, Maria I

2011-12-21

The breakpoints and mechanisms of ring chromosome formation were studied and mapped in 14 patients. Several techniques were performed such as genome-wide array, MLPA (Multiplex Ligation-Dependent Probe Amplification) and FISH (Fluorescent in situ Hybridization). The ring chromosomes of patients I to XIV were determined to be, respectively: r(3)(p26.1q29), r(4)(p16.3q35.2), r(10)(p15.3q26.2), r(10)(p15.3q26.13), r(13)(p13q31.1), r(13)(p13q34), r(14)(p13q32.33), r(15)(p13q26.2), r(18)(p11.32q22.2), r(18)(p11.32q21.33), r(18)(p11.21q23), r(22)(p13q13.33), r(22)(p13q13.2), and r(22)(p13q13.2). These rings were found to have been formed by different mechanisms, such as: breaks in both chromosome arms followed by end-to-end reunion (patients IV, VIII, IX, XI, XIII and XIV); a break in one chromosome arm followed by fusion with the subtelomeric region of the other (patients I and II); a break in one chromosome arm followed by fusion with the opposite telomeric region (patients III and X); fusion of two subtelomeric regions (patient VII); and telomere-telomere fusion (patient XII). Thus, the r(14) and one r(22) can be considered complete rings, since there was no loss of relevant genetic material. Two patients (V and VI) with r(13) showed duplication along with terminal deletion of 13q, one of them proved to be inverted, a mechanism known as inv-dup-del. Ring instability was detected by ring loss and secondary aberrations in all but three patients, who presented stable ring chromosomes (II, XIII and XIV). We concluded that the clinical phenotype of patients with ring chromosomes may be related with different factors, including gene haploinsufficiency, gene duplications and ring instability. Epigenetic factors due to the circular architecture of ring chromosomes must also be considered, since even complete ring chromosomes can result in phenotypic alterations, as observed in our patients with complete r(14) and r(22).

Radiographic evaluation of BFX acetabular component position in dogs.

PubMed

Renwick, Alasdair; Gemmill, Toby; Pink, Jonathan; Brodbelt, David; McKee, Malcolm

2011-07-01

To assess the reliability of radiographic measurement of angle of lateral opening (ALO) and angle of version of BFX acetabular cups. In vitro radiographic study. BFX cups (24, 28, and 32 mm). Total hip replacement constructs (cups, 17 mm femoral head and a #7 CFX stem) were mounted on an inclinometer. Ventrodorsal radiographs were obtained with ALO varying between 21° and 70° and inclination set at 0°, 10°, 20°, and 30°. Radiographs were randomized using a random sequence generator. Three observers blinded to the radiograph order assessed ALO using 3 methods: (1) an ellipse method based on trigonometry; (2) using a measurement from the center of the femoral head to the truncated surface of the cup; (3) by visual estimation using a reference chart. Version was measured by assessing the ventral edge of the truncated surface. ALO methods 2 and 3 were accurate and precise to within 10° and were significantly more accurate and precise than method 1 (P < .001). All methods were significantly less accurate with increasing inclination. Version measurement was accurate and precise to within 7° with 0-20° of inclination, but significantly less accurate with 30° of inclination. Methods 2 and 3, but not method 1, were sufficiently accurate and precise to be clinically useful. Version measurement was clinically useful when inclination was ≤ 20°. © Copyright 2011 by The American College of Veterinary Surgeons.

Saddle-shaped mitral valve annuloplasty rings experience lower forces compared with flat rings.

PubMed

Jensen, Morten O; Jensen, Henrik; Smerup, Morten; Levine, Robert A; Yoganathan, Ajit P; Nygaard, Hans; Hasenkam, J Michael; Nielsen, Sten L

2008-09-30

New insight into the 3D dynamic behavior of the mitral valve has prompted a reevaluation of annuloplasty ring designs. Force balance analysis indicates correlation between annulus forces and stresses in leaflets and chords. Improving this stress distribution can intuitively enhance the durability of mitral valve repair. We tested the hypothesis that saddle-shaped annuloplasty rings have superior uniform systolic force distribution compared with a nonuniform force distribution in flat annuloplasty rings. Sixteen 80-kg pigs had a flat (n=8) or saddle-shaped (n=8) mitral annuloplasty ring implanted. Mitral annulus 3D dynamic geometry was obtained with sonomicrometry before ring insertion. Strain gauges mounted on dedicated D-shaped rigid flat and saddle-shaped annuloplasty rings provided the intraoperative force distribution perpendicular to the annular plane. Average systolic annular height to commissural width ratio before ring implantation was 14.0%+/-1.6%. After flat and saddle shaped ring implantation, the annulus was fixed in the diastolic (9.0%+/-1.0%) and systolic (14.3%+/-1.3%) configuration, respectively (P<0.01). Force accumulation was seen from the anterior (0.72N+/-0.14N) and commissural annular segments (average 1.38N+/-0.27N) of the flat rings. In these segments, the difference between the 2 types of rings was statistically significant (P<0.05). The saddle-shaped annuloplasty rings did not experience forces statistically significantly larger than zero in any annular segments. Saddle-shaped annuloplasty rings provide superior uniform annular force distribution compared to flat rings and appear to represent a configuration that minimizes out-of-plane forces that could potentially be transmitted to leaflets and chords. This may have important implications for annuloplasty ring selections.

So Long, C Ring

NASA Image and Video Library

2017-11-13

Saturn's C ring is home to a surprisingly rich array of structures and textures. Much of the structure seen in the outer portions of Saturn's rings is the result of gravitational perturbations on ring particles by moons of Saturn. Such interactions are called resonances. However, scientists are not clear as to the origin of the structures seen in this image which has captured an inner ring region sparsely populated with particles, making interactions between ring particles rare, and with few satellite resonances. In this image, a bright and narrow ringlet located toward the outer edge of the C ring is flanked by two broader features called plateaus, each about 100 miles (160 kilometers) wide. Plateaus are unique to the C ring. Cassini data indicates that the plateaus do not necessarily contain more ring material than the C ring at large, but the ring particles in the plateaus may be smaller, enhancing their brightness. This view looks toward the sunlit side of the rings from about 53 degrees above the ring plane. The image was taken in green light with the Cassini spacecraft narrow-angle camera on Aug. 14, 2017. The view was acquired at a distance of approximately 117,000 miles (189,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 74 degrees. Image scale is 3,000 feet (1 kilometer) per pixel. The Cassini spacecraft ended its mission on Sept. 15, 2017. https://photojournal.jpl.nasa.gov/catalog/PIA21356

Thermal evolution behavior and fluid dynamics during laser additive manufacturing of Al-based nanocomposites: Underlying role of reinforcement weight fraction

NASA Astrophysics Data System (ADS)

Gu, Dongdong; Yuan, Pengpeng

2015-12-01

In this study, a three-dimensional transient computational fluid dynamics model was established to investigate the influence of reinforcement weight fraction on thermal evolution behavior and fluid dynamics during selective laser melting (SLM) additive manufacturing of TiC/AlSi10Mg nanocomposites. The powder-to-solid transition and nonlinear variation of thermal physical properties of as-used materials were considered in the numerical model, using the Gaussian distributed volumetric heat source. The simulation results showed that the increase of operating temperature and the resultant formation of larger melt pool were caused by the increase of weight fraction of reinforcement. The Marangoni convection was intensified using a larger reinforcement content, accelerating the coupled motion of fluid and solid particles. The circular flows appeared when the TiC content reached 5.0 wt. % and the larger-sized circular flows were present as the reinforcement content increased to 7.5 wt. %. The experimental study on surface morphologies and microstructures on the polished sections of SLM-processed TiC/AlSi10Mg nanocomposite parts was performed. A considerably dense and smooth surface free of any balling effect and pore formation was obtained when the reinforcement content was optimized at 5.0 wt. %, due to the sufficient liquid formation and moderate Marangoni flow. Novel ring-structured reinforcing particulates were tailored because of the combined action of the attractive effect of centripetal force and repulsive force, which was consistent with the simulation results.

A multiscale model for reinforced concrete with macroscopic variation of reinforcement slip

NASA Astrophysics Data System (ADS)

Sciegaj, Adam; Larsson, Fredrik; Lundgren, Karin; Nilenius, Filip; Runesson, Kenneth

2018-06-01

A single-scale model for reinforced concrete, comprising the plain concrete continuum, reinforcement bars and the bond between them, is used as a basis for deriving a two-scale model. The large-scale problem, representing the "effective" reinforced concrete solid, is enriched by an effective reinforcement slip variable. The subscale problem on a Representative Volume Element (RVE) is defined by Dirichlet boundary conditions. The response of the RVEs of different sizes was investigated by means of pull-out tests. The resulting two-scale formulation was used in an FE^2 analysis of a deep beam. Load-deflection relations, crack widths, and strain fields were compared to those obtained from a single-scale analysis. Incorporating the independent macroscopic reinforcement slip variable resulted in a more pronounced localisation of the effective strain field. This produced a more accurate estimation of the crack widths than the two-scale formulation neglecting the effective reinforcement slip variable.

Reinforcement of timber beams with carbon fibers reinforced plastics

NASA Astrophysics Data System (ADS)

Gugutsidze, G.; Draškovič, F.

2010-06-01

Wood is a polymeric material with many valuable features and which also lacks some negative features. In order to keep up with high construction rates and the minimization of negative effects, wood has become one of the most valuable materials in modern engineering. But the use of timber material economically is also an actual problem in order to protect the environment and improve natural surroundings. A panel of scientists is interested in solving these problems and in creating rational structures, where timber can be used efficiently. These constructions are as follows: glue-laminated (gluelam), composed and reinforced wooden constructions. Composed and reinforced wooden constructions are examined less, but according to researches already carried out, it is clear that significant work can be accomplished in creating rational, highly effective and economic timber constructions. The paper deals with research on the formation of composed fiber-reinforced beams (CFRP) made of timber and provide evidence of their effectiveness. The aim of the paper is to investigate cross-bending of CFRP-reinforced gluelaminated timber beams. According to the results we were able to determine the additional effectiveness of reinforcement with CFRP (which depends on the CFRP material's quality, quantity and module of elasticity) on the mechanical features of timber and a whole beam.

Ring faults and ring dikes around the Orientale basin on the Moon.

PubMed

Andrews-Hanna, Jeffrey C; Head, James W; Johnson, Brandon; Keane, James T; Kiefer, Walter S; McGovern, Patrick J; Neumann, Gregory A; Wieczorek, Mark A; Zuber, Maria T

2018-08-01

The Orientale basin is the youngest and best-preserved multiring impact basin on the Moon, having experienced only modest modification by subsequent impacts and volcanism. Orientale is often treated as the type example of a multiring basin, with three prominent rings outside of the inner depression: the Inner Rook Montes, the Outer Rook Montes, and the Cordillera. Here we use gravity data from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission to reveal the subsurface structure of Orientale and its ring system. Gradients of the gravity data reveal a continuous ring dike intruded into the Outer Rook along the plane of the fault associated with the ring scarp. The volume of this ring dike is ~18 times greater than the volume of all extrusive mare deposits associated with the basin. The gravity gradient signature of the Cordillera ring indicates an offset along the fault across a shallow density interface, interpreted to be the base of the low-density ejecta blanket. Both gravity gradients and crustal thickness models indicate that the edge of the central cavity is shifted inward relative to the equivalent Inner Rook ring at the surface. Models of the deep basin structure show inflections along the crust-mantle interface at both the Outer Rook and Cordillera rings, indicating that the basin ring faults extend from the surface to at least the base of the crust. Fault dips range from 13-22° for the Cordillera fault in the northeastern quadrant, to 90° for the Outer Rook in the northwestern quadrant. The fault dips for both outer rings are lowest in the northeast, possibly due to the effects of either the direction of projectile motion or regional gradients in pre-impact crustal thickness. Similar ring dikes and ring faults are observed around the majority of lunar basins.

Fiber reinforced cementitious matrix (FRCM) composites for reinforced concrete strengthening.

DOT National Transportation Integrated Search

2013-07-01

Fiber-reinforced composite systems are widely used for strengthening, repairing, and rehabilitation of reinforced concrete structural : members. A promising newly-developed type of composite, comprised of fibers and an inorganic cement-based matrix, ...

Staple line reinforcement during sleeve gastrectomy with a new type of reinforced stapler.

PubMed

El Moussaoui, Imad; Limbga, Augustin; Mehdi, Abdelilah

2018-04-01

Bleeding and staple-line leak, are the most common complications of laparoscopic sleeve gastrectomy. To decrease the incidence of this complications, a variety of intraoperative reinforcement of staple line is used. Reinforced GIA™ is a new automatic suture device with pre-attached synthetic tissue reinforcement, but no study has evaluated its use in sleeve gastrectomy. The objective of this study is to evaluate the efficacy and safety of this new staple line reinforcement technique in laparoscopic sleeve gastrectomy. We conducted a retrospective review of 290 patients who underwent laparoscopic sleeve gastrectomy between January 2013 and January 2016 in which reinforced GIA™ or standard GIA™ was used. Patients preoperative characteristics, Operative time, staple line leaks, staple line bleeds, stenosis, and complications requiring reoperation were collected. A total of 187 laparoscopic sleeve gastrectomy were performed with standard GIA and 103 with reinforced GIA™. Patient characteristics were not significantly different between the groups. The average operating time in the standard GIA group is 57.41±16.44 min against 50.9±14.12 min in the reinforced GIA group (P=0.006). Two staple line leaks developed in the standard GIA group and reoperated against no patients in the reinforced GIA group, without significant difference between the both groups (P=0.66). Staple line bleeds are less in the reinforced GIA group, only 23 (22.3%) against 78 (41.7%) cases in the standard GIA group (P=0.001). No patients of both groups developed gastric sleeve stenosis. During laparoscopic sleeve gastrectomy, the use of a reinforced stapler significantly reduces the operative time and staple line bleeding. No significant difference is evidenced in terms of reduction of staple line leaks with this reinforced stapler.

Evaluation of a Shape Memory Alloy Reinforced Annuloplasty Band for Minimally Invasive Mitral Valve Repair

PubMed Central

Purser, Molly F.; Richards, Andrew L.; Cook, Richard C.; Osborne, Jason A.; Cormier, Denis R.; Buckner, Gregory D.

2013-01-01

Purpose An in vitro study using explanted porcine hearts was conducted to evaluate a novel annuloplasty band, reinforced with a two-phase, shape memory alloy, designed specifically for minimally invasive mitral valve repair. Description In its rigid (austenitic) phase, this band provides the same mechanical properties as the commercial semi-rigid bands. In its compliant (martensitic) phase, this band is flexible enough to be introduced through an 8-mm trocar and is easily manipulated within the heart. Evaluation In its rigid phase, the prototype band displayed similar mechanical properties to commercially available semi-rigid rings. Dynamic flow testing demonstrated no statistical differences in the reduction of mitral valve regurgitation. In its flexible phase, the band was easily deployed through an 8-mm trocar, robotically manipulated and sutured into place. Conclusions Experimental results suggest that the shape memory alloy reinforced band could be a viable alternative to flexible and semi-rigid bands in minimally invasive mitral valve repair. PMID:19766827

Vascular ring

MedlinePlus

... with aberrant subclavian and left ligamentum ateriosus; Congenital heart defect - vascular ring; Birth defect heart - vascular ring ... accounts for less than 1% of all congenital heart problems. The condition occurs as often in males ...

Stable forming conditions and geometrical expansion of L-shape rings in ring rolling process

NASA Astrophysics Data System (ADS)

Quagliato, Luca; Berti, Guido A.; Kim, Dongwook; Kim, Naksoo

2018-05-01

Based on previous research results concerning the radial-axial ring rolling process of flat rings, this paper details an innovative approach for the determination of the stable forming conditions to successfully simulate the radial ring rolling process of L-shape profiled rings. In addition to that, an analytical model for the estimation of the geometrical expansion of L-shape rings from its initial flat ring preform is proposed and validated by comparing its results with those of numerical simulations. By utilizing the proposed approach, steady forming conditions could be achieved, granting a uniform expansion of the ring throughout the process for all of the six tested cases of rings having the final outer diameter of the flange ranging from 545mm and 1440mm. The validation of the proposed approach allowed concluding that the geometrical expansion of the ring, as estimated by the proposed analytical model, is in good agreement with the results of the numerical simulation, with a maximum error of 2.18%, in the estimation of the ring wall diameter, 1.42% of the ring flange diameter and 1.87% for the estimation of the inner diameter of the ring, respectively.

Saturn’s Ring Rain: Initial Estimates of Ring Mass Loss Rates

NASA Astrophysics Data System (ADS)

Moore, Luke; O'Donoghue, J.; Mueller-Wodarg, I.; Mendillo, M.

2013-10-01

We estimate rates of mass loss from Saturn’s rings based on ionospheric model reproductions of derived H3+ column densities. On 17 April 2011 over two hours of near-infrared spectral data were obtained of Saturn using the Near InfraRed Spectrograph (NIRSPEC) instrument on the 10-m Keck II telescope. The intensity of two bright H3+ rotational-vibrational emission lines was visible from nearly pole to pole, allowing low-latitude ionospheric emissions to be studied for the first time, and revealing significant latitudinal structure, with local extrema in one hemisphere being mirrored at magnetically conjugate latitudes in the opposite hemisphere. Even more striking, those minima and maxima mapped to latitudes of increased or increased density in Saturn’s rings, implying a direct ring-atmosphere connection in which charged water group particles from the rings are guided by magnetic field lines as they “rain” down upon the atmosphere. Water products act to quench the local ionosphere, and therefore modify the observed H3+ densities. Using the Saturn Thermosphere Ionosphere Model (STIM), a 3-D model of Saturn’s upper atmosphere, we derive the rates of water influx required from the rings in order to reproduce the observed H3+ column densities. As a unique pair of conjugate latitudes map to a specific radial distance in the ring plane, the derived water influxes can equivalently be described as rates of ring mass erosion as a function of radial distance in the ring plane, and therefore also allow for an improved estimate of the lifetime of Saturn’s rings.

Deformation of the Durom acetabular component and its impact on tribology in a cadaveric model--a simulator study.

PubMed

Liu, Feng; Chen, Zhefeng; Gu, Yanqing; Wang, Qing; Cui, Weiding; Fan, Weimin

2012-01-01

Recent studies have shown that the acetabular component frequently becomes deformed during press-fit insertion. The aim of this study was to explore the deformation of the Durom cup after implantation and to clarify the impact of deformation on wear and ion release of the Durom large head metal-on-metal (MOM) total hips in simulators. Six Durom cups impacted into reamed acetabula of fresh cadavers were used as the experimental group and another 6 size-paired intact Durom cups constituted the control group. All 12 Durom MOM total hips were put through a 3 million cycle (MC) wear test in simulators. The 6 cups in the experimental group were all deformed, with a mean deformation of 41.78 ± 8.86 µm. The average volumetric wear rate in the experimental group and in the control group in the first million cycle was 6.65 ± 0.29 mm(3)/MC and 0.89 ± 0.04 mm(3)/MC (t = 48.43, p = 0.000). The ion levels of Cr and Co in the experimental group were also higher than those in the control group before 2.0 MC. However there was no difference in the ion levels between 2.0 and 3.0 MC. This finding implies that the non-modular acetabular component of Durom total hip prosthesis is likely to become deformed during press-fit insertion, and that the deformation will result in increased volumetric wear and increased ion release. This study was determined to explore the deformation of the Durom cup after implantation and to clarify the impact of deformation on wear and ion release of the prosthesis. Deformation of the cup after implantation increases the wear of MOM bearings and the resulting ion levels. The clinical use of the Durom large head prosthesis should be with great care.

The Enceladus Ring

NASA Technical Reports Server (NTRS)

2006-01-01

[figure removed for brevity, see original site] The Enceladus Ring (labeled)

This excellent view of the faint E ring -- a ring feature now known to be created by Enceladus -- also shows two of Saturn's small moons that orbit within the ring, among a field of stars in the background.

The E ring extends from three to eight Saturn radii -- about 180,000 kilometers (118,000 miles) to 482,000 kilometers (300,000 miles). Its full extent is not visible in this view.

Calypso (22 kilometers, or 14 miles across) and Helene (32 kilometers, or 20 miles across) orbit within the E ring's expanse. Helene skirts the outer parts of the E ring, but here it is projected in front of a region deeper within the ring.

Calypso and Helene are trojan satellites, or moons that orbit 60 degrees in front or behind a larger moon. Calypso is a Tethys trojan and Helene is a trojan of Dione.

An interesting feature of note in this image is the double-banded appearance of the E-ring, which is created because the ring is somewhat fainter in the ringplane than it is 500-1,000 kilometers (300-600 miles) above and below the ringplane. This appearance implies that the particles in this part of the ring have nonzero inclinations (a similar affect is seen in Jupiter's gossamer ring). An object with a nonzero inclination does not orbit exactly at Saturn's ringplane. Instead, its orbit takes it above and below the ringplane. Scientists are not entirely sure why the particles should have such inclinations, but they are fairly certain that the reason involves Enceladus.

One possible explanation is that all the E ring particles come from the plume of icy material that is shooting due south out of the moon's pole. This means all of the particles are created with a certain velocity out of the ringplane, and then they orbit above and below that plane.

Another possible explanation is that Enceladus produces particles with a range of speeds, but the moon gravitationally

PREFACE: Special section on vortex rings Special section on vortex rings

NASA Astrophysics Data System (ADS)

Fukumoto, Yasuhide

2009-10-01

This special section of Fluid Dynamics Research includes five articles on vortex rings in both classical and quantum fluids. The leading scientists of the field describe the trends in and the state-of-the-art development of experiments, theories and numerical simulations of vortex rings. The year 2008 was the 150th anniversary of 'vortex motion' since Hermann von Helmholtz opened up this field. In 1858, Helmholtz published a paper in Crelle's Journal which put forward the concept of 'vorticity' and made the first analysis of vortex motion. Fluid mechanics before that was limited to irrotational motion. In the absence of vorticity, the motion of an incompressible homogeneous fluid is virtually equivalent to a rigid-body motion in the sense that the fluid motion is determined once the boundary configuration is specified. Helmholtz proved, among other things, that, without viscosity, a vortex line is frozen into the fluid. This Helmholtz's law immediately implies the preservation of knots and links of vortex lines and its implication is enormous. One of the major trends of fluid mechanics since the latter half of the 20th century is to clarify the topological meaning of Helmholtz's law and to exploit it to develop theoretical and numerical methods to find the solutions of the Euler equations and to develop experimental techniques to gain an insight into fluid motion. Vortex rings are prominent coherent structures in a variety of fluid motions from the microscopic scale, through human and mesoscale to astrophysical scales, and have attracted people's interest. The late professor Philip G Saffman (1981) emphasized the significance of studies on vortex rings. One particular motion exemplifies the whole range of problems of vortex motion and is also a commonly known phenomenon, namely the vortex ring or smoke ring. Vortex rings are easily produced by dropping drops of one liquid into another, or by puffing fluid out of a hole, or by exhaling smoke if one has the skill

Surface roughness of Saturn's rings and ring particles inferred from thermal phase curves

NASA Astrophysics Data System (ADS)

Morishima, Ryuji; Turner, Neal J.; Spilker, Linda

2017-10-01

We analyze thermal phase curves of all the main rings of Saturn (the A, B, C rings, and the Cassini division) measured by both the far-IR and mid-IR detectors of the Cassini Composite InfraRed Spectrometer (CIRS). All the rings show temperature increases toward zero phase angle, known as an opposition effect or thermal beaming. For the C ring and Cassini division, which have low optical depths, intra-particle shadowing is considered the dominant mechanism causing the effect. On the other hand, the phase curves of the optically thick B and A rings steepen significantly with decreasing absolute solar elevation angle from 21° to 14°, suggesting inter-particle shadowing plays an important role in these rings. We employ an analytic roughness model to estimate the degrees of surface roughness of the rings or ring particles. For optically thin rings, an isolated particle covered by spherical segment craters is employed while for the thick rings we approximate a packed particle layer as a slab covered by craters. The particles in the thin rings are found to have generally rough surfaces, except in the middle C ring. Across the C ring, the optical depth correlates with the degree of surface roughness. This may indicate that surface roughness comes mainly from particle clumping, while individual particles have rather smooth surfaces. For the optically thick rings, the surface roughness of the particle layer is found to be moderate. The modeled phase curves of optically thick rings are shallow if the phase angle change is primarily due to change of observer azimuthal angle. On the other hand, the phase curves are steep if the phase angle change is due to change of observer elevation angle, as inter-particle shadows become visible at higher observer elevation. In addition, the area of shadowed facets increases with decreasing solar elevation angle. These combined effects explain the large seasonal change of the phase curve steepness observed for the thick rings. The degrees

Surface roughness of Saturn's rings and ring particles inferred from thermal phase curves

NASA Astrophysics Data System (ADS)

Morishima, Ryuji; Turner, Neal; Spilker, Linda

2017-10-01

We analyze thermal phase curves of all the main rings of Saturn (the A, B, C rings, and the Cassini division) measured by both the far-IR and mid-IR detectors of the Cassini Composite InfraRed Spectrometer (CIRS). All the rings show temperature increases toward zero phase angle, known as an opposition effect or thermal beaming. For the C ring and Cassini division, which have low optical depths, intra-particle shadowing is considered the dominant mechanism causing the effect. On the other hand, the phase curves of the optically thick B and A rings steepen significantly with decreasing absolute solar elevation angle from 21° to 14°, suggesting inter-particle shadowing plays an important role in these rings. We employ an analytic roughness model to estimate the degrees of surface roughness of the rings or ring particles. For optically thin rings, an isolated particle covered by spherical segment craters is employed while for the thick rings we approximate a packed particle layer as a slab covered by craters. The particles in the thin rings are found to have generally rough surfaces, except in the middle C ring. Across the C ring, the optical depth correlates with the degree of surface roughness. This may indicate that surface roughness comes mainly from particle clumping, while individual particles have rather smooth surfaces. For the optically thick rings, the surface roughness of the particle layer is found to be moderate. The modeled phase curves of optically thick rings are shallow if the phase angle change is primarily due to change of observer azimuthal angle. On the other hand, the phase curves are steep if the phase angle change is due to change of observer elevation angle, as inter-particle shadows become visible at higher observer elevation. In addition, the area of shadowed facets increases with decreasing solar elevation angle. These combined effects explain the large seasonal change of the phase curve steepness observed for the thick rings. The degrees

Dusty D Ring

NASA Image and Video Library

2014-02-24

Saturn D ring is easy to overlook since it trapped between the brighter C ring and the planet itself. In this view from NASA Cassini spacecraft, all that can be seen of the D ring is the faint and narrow arc as it stretches from top right of the ima

Ring World

NASA Image and Video Library

2007-03-01

Our robotic emissary, flying high above Saturn, captured this view of an alien copper-colored ring world. The overexposed planet has deliberately been removed to show the unlit rings alone, seen from an elevation of 60 degrees

Seismic performance of circular reinforced concrete bridge columns constructed with grade 80 reinforcement.

DOT National Transportation Integrated Search

2014-08-01

This project assessed the use of ASTM A706 Grade 80 reinforcing bars in reinforced concrete columns. : Grade 80 is not currently allowed in reinforced concrete columns due to lack of information on the : material characteristics and column performanc...

The prevalence of acetabular labral tears and associated pathology in a young asymptomatic population.

PubMed

Lee, A J J; Armour, P; Thind, D; Coates, M H; Kang, A C L

2015-05-01

Acetabular labral tears and associated intra-articular pathology of the hip have been recognised as a source of symptoms. However, it is now appreciated that there is a relatively high prevalence of asymptomatic labral tears. In this study, 70 young asymptomatic adult volunteers with a mean age of 26 years (19 to 41) were recruited and underwent three tesla non-arthrographic MR scans. There were 47 women (67.1%) and 23 men (32.9%). Labral tears were found in 27 volunteers (38.6%); these were an isolated finding in 16 (22.9%) and were associated with other intra-articular pathology in the remaining 11 (15.7%) volunteers. Furthermore, five (7.1%) had intra-articular pathology without an associated labral tear. Given the high prevalence of labral pathology in the asymptomatic population, it is important to confirm that a patient's symptoms are due to the demonstrated abnormalities when considering surgery. ©2015 The British Editorial Society of Bone & Joint Surgery.

Planetary rings: Structure and history

NASA Astrophysics Data System (ADS)

Esposito, L.

The composition and structure of planetary rings provide the key evidence to understand their origin and evolution. Before the first space observations, we were able to maintain an idealized view of the rings around Saturn, the only known ring system at that time. Rings were then discovered around Jupiter, Uranus and Neptune. Saturn's F ring was discovered by Pioneer 11. Our ideal view of circular, planar, symmetric and unchanging rings was shattered by observations of inclined, eccentric rings, waves and wavy edges, and numerous processes acting at rates that give timescales much younger than the solar system. Moons within and near the rings sculpt them and are the likely progenitors of future rings. The moonlet lifetimes are much less than Saturn's age. The old idea of ancient rings gave rise to youthful rings, that are recently created by erosion and destruction of small nearby moons. Although this explanation may work well for most rings, Saturn's massive ring system provides a problem. It is extremely improbable that Saturn's rings were recently created by the destruction of a moon as large as Mimas, or even by the breakup of a large comet that passed too close to Saturn. The history of Saturn's rings has been a difficult problem, now made even more challenging by the close-up Cassini measurements. Cassini observations show unexpected ring variability in time and space. Time variations are seen in ring edges, in the thinner D and F rings, and in the neutral oxygen cloud, which outweighs the E ring in the same region around Saturn. The rings are inhomogeneous, with structures on all scales, sharp gradients and edges. Compositional gradients are sharper than expected, but nonetheless cross structural boundaries. This is evidence for ballistic transport that has not gone to completion. The autocovariance maximizes in the middle of the A ring, with smaller structure near the main rings' outer edge. Density wave locations have a fresher ice composition. The

Ring King

NASA Image and Video Library

2014-08-18

Saturn reigns supreme, encircled by its retinue of rings. Although all four giant planets have ring systems, Saturn's is by far the most massive and impressive. Scientists are trying to understand why by studying how the rings have formed and how they have evolved over time. Also seen in this image is Saturn's famous north polar vortex and hexagon. This view looks toward the sunlit side of the rings from about 37 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on May 4, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers. The view was acquired at a distance of approximately 2 million miles (3 million kilometers) from Saturn. Image scale is 110 miles (180 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18278

Development of ductile hybrid fiber reinforced polymer (D-H-FRP) reinforcement for concrete structures

NASA Astrophysics Data System (ADS)

Somboonsong, Win

The corrosion of steel rebars has been the major cause of the reinforced concrete deterioration in transportation structures and port facilities. Currently, the Federal Highway Administration (FHWA) spends annually $31 billion for maintaining and repairing highways and highway bridges. The study reported herein represents the work done in developing a new type of reinforcement called Ductile Hybrid Fiber Reinforced Polymer or D-H-FRP using non-corrosive fiber materials. Unlike the previous FRP reinforcements that fail in a brittle manner, the D-H-FRP bars exhibit the stress-strain curves that are suitable for concrete reinforcement. The D-H-FRP stress-strain curves are linearly elastic with a definite yield point followed by plastic deformation and strain hardening resembling that of mild steel. In addition, the D-H-FRP reinforcement has integrated ribs required for concrete bond. The desirable mechanical properties of D-H-FRP reinforcement are obtained from the integrated design based on the material hybrid and geometric hybrid concepts. Using these concepts, the properties can be tailored to meet the specific design requirements. An analytical model was developed to predict the D-H-FRP stress-strain curves with different combination of fiber materials and geometric configuration. This model was used to optimize the design of D-H-FRP bars. An in-line braiding-pultrusion manufacturing process was developed at Drexel University to produce high quality D-H-FRP reinforcement in diameters that can be used in concrete structures. A series of experiments were carried out to test D-H-FRP reinforcement as well as their individual components in monotonic and cyclic tensile tests. Using the results from the tensile tests and fracture analysis, the stress-strain behavior of the D-H-FRP reinforcement was fully characterized and explained. Two series of concrete beams reinforced with D-H-FRP bars were studied. The D-H-FRP beam test results were then compared with companion

A Pauson-Khand and ring-expansion approach to the aquariane ring system.

PubMed

Thornton, Paul D; Burnell, D Jean

2006-07-20

[Structure: see text] The carbocyclic ring system of the aquariolide diterpenes has been synthesized by two routes involving a diastereoselective Pauson-Khand reaction and subsequent ring expansion. In one route, a tetracyclic enone was elaborated to generate the nine-membered ring by Grob fragmentation. In the second approach, a spirocyclic tricycle underwent a facile anionic oxy-Cope rearrangement to complete the synthesis of the desired ring system.

Effects of partial reinforcement and time between reinforced trials on terminal response rate in pigeon autoshaping.

PubMed

Gottlieb, Daniel A

2006-03-01

Partial reinforcement often leads to asymptotically higher rates of responding and number of trials with a response than does continuous reinforcement in pigeon autoshaping. However, comparisons typically involve a partial reinforcement schedule that differs from the continuous reinforcement schedule in both time between reinforced trials and probability of reinforcement. Two experiments examined the relative contributions of these two manipulations to asymptotic response rate. Results suggest that the greater responding previously seen with partial reinforcement is primarily due to differential probability of reinforcement and not differential time between reinforced trials. Further, once established, differences in responding are resistant to a change in stimulus and contingency. Secondary response theories of autoshaped responding (theories that posit additional response-augmenting or response-attenuating mechanisms specific to partial or continuous reinforcement) cannot fully accommodate the current body of data. It is suggested that researchers who study pigeon autoshaping train animals on a common task prior to training them under different conditions.

Bioinspired Interfacial Chelating-like Reinforcement Strategy toward Mechanically Enhanced Lamellar Materials.

PubMed

Chen, Ke; Zhang, Shuhao; Li, Anran; Tang, Xuke; Li, Lidong; Guo, Lin

2018-05-22

Many biological organisms usually derived from the ordered assembly of heterogeneous, hierarchical inorganic/organic constituents exhibit outstanding mechanical integration, but have proven to be difficult to produce the combination of excellent mechanical properties, such as strength, toughness, and light weight, by merely mimicking their component and structural characteristics. Herein, inspired by biologically strong chelating interactions of phytic acid (PA) or IP6 in many biomaterials, we present a biologically interfacial chelating-like reinforcement (BICR) strategy for fabrication of a highly dense ordered "brick-and-mortar" microstructure by incorporating tiny amounts of a natural chelating agent ( e. g., PA) into the interface or the interlamination of a material ( e. g., graphene oxide (GO)), which shows joint improvement in hardness (∼41.0%), strength (∼124.1%), maximum Young's modulus (∼134.7%), and toughness (∼118.5%) in the natural environment. Besides, for different composite matrix systems and artificial chelating agents, the BICR strategy has been proven successful for greatly enhancing their mechanical properties, which is superior to many previous reinforcing approaches. This point can be mainly attributed to the stronger noncovalent cross-linking interactions such as dense hydrogen bonds between the richer phosphate (hydroxyl) groups on its cyclohexanehexol ring and active sites of GO, giving rise to the larger energy dissipation at its hybrid interfaces. It is also simple and environmentally friendly for further scale-up fabrication and can be readily extended to other material systems, which opens an advanced reinforcement route to construct structural materials with high mechanical performance in an efficient way for practical applications.

O-Ring-Testing Fixture

NASA Technical Reports Server (NTRS)

Turner, James E.; Mccluney, D. Scott

1991-01-01

Fixture tests O-rings for sealing ability under dynamic conditions after extended periods of compression. Hydraulic cylinder moves plug in housing. Taper of 15 degrees on plug and cavity of housing ensures that gap created between O-ring under test and wall of cavity. Secondary O-rings above and below test ring maintain pressure applied to test ring. Evaluates effects of variety of parameters, including temperature, pressure, rate of pressurization, rate and magnitude of radial gap movement, and pretest compression time.

Nardo Ring, Italy

NASA Technical Reports Server (NTRS)

2008-01-01

The Nardo Ring is a striking visual feature from space, and astronauts have photographed it several times. The Ring is a race car test track; it is 12.5 kilometers long and steeply banked to reduce the amount of active steering needed by drivers. The Nardo Ring lies in a remote area on the heel of Italy's 'boot,' 50 kilometers east of the naval port of Taranto. The Ring encompasses a number of active (green) and fallow (brown to dark brown) agricultural fields. In this zone of intensive agriculture, farmers gain access to their fields through the Ring via a series of underpasses. Winding features within the southern section of the Ring appear to be smaller, unused race tracks.

The image covers an area of 18.8 x 16.4 km, was acquired on August 17. 2007, and is located at 49.3 degrees north latitude, 17.8 degrees east longitude.

The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

Correction of radiographic measurements of acetabular cup wear for variations in pelvis orientation.

PubMed

Derbyshire, Brian

2018-03-01

Radiographic measurement of two-dimensional acetabular cup wear is usually carried out on a series of follow-up radiographs of the patient's pelvis. Since the orientation of the pelvis might not be consistent at every X-ray examination, the resulting change in view of the wear plane introduces error into the linear wear measurement. This effect is amplified on some designs of cup in which the centre of the socket is several millimetres below the centre of the cup or circular wire marker. This study describes the formulation of a mathematical method to correct radiographic wear measurements for changes in pelvis orientation. A mathematical simulation of changes in cup orientation and wear vectors caused by pelvic tilt was used to confirm that the formulae corrected the wear exactly if the radiographic plane of the reference radiograph was parallel to the true plane of wear. An error analysis showed that even when the true wear plane was not parallel to the reference radiographic plane, the formulae could still provide a useful correction. A published correction formula was found to be ineffective.

Correction of radiographic measurements of acetabular cup wear for variations in pelvis orientation

PubMed Central

Derbyshire, Brian

2018-01-01

Radiographic measurement of two-dimensional acetabular cup wear is usually carried out on a series of follow-up radiographs of the patient’s pelvis. Since the orientation of the pelvis might not be consistent at every X-ray examination, the resulting change in view of the wear plane introduces error into the linear wear measurement. This effect is amplified on some designs of cup in which the centre of the socket is several millimetres below the centre of the cup or circular wire marker. This study describes the formulation of a mathematical method to correct radiographic wear measurements for changes in pelvis orientation. A mathematical simulation of changes in cup orientation and wear vectors caused by pelvic tilt was used to confirm that the formulae corrected the wear exactly if the radiographic plane of the reference radiograph was parallel to the true plane of wear. An error analysis showed that even when the true wear plane was not parallel to the reference radiographic plane, the formulae could still provide a useful correction. A published correction formula was found to be ineffective. PMID:29473454

Conditioned Reinforcement and Response Strength

PubMed Central

Shahan, Timothy A

2010-01-01

Stimuli associated with primary reinforcers appear themselves to acquire the capacity to strengthen behavior. This paper reviews research on the strengthening effects of conditioned reinforcers within the context of contemporary quantitative choice theories and behavioral momentum theory. Based partially on the finding that variations in parameters of conditioned reinforcement appear not to affect response strength as measured by resistance to change, long-standing assertions that conditioned reinforcers do not strengthen behavior in a reinforcement-like fashion are considered. A signposts or means-to-an-end account is explored and appears to provide a plausible alternative interpretation of the effects of stimuli associated with primary reinforcers. Related suggestions that primary reinforcers also might not have their effects via a strengthening process are explored and found to be worthy of serious consideration. PMID:20885815

[Laser Induced Fluorescence Spectroscopic Analysis of Aromatics from One Ring to Four Rings].

PubMed

Zhang, Peng; Liu, Hai-feng; Yue, Zong-yu; Chen, Bei-ling; Yao, Ming-fa

2015-06-01

In order to distinguish small aromatics preferably, a Nd : YAG Laser was used to supply an excitation laser, which was adjusted to 0.085 J x cm(-2) at 266 nm. Benzene, toluene, naphthalene, phenanthrene, anthracene, pyrene and chrysene were used as the representative of different rings aromatics. The fluorescence emission spectra were researched for each aromatic hydrocarbon and mixtures by Laser induced fluorescence (LIF). Results showed that the rings number determined the fluorescence emission spectra, and the structure with same rings number did not affect the emission fluorescence spectrum ranges. This was due to the fact that the absorption efficiency difference at 266 nm resulted in that the fluorescence intensities of each aromatic hydrocarbon with same rings number were different and the fluorescence intensities difference were more apparently with aromatic ring number increasing. When the absorption efficiency was similar at 266 nm and the concentrations of each aromatic hydrocarbon were same, the fluorescence intensities were increased with aromatic ring number increasing. With aromatic ring number increasing, the fluorescence spectrum and emission peak wavelength were all red-shifted from ultraviolet to visible and the fluorescence spectrum range was also wider as the absorption efficiency was similar. The fluorescence emission spectra from one to four rings could be discriminated in the following wavelengths, 275 to 320 nm, 320 to 375 nm, 375 to 425 nm, 425 to 556 nm, respectively. It can be used for distinguish the type of the polycyclic aromatic hydrocarbons (PAHs) as it exists in single type. As PAHs are usually exist in a variety of different rings number at the same time, the results for each aromatic hydrocarbon may not apply to the aromatic hydrocarbon mixtures. For the aromatic hydrocarbon mixtures, results showed that the one- or two-ring PAHs in mixtures could not be detected by fluorescence as three- or four-ring PAHs existed in mixture

Finite element modelling of concrete beams reinforced with hybrid fiber reinforced bars

NASA Astrophysics Data System (ADS)

Smring, Santa binti; Salleh, Norhafizah; Hamid, NoorAzlina Abdul; Majid, Masni A.

2017-11-01

Concrete is a heterogeneous composite material made up of cement, sand, coarse aggregate and water mixed in a desired proportion to obtain the required strength. Plain concrete does not with stand tension as compared to compression. In order to compensate this drawback steel reinforcement are provided in concrete. Now a day, for improving the properties of concrete and also to take up tension combination of steel and glass fibre-reinforced polymer (GFRP) bars promises favourable strength, serviceability, and durability. To verify its promise and support design concrete structures with hybrid type of reinforcement, this study have investigated the load-deflection behaviour of concrete beams reinforced with hybrid GFRP and steel bars by using ATENA software. Fourteen beams, including six control beams reinforced with only steel or only GFRP bars, were analysed. The ratio and the ordinate of GFRP to steel were the main parameters investigated. The behaviour of these beams was investigated via the load-deflection characteristics, cracking behaviour and mode of failure. Hybrid GFRP-Steel reinforced concrete beam showed the improvement in both ultimate capacity and deflection concomitant to the steel reinforced concrete beam. On the other hand, finite element (FE) modelling which is ATENA were validated with previous experiment and promising the good result to be used for further analyses and development in the field of present study.

Electrostatic forces in planetary rings

NASA Technical Reports Server (NTRS)

Goertz, C. K.; Shan, Linhua; Havnes, O.

1988-01-01

The average charge on a particle in a particle-plasma cloud, the plasma potential inside the cloud, and the Coulomb force acting on the particle are calculated. The net repulsive electrostatic force on a particle depends on the plasma density, temperature, density of particles, particle size, and the gradient of the particle density. In a uniformly dense ring the electrostatic repulsion is zero. It is also shown that the electrostatic force acts like a pressure force, that even a collisionless ring can be stable against gravitational collapse, and that a finite ring thickness does not necessarily imply a finite velocity dispersion. A simple criterion for the importance of electrostatic forces in planetary rings is derived which involves the calculation of the vertical ring thickness which would result if only electrostatic repulsion were responsible for the finite ring thickness. Electrostatic forces are entirely negligible in the main rings of Saturn and the E and G rings. They may also be negligible in the F ring. However, the Uranian rings and Jupiter's ring seem to be very much influenced by electrostatic repulsion. In fact, electrostatic forces could support a Jovian ring which is an order of magnitude more dense than observed.

Stirling engine piston ring

DOEpatents

Howarth, Roy B.

1983-01-01

A piston ring design for a Stirling engine wherein the contact pressure between the piston and the cylinder is maintained at a uniform level, independent of engine conditions through a balancing of the pressure exerted upon the ring's surface and thereby allowing the contact pressure on the ring to be predetermined through the use of a preloaded expander ring.

How does the blue-ringed octopus (Hapalochlaena lunulata) flash its blue rings?

PubMed

Mäthger, Lydia M; Bell, George R R; Kuzirian, Alan M; Allen, Justine J; Hanlon, Roger T

2012-11-01

The blue-ringed octopus (Hapalochlaena lunulata), one of the world's most venomous animals, has long captivated and endangered a large audience: children playing at the beach, divers turning over rocks, and biologists researching neurotoxins. These small animals spend much of their time in hiding, showing effective camouflage patterns. When disturbed, the octopus will flash around 60 iridescent blue rings and, when strongly harassed, bite and deliver a neurotoxin that can kill a human. Here, we describe the flashing mechanism and optical properties of these rings. The rings contain physiologically inert multilayer reflectors, arranged to reflect blue-green light in a broad viewing direction. Dark pigmented chromatophores are found beneath and around each ring to enhance contrast. No chromatophores are above the ring; this is unusual for cephalopods, which typically use chromatophores to cover or spectrally modify iridescence. The fast flashes are achieved using muscles under direct neural control. The ring is hidden by contraction of muscles above the iridophores; relaxation of these muscles and contraction of muscles outside the ring expose the iridescence. This mechanism of producing iridescent signals has not previously been reported in cephalopods and we suggest that it is an exceptionally effective way to create a fast and conspicuous warning display.

The Crossings of Saturn Ring Plane by the Earth in 1995: Ring Thickness

NASA Astrophysics Data System (ADS)

Poulet, François; Sicardy, Bruno; Dumas, Christophe; Jorda, Laurent; Tiphène, Didier

2000-05-01

The crossings of Saturn's ring plane by Earth were observed in the near infrared on May 22 and August 10, 1995, from the 2.2-m telescope of the University of Hawaii, the 2-m telescope at Pic du Midi, France, and with the Adonis adaptive optics camera at the 3.6-m telescope of the European Southern Observatory in Chile. Images from the Hubble Space Telescope, obtained in August 1995, are also reanalyzed. The radial brightness profiles of the rings indicate that the outer and usually faint F ring dominates the edge-on brightness of the system, thus hiding the vertical structure of the main rings within a few hours around the ring plane crossing. The photometric behaviors of the A, B, and C rings and of the Cassini Division are analyzed, using a radiative transfer code which includes the illuminations by the Sun and by the planet. The F ring is modeled as a physically thick ribbon of height H, composed of large particles embedded in dust of fractional optical depth f. The observed profiles, combined with previous results, can be explained if the F ring is both optically thick ( radial optical depth ˜0.20) and physically thick ( H=21±4 km). We suggest that this vertical distribution results from the interactions between ring particles and shepherding satellites and/or from gravitational stirring by large bodies. The dust particles dominate the F ring's photometric behavior even in backscattered light ( f>0.80). Constraints on the particle properties of the other rings are also derived.

Fiber reinforced engineering plastics

Treesearch

Daniel F. Caulfield; Rodney E. Jacobson; Karl D. Sears; John H. Underwood

2001-01-01

Although natural fiber reinforced commodity thermoplastics have a wide range of nonstructural applications in the automotive and decking industries, there have been few reports of cellulosic fiber-reinforced engineering thermoplastics. The commonly held belief has been that the only thermoplastics amenable to natural-fibre reinforcement are limited to low-melting (...

Luminescent Rings

NASA Technical Reports Server (NTRS)

2005-01-01

This view shows the unlit face of Saturn's rings, visible via scattered and transmitted light. In these views, dark regions represent gaps and areas of higher particle densities, while brighter regions are filled with less dense concentrations of ring particles.

The dim right side of the image contains nearly the entire C ring. The brighter region in the middle is the inner B ring, while the darkest part represents the dense outer B Ring. The Cassini Division and the innermost part of the A ring are at the upper-left.

Saturn's shadow carves a dark triangle out of the lower right corner of this image.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on June 8, 2005, at a distance of approximately 433,000 kilometers (269,000 miles) from Saturn. The image scale is 22 kilometers (14 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

A Photo-Favorskii Ring Contraction Reaction: The Effect of Ring Size

PubMed Central

Kammath, Viju Balachandran; Šolomek, Tomáš; Ngoy, Bokolombe Pitchou; Heger, Dominik; Klán, Petr; Rubina, Marina; Givens, Richard S.

2012-01-01

The effect of ring size on the photo-Favorskii induced ring-contraction reaction of the hydroxybenzocycloalkanonyl acetate and mesylate esters (7a–d, 8a–c) has provided new insight into the mechanism of the rearrangement. By monotonically decreasing the ring size in these cyclic derivatives, the increasing ring strain imposed on the formation of the elusive bicyclic spirocyclopropanone 20 results in a divergence away from rearrangement and toward solvolysis. Cycloalkanones of seven or eight carbons undergo a highly efficient photo-Favorskii rearrangement with ring contraction paralleling the photochemistry of p-hydroxyphenacyl esters. In contrast, the five-carbon ring does not rearrange but is diverted to the photosolvolysis channel avoiding the increased strain energy that would accompany the formation of the spirobicyclic ketone, the “Favorskii intermediate 20”. The six-carbon analogue demonstrates the bifurcation in reaction channels, yielding a solvent-sensitive mixture of both. Employing a combination of time-resolved absorption measurements, quantum yield determinations, isotopic labeling, and solvent variation studies coupled with theoretical treatment, a more comprehensive mechanistic description of the rearrangement has emerged. PMID:22686289

Earth: A Ringed Planet?

NASA Astrophysics Data System (ADS)

Hancock, L. O.; Povenmire, H.

2010-12-01

Among the most beautiful findings of the Space Age have been the discoveries of planetary rings. Not only Saturn but also Jupiter, Uranus and Neptune have rings; Saturn’s ring system has structures newly discovered; even Saturn's moon Rhea itself has a ring. All these are apparently supplied by material from the planetary moons (Rhea's ring by Rhea itself). The question naturally arises, why should the Earth not have a ring, and on the other hand, if it does, why has it not been observed? No rings have yet been observed in the inner solar system, but after all, rings in the inner solar system might simply tend to be fainter and more transient than those of the outer solar system: the inner solar system is more affected by the solar wind, and the Sun’s perturbing gravitational influence is greater. J.A. O’Keefe first suggested (1980) that Earth might have a ring system of its own. An Earth ring could account for some climate events. O’Keefe remarked that formation or thickening of a ring system in Earth’s equatorial plane could drive glaciation by deepening the chill of the winter hemisphere. (It is very well established that volcanic dust is an effective agent for the extinction of sunlight; this factor can be overwhelmingly apparent in eclipse observations.) O’Keefe died in 2000 and the speculation was not pursued, but the idea of an Earth ring has a prima facie reasonableness that calls for its renewed consideration. The program of this note is to hypothesize that, as O’Keefe proposed: (a) an Earth ring system exists; (b) it affects Earth's weather and climate; (c) the tektite strewn fields comprise filaments of the ring fallen to Earth's surface on various occasions of disturbance by comets or asteroids. On this basis, and drawing on the world's weather records, together with the Twentieth Century Reanalysis by NCEP/CIRES covering the period 1870-2010 and the geology of the tektite strewn fields, we herein propose the hypothesized Earth ring

BEHAVIORAL MECHANISMS UNDERLYING NICOTINE REINFORCEMENT

PubMed Central

Rupprecht, Laura E.; Smith, Tracy T.; Schassburger, Rachel L.; Buffalari, Deanne M.; Sved, Alan F.; Donny, Eric C.

2015-01-01

Cigarette smoking is the leading cause of preventable deaths worldwide and nicotine, the primary psychoactive constituent in tobacco, drives sustained use. The behavioral actions of nicotine are complex and extend well beyond the actions of the drug as a primary reinforcer. Stimuli that are consistently paired with nicotine can, through associative learning, take on reinforcing properties as conditioned stimuli. These conditioned stimuli can then impact the rate and probability of behavior and even function as conditioning reinforcers that maintain behavior in the absence of nicotine. Nicotine can also act as a conditioned stimulus, predicting the delivery of other reinforcers, which may allow nicotine to acquire value as a conditioned reinforcer. These associative effects, establishing non-nicotine stimuli as conditioned stimuli with discriminative stimulus and conditioned reinforcing properties as well as establishing nicotine as a conditioned stimulus, are predicted by basic conditioning principles. However, nicotine can also act non-associatively. Nicotine directly enhances the reinforcing efficacy of other reinforcing stimuli in the environment, an effect that does not require a temporal or predictive relationship between nicotine and either the stimulus or the behavior. Hence, the reinforcing actions of nicotine stem both from the primary reinforcing actions of the drug (and the subsequent associative learning effects) as well as the reinforcement enhancement action of nicotine which is non-associative in nature. Gaining a better understanding of how nicotine impacts behavior will allow for maximally effective tobacco control efforts aimed at reducing the harm associated with tobacco use by reducing and/or treating its addictiveness. PMID:25638333

Experimental investigation on bond of reinforcement in steel fibre-reinforced lightweight concrete

NASA Astrophysics Data System (ADS)

Holschemacher, K.; Ali, A.

2017-10-01

Bond behaviour of reinforcement is crucial parameter for load bearing reinforced concrete members. Many parameters like anchorage of reinforcement, lap splices, deflection or tension stiffening are influenced by the bond properties. It is well known that the ductility of bond can be improved by steel fibres. In this context almost innumerable experiments were performed for investigation of bond in normal weight concrete. However, the bond behaviour of reinforcement in steel fibre-reinforced lightweight concrete (SFRLWC) has received much less attention. For this reason, an experimental program dealing with bond in SFRLWC has been started at HTWK Leipzig/Germany. Main parts of the investigation were pull-out tests with various bar sizes and application of different steel fibre-reinforced lightweight and normal weight concretes. The paper reports the details of experimental investigations and evaluates the test results. As one of the most important outcomes that can be noted is that there is pronounced effect of bar size and steel fibre amount on bond properties in general. But those effects are more pronounced for SFRLWC in comparison to normal weight concrete with and without steel fibres.

Dynamics of the Uranian Rings

NASA Technical Reports Server (NTRS)

Dermott, S. F.

1984-01-01

Some of the problems of the shepherding satellite model of Goldreich ant tremaine are discussed. The following topics are studied: (1) optical depths of the all the observed narrow rings; (2) satellite and ring separation timescales; (3) ring edge sharpness; (4) shock formation in narrow rings; (5) the existence of small satellites near the Uranian rings; and (6) the apse and node alignments of the eccentric and inclined rings.

Self-Reinforcement Compared to Teacher-Delivered Reinforcement during Activity Schedules on the iPod Touch

ERIC Educational Resources Information Center

Beaver, Brittany N.; Reeve, Sharon A.; Reeve, Kenneth F.; DeBar, Ruth M.

2017-01-01

The current study assessed whether four 15- to 17-year-old individuals diagnosed with autism would remain on-task for more intervals and complete tasks independently as a function of using self-reinforcement or teacher-delivered reinforcement. An adapted alternating-treatments design with teacher-delivered reinforcement, self-reinforcement, and a…

Uranus rings and two moons

NASA Technical Reports Server (NTRS)

1986-01-01

Voyager 2 has discovered two 'shepherd' satellites associated with the rings of Uranus. The two moons -- designated 1986U7 and 1986U8 -- are seen here on either side of the bright epsilon ring; all nine of the known Uranian rings are visible. The image was taken Jan. 21, 1986, at a distance of 4.1 million kilometers (2.5 million miles) and resolution of about 36 km (22 mi). The image was processed to enhance narrow features. The epsilon ring appears surrounded by a dark halo as a result of this processing; occasional blips seen on the ring are also artifacts. Lying inward from the epsilon ring are the delta, gamma and eta rings; then the beta and alpha rings; and finally the barely visible 4, 5 and 6 rings. The rings have been studied since their discovery in 1977, through observations of how they diminish the light of stars they pass in front of. This image is the first direct observation of all nine rings in reflected sunlight. They range in width from about 100 km (60 mi) at the widest part of the epsilon ring to only a few kilometers for most of the others. The discovery of the two ring moons 1986U7 and 1986U8 is a major advance in our understanding of the structure of the Uranian rings and is in good agreement with theoretical predictions of how these narrow rings are kept from spreading out. Based on likely surface brightness properties, the moons are of roughly 2O- and 3O-km diameter, respectively. The Voyager project is managed for NASA by the Jet Propulsion Laboratory.

Methods for producing reinforced carbon nanotubes

DOEpatents

Ren, Zhifen [Newton, MA; Wen, Jian Guo [Newton, MA; Lao, Jing Y [Chestnut Hill, MA; Li, Wenzhi [Brookline, MA

2008-10-28

Methods for producing reinforced carbon nanotubes having a plurality of microparticulate carbide or oxide materials formed substantially on the surface of such reinforced carbon nanotubes composite materials are disclosed. In particular, the present invention provides reinforced carbon nanotubes (CNTs) having a plurality of boron carbide nanolumps formed substantially on a surface of the reinforced CNTs that provide a reinforcing effect on CNTs, enabling their use as effective reinforcing fillers for matrix materials to give high-strength composites. The present invention also provides methods for producing such carbide reinforced CNTs.

Tiny Mimas, Huge Rings

NASA Image and Video Library

2016-11-28

Saturn's icy moon Mimas is dwarfed by the planet's enormous rings. Because Mimas (near lower left) appears tiny by comparison, it might seem that the rings would be far more massive, but this is not the case. Scientists think the rings are no more than a few times as massive as Mimas, or perhaps just a fraction of Mimas' mass. Cassini is expected to determine the mass of Saturn's rings to within just a few hundredths of Mimas' mass as the mission winds down by tracking radio signals from the spacecraft as it flies close to the rings. The rings, which are made of small, icy particles spread over a vast area, are extremely thin -- generally no thicker than the height of a house. Thus, despite their giant proportions, the rings contain a surprisingly small amount of material. Mimas is 246 miles (396 kilometers) wide. This view looks toward the sunlit side of the rings from about 6 degrees above the ring plane. The image was taken in red light with the Cassini spacecraft wide-angle camera on July 21, 2016. The view was obtained at a distance of approximately 564,000 miles (907,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 31 degrees. Image scale is 34 miles (54 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20509

Retrofit of existing reinforced concrete bridges with fiber reinforced polymer composites

DOT National Transportation Integrated Search

2001-12-01

A two-part research was focused on examining various issues related to the use of fiber reinforced polymer (FRP) composites for strengthening of existing reinforced concrete bridges. A summary of each phase is presented separately.

Discrete element analysis is a valid method for computing joint contact stress in the hip before and after acetabular fracture.

PubMed

Townsend, Kevin C; Thomas-Aitken, Holly D; Rudert, M James; Kern, Andrew M; Willey, Michael C; Anderson, Donald D; Goetz, Jessica E

2018-01-23

Evaluation of abnormalities in joint contact stress that develop after inaccurate reduction of an acetabular fracture may provide a potential means for predicting the risk of developing post-traumatic osteoarthritis. Discrete element analysis (DEA) is a computational technique for calculating intra-articular contact stress distributions in a fraction of the time required to obtain the same information using the more commonly employed finite element analysis technique. The goal of this work was to validate the accuracy of DEA-computed contact stress against physical measurements of contact stress made in cadaveric hips using Tekscan sensors. Four static loading tests in a variety of poses from heel-strike to toe-off were performed in two different cadaveric hip specimens with the acetabulum intact and again with an intentionally malreduced posterior wall acetabular fracture. DEA-computed contact stress was compared on a point-by-point basis to stress measured from the physical experiments. There was good agreement between computed and measured contact stress over the entire contact area (correlation coefficients ranged from 0.88 to 0.99). DEA-computed peak contact stress was within an average of 0.5 MPa (range 0.2-0.8 MPa) of the Tekscan peak stress for intact hips, and within an average of 0.6 MPa (range 0-1.6 MPa) for fractured cases. DEA-computed contact areas were within an average of 33% of the Tekscan-measured areas (range: 1.4-60%). These results indicate that the DEA methodology is a valid method for accurately estimating contact stress in both intact and fractured hips. Copyright © 2017 Elsevier Ltd. All rights reserved.

On a suspected ring external to the visible rings of Saturn

NASA Technical Reports Server (NTRS)

Feibelman, W. A.; Beebe, R. F.; Smith, B. A.; Cook, A. F., II

1974-01-01

The reexamination of a photograph of Saturn taken on 15 November 1966 when the earth was nearly in the ring plane is investigated which indicates that ring material does exist outside the visible rings, extending to more than 6 Saturnian radii. The observed brightness in blue light was estimated per linear arc second, implying a normal optical thickness, for ice-covered particles.

Carbon Fiber Reinforced Polymer Grids for Shear and End Zone Reinforcement in Bridge Beams

DOT National Transportation Integrated Search

2018-01-01

Corrosion of reinforcing steel reduces life spans of bridges throughout the United States; therefore, using non-corroding carbon fiber reinforced polymer (CFRP) reinforcement is seen as a way to increase service life. The use of CFRP as the flexural ...

Deployable Fresnel Rings

NASA Technical Reports Server (NTRS)

Kennedy, Timothy F.; Fink, Patrick W.; Chu, Andrew W.; Lin, Gregory Y.

2014-01-01

Deployable Fresnel rings (DFRs) significantly enhance the realizable gain of an antenna. This innovation is intended to be used in combination with another antenna element, as the DFR itself acts as a focusing or microwave lens element for a primary antenna. This method is completely passive, and is also completely wireless in that it requires neither a cable, nor a connector from the antenna port of the primary antenna to the DFR. The technology improves upon the previous NASA technology called a Tri-Sector Deployable Array Antenna in at least three critical aspects. In contrast to the previous technology, this innovation requires no connector, cable, or other physical interface to the primary communication radio or sensor device. The achievable improvement in terms of antenna gain is significantly higher than has been achieved with the previous technology. Also, where previous embodiments of the Tri-Sector antenna have been constructed with combinations of conventional (e.g., printed circuit board) and conductive fabric materials, this innovation is realized using only conductive and non-conductive fabric (i.e., "e-textile") materials, with the possible exception of a spring-like deployment ring. Conceptually, a DFR operates by canceling the out-of-phase radiation at a plane by insertion of a conducting ring or rings of a specific size and distance from the source antenna, defined by Fresnel zones. Design of DFRs follow similar procedures to those outlined for conventional Fresnel zone rings. Gain enhancement using a single ring is verified experimentally and through computational simulation. The experimental test setup involves a microstrip patch antenna that is directly behind a single-ring DFR and is radiating towards a second microstrip patch antenna. The first patch antenna and DFR are shown. At 2.42 GHz, the DFR improves the transmit antenna gain by 8.6 dB, as shown in Figure 2, relative to the wireless link without the DFR. A figure illustrates the

Modifier 22 for acetabular fractures in morbidly obese patients: does it affect reimbursement?

PubMed

Bergin, Patrick F; Kneip, Christopher; Pierce, Christine; Hendrix, Stephen T; Porter, Scott E; Graves, Matthew L; Russell, George V

2014-11-01

Modifier 22 in the American Medical Association's Current Procedural Terminology (CPT®) book is a billing code for professional fees used to reflect an increased amount of skill, time, and work required to complete a procedure. There is little disagreement that using this code in the setting of surgery for acetabulum fractures in the obese patient is appropriate; however, to our knowledge, the degree to which payers value this additional level of complexity has not been determined. We asked whether (1) the use of Modifier 22 increased reimbursements in morbidly obese patients and (2) there was any difference between private insurance and governmental payer sources in treatment of Modifier 22. Over a 4-year period, we requested immediate adjudication with payers when using Modifier 22 for morbidly obese patients with acetabular fractures. We provided payers with evidence of the increased time and effort required in treating this population. Reimbursements were calculated for morbidly obese and nonmorbidly obese patients. Of the 346 patients we reviewed, 57 had additional CPT® codes or modifiers appended to their charges and were excluded, leaving 289 patients. Thirty (10%) were morbidly obese and were billed with Modifier 22. Fifty-three (18%) were insured by our largest private insurer and 69 (24%) by governmental programs (Medicare/Medicaid). Eight privately insured patients (15%) and seven governmentally insured patients (10%) were morbidly obese and were billed with Modifier 22. For our primary question, we compared reimbursement rates between patients with and without Modifier 22 for obesity within the 289 patients. We then performed the same comparison for the 53 privately insured patients and the 69 governmentally insured patients. Overall, there was no change in mean reimbursement when using Modifier 22 in morbidly obese patients, compared to nonmorbidly obese patients (USD 2126 versus USD 2149, p < 0.94). There was also no difference in mean

Ring rotational speed trend analysis by FEM approach in a Ring Rolling process

NASA Astrophysics Data System (ADS)

Allegri, G.; Giorleo, L.; Ceretti, E.

2018-05-01

Ring Rolling is an advanced local incremental forming technology to fabricate directly precise seamless ring-shape parts with various dimensions and materials. In this process two different deformations occur in order to reduce the width and the height of a preform hollow ring; as results a diameter expansion is obtained. In order to guarantee a uniform deformation, the preform is forced toward the Driver Roll whose aim is to transmit the rotation to the ring. The ring rotational speed selection is fundamental because the higher is the speed the higher will be the axial symmetry of the deformation process. However, it is important to underline that the rotational speed will affect not only the final ring geometry but also the loads and energy needed to produce it. Despite this importance in industrial environment, usually, a constant value for the Driver Roll angular velocity is set so to result in a decreasing trend law for the ring rotational speed. The main risk due to this approach is not fulfilling the axial symmetric constrain (due to the diameter expansion) and to generate a high localized ring section deformation. In order to improve the knowledge about this topic in the present paper three different ring rotational speed trends (constant, linearly increasing and linearly decreasing) were investigated by FEM approach. Results were compared in terms of geometrical and dimensional analysis, loads and energies required.

Full reinforcement operators in aggregation techniques.

PubMed

Yager, R R; Rybalov, A

1998-01-01

We introduce the concept of upward reinforcement in aggregation as one in which a collection of high scores can reinforce or corroborate each other to give an even higher score than any of the individual arguments. The concept of downward reinforcement is also introduced as one in which low scores reinforce each other. Our concern is with full reinforcement aggregation operators, those exhibiting both upward and downward reinforcement. It is shown that the t-norm and t-conorm operators are not full reinforcement operators. A class of operators called fixed identity MICA operators are shown to exhibit the property of full reinforcement. We present some families of these operators. We use the fuzzy system modeling technique to provide further examples of these operators.

Ring correlations in random networks.

PubMed

Sadjadi, Mahdi; Thorpe, M F

2016-12-01

We examine the correlations between rings in random network glasses in two dimensions as a function of their separation. Initially, we use the topological separation (measured by the number of intervening rings), but this leads to pseudo-long-range correlations due to a lack of topological charge neutrality in the shells surrounding a central ring. This effect is associated with the noncircular nature of the shells. It is, therefore, necessary to use the geometrical distance between ring centers. Hence we find a generalization of the Aboav-Weaire law out to larger distances, with the correlations between rings decaying away when two rings are more than about three rings apart.

Choice and conditioned reinforcement.

PubMed Central

Fantino, E; Freed, D; Preston, R A; Williams, W A

1991-01-01

A potential weakness of one formulation of delay-reduction theory is its failure to include a term for rate of conditioned reinforcement, that is, the rate at which the terminal-link stimuli occur in concurrent-chains schedules. The present studies assessed whether or not rate of conditioned reinforcement has an independent effect upon choice. Pigeons responded on either modified concurrent-chains schedules or on comparable concurrent-tandem schedules. The initial link was shortened on only one of two concurrent-chains schedules and on only one of two corresponding concurrent-tandem schedules. This manipulation increased rate of conditioned reinforcement sharply in the chain but not in the tandem schedule. According to a formulation of delay-reduction theory, when the outcomes chosen (the terminal links) are equal, as in Experiment 1, choice should depend only on rate of primary reinforcement; thus, choice should be equivalent for the tandem and chain schedules despite a large difference in rate of conditioned reinforcement. When the outcomes chosen are unequal, however, as in Experiment 2, choice should depend upon both rate of primary reinforcement and relative signaled delay reduction; thus, larger preferences should occur in the chain than in the tandem schedules. These predictions were confirmed, suggesting that increasing the rate of conditioned reinforcement on concurrent-chains schedules may have no independent effect on choice. PMID:2037826

Seal ring installation tool

NASA Technical Reports Server (NTRS)

Haselmaier, L. Haynes (Inventor)

2004-01-01

A seal ring tool that allows an installer to position a primary seal ring between hub ends of pipe flanges that are being assembled together. The tool includes a pivoting handle member and extension arms attached to the pivoting handle member. The ends of the arms have side indentation type longitudinal grooves angled toward one another for holding the primary seal ring in place between the hubs of respective pipes that are to be attached together. The arms of the tool can also have flat sides that can be used to abut against an optional second larger seal that is supported within a groove in one of the hub ends so that the second hub end can then be moved against the other side of the primary seal ring. Once the seal ring is positioned between the pipe hubs, the pipe hubs can be moved about the seal ring due to the flat sides of the arms of the tool. The tool eliminates the chances of damaging and contaminating seal rings being installed within pipe hubs that are being attached to one another.

3D printing utility for surgical treatment of acetabular fractures.

PubMed

Chana Rodríguez, F; Pérez Mañanes, R; Narbona Cárceles, F J; Gil Martínez, P

2018-05-25

Preoperative 3D modelling enables more effective diagnosis and simulates the surgical procedure. We report twenty cases of acetabular fractures with preoperative planning performed by pre-contouring synthesis plates on a 3D printed mould obtained from a computarized tomography (CT) scan. The mould impression was made with the DaVinci 1.0 printer model (XYZ Printing). After obtaining the printed hemipelvis, we proceeded to select the implant size (pelvic Matta system, Stryker ® ) that matched the characteristics of the fracture and the approach to be used. Printing the moulds took a mean of 385minutes (322-539), and 238grams of plastic were used to print the model (180-410). In all cases, anatomic reduction was obtained and intra-operative changes were not required in the initial contouring of the plates. The time needed to perform the full osteosynthesis, once the fracture had been reduced was 16.9minutes (10-24). In one case fixed with two plates, a postoperative CT scan showed partial contact of the implant with the surface of the quadrilateral plate. In the remaining cases, the contact was complete. In conclusion, our results suggest that the use of preoperative planning, by printing 3D mirror imaging models of the opposite hemipelvis and pre-contouring plates over the mould, might effectively achieve a predefined surgical objective and reduce the inherent risks in these difficult procedures. Copyright © 2018. Publicado por Elsevier España, S.L.U.

Neptune - full ring system

NASA Technical Reports Server (NTRS)

1989-01-01

This pair of Voyager 2 images (FDS 11446.21 and 11448.10), two 591-s exposures obtained through the clear filter of the wide angle camera, show the full ring system with the highest sensitivity. Visible in this figure are the bright, narrow N53 and N63 rings, the diffuse N42 ring, and (faintly) the plateau outside of the N53 ring (with its slight brightening near 57,500 km).

Barely Bisected Rings

NASA Image and Video Library

2016-09-12

Saturn's shadow stretched beyond the edge of its rings for many years after Cassini first arrived at Saturn, casting an ever-lengthening shadow that reached its maximum extent at the planet's 2009 equinox. This image captured the moment in 2015 when the shrinking shadow just barely reached across the entire main ring system. The shadow will continue to shrink until the planet's northern summer solstice, at which point it will once again start lengthening across the rings, reaching across them in 2019. Like Earth, Saturn is tilted on its axis. And, just as on Earth, as the sun climbs higher in the sky, shadows get shorter. The projection of the planet's shadow onto the rings shrinks and grows over the course of its 29-year-long orbit, as the angle of the sun changes with respect to Saturn's equator. This view looks toward the sunlit side of the rings from about 11 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Jan. 16, 2015. The view was obtained at a distance of approximately 1.6 million miles (2.5 million kilometers) from Saturn. Image scale is about 90 miles (150 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20498

Particle sizes in Saturn's rings from UVIS stellar occultations 1. Variations with ring region

NASA Astrophysics Data System (ADS)

Colwell, J. E.; Esposito, L. W.; Cooney, J. H.

2018-01-01

The Cassini spacecraft's Ultraviolet Imaging Spectrograph (UVIS) includes a high speed photometer (HSP) that has observed stellar occultations by Saturn's rings with a radial resolution of ∼10 m. In the absence of intervening ring material, the time series of measurements by the HSP is described by Poisson statistics in which the variance equals the mean. The finite sizes of the ring particles occulting the star lead to a variance that is larger than the mean due to correlations in the blocking of photons due to finite particle size and due to random variations in the number of individual particles in each measurement area. This effect was first exploited by Showalter and Nicholson (1990) with the stellar occultation observed by Voyager 2. At a given optical depth, a larger excess variance corresponds to larger particles or clumps that results in greater variation of the signal from measurement to measurement. Here we present analysis of the excess variance in occultations observed by Cassini UVIS. We observe differences in the best-fitting particle size in different ring regions. The C ring plateaus show a distinctly smaller effective particle size, R, than the background C ring, while the background C ring itself shows a positive correlation between R and optical depth. The innermost 700 km of the B ring has a distribution of excess variance with optical depth that is consistent with the C ring ramp and C ring but not with the remainder of the B1 region. The Cassini Division, while similar to the C ring in spectral and structural properties, has different trends in effective particle size with optical depth. There are discrete jumps in R on either side of the Cassini Division ramp, while the C ring ramp shows a smooth transition in R from the C ring to the B ring. The A ring is dominated by self-gravity wakes whose shadow size depends on the occultation geometry. The spectral ;halo; regions around the strongest density waves in the A ring correspond to

Measuring Acetabular Cup Orientation on Antero-Posterior Radiographs of the Hip after Total Hip Arthroplasty with a Vector Arithmetic Radiological Method. Is It Valid and Verified for Daily Clinical Practice?

PubMed

Craiovan, B; Weber, M; Worlicek, M; Schneider, M; Springorum, H R; Zeman, F; Grifka, J; Renkawitz, T

2016-06-01

The aim of this prospective study is to validate a vector arithmetic method for measuring acetabular cup orientation after total hip arthroplasty (THA) and to verify the clinical practice. We measured cup anteversion and inclination of 123 patients after cementless primary THA twice by two examiners on AP pelvic radiographs with a vector arithmetic method and compared with a 3D-CT based reconstruction model within the same radiographic coronal plane. The mean difference between the radiographic and the 3D-CT measurements was - 1.4° ± 3.9° for inclination and 0.8°± 7.9° for anteversion with excellent correlation for inclination (r = 0.81, p < 0.001) and moderate correlation for anteversion (r = 0.65, p < 0.001). The intraclass correlation coefficient for measurements on radiographs ranged from 0.98 (95 %-CI: 0.98; 0.99) for the first observer to 0.94 (95 %-CI: 0.92; 0.96) for the second observer. The interrater reliability was 0.96 (95 %-CI: 0.93; 0.98) for inclination and 0.93 (95 %-CI: 0.85; 0.96) for anteversion. The largest errors in measurements were associated with an extraordinary pelvic tilt. In order to get a valuable measurement for measuring cup position after THA on pelvic radiographs by this vector arithmetic method, there is a need for a correct postoperative ap view, with special regards to the pelvic tilt for the future. • Measuring acetabular cup orientation on anteroposterior radiographs of the hip after THA is a helpful procedure in everyday clinical practice as a first-line imaging modality• CT remains the golden standard to accurately determine acetabular cup position.• Future measuring on radiographs for cup orientation after THA should account for integration of the pelvic tilt in order to maximize the measurement accuracy. Citation Format: • Craiovan B, Weber M, Worlicek M et al. Measuring Acetabular Cup Orientation on Antero-Posterior Radiographs of the Hip after Total Hip Arthroplasty

The substitutability of reinforcers.

PubMed

Green, Leonard; Freed, Debra E

1993-07-01

Substitutability is a construct borrowed from microeconomics that describes a continuum of possible interactions among the reinforcers in a given situation. Highly substitutable reinforcers, which occupy one end of the continuum, are readily traded for each other due to their functional similarity. Complementary reinforcers, at the other end of the continuum, tend to be consumed jointly in fairly rigid proportion, and therefore cannot be traded for one another except to achieve that proportion. At the center of the continuum are reinforcers that are independent with respect to each other; consumption of one has no influence on consumption of another. Psychological research and analyses in terms of substitutability employ standard operant conditioning paradigms in which humans and nonhumans choose between alternative reinforcers. The range of reinforcer interactions found in these studies is more readily accommodated and predicted when behavior-analytic models of choice consider issues of substitutability. New insights are gained into such areas as eating and drinking, electrical brain stimulation, temporal separation of choice alternatives, behavior therapy, drug use, and addictions. Moreover, the generalized matching law (Baum, 1974) gains greater explanatory power and comprehensiveness when measures of substitutability are included.

The substitutability of reinforcers

PubMed Central

Green, Leonard; Freed, Debra E.

1993-01-01

Substitutability is a construct borrowed from microeconomics that describes a continuum of possible interactions among the reinforcers in a given situation. Highly substitutable reinforcers, which occupy one end of the continuum, are readily traded for each other due to their functional similarity. Complementary reinforcers, at the other end of the continuum, tend to be consumed jointly in fairly rigid proportion, and therefore cannot be traded for one another except to achieve that proportion. At the center of the continuum are reinforcers that are independent with respect to each other; consumption of one has no influence on consumption of another. Psychological research and analyses in terms of substitutability employ standard operant conditioning paradigms in which humans and nonhumans choose between alternative reinforcers. The range of reinforcer interactions found in these studies is more readily accommodated and predicted when behavior-analytic models of choice consider issues of substitutability. New insights are gained into such areas as eating and drinking, electrical brain stimulation, temporal separation of choice alternatives, behavior therapy, drug use, and addictions. Moreover, the generalized matching law (Baum, 1974) gains greater explanatory power and comprehensiveness when measures of substitutability are included. PMID:16812696

The 1995 Saturn Ring-Plane Crossings: Ring Thickness and Small Inner Satellites

NASA Astrophysics Data System (ADS)

Poulet, F.; Sicardy, B.

1996-09-01

The May 22() th and August 10() th, 1995, Saturn ring-plane crossings by the Earth were observed from the 2-m and 1-m telescopes at Pic du Midi, the 2.2-m telescope of the University of Hawaii, and with the Adonis adaptive optics camera at the 3.6-m telescope of the European Southern Observatory (ESO). Observations were made with either a 0.9 mu m or 2.2 mu m (short K) methane band filter. The radial brightness profiles of the rings indicate that the outer F ring dominates the apparent edge-on thickness of the system, with a vertically integrated equivalent width of 0.8-1.0 km near a radius of 130,000 km. The photometric behaviors of the A, B, and C rings and of the Cassini Division have been analyzed using a classical radiative transfer code which includes illumination by the Sun and by the planet. The F ring is modelled as a physically thick ribbon (thickness h) composed of large particles embedded in dust. The observed profiles can be explained if the F ring is both optically thick (tau ~ 0.15-0.25), and physically thick (h at least ~ 1.5 km). The large particles dominate the F ring's photometric behavior in backscattered light. Constraints on the particle properties in the other rings have been derived. The dimming of the rings around August 10, 1995 provided ideal conditions to study the small inner satellites. Besides Janus, Epimetheus and Pandora, two unresolved objects were detected in the ESO frames. They have been identified with the objects 1995S5 and 1995S6, detected several hours later by the Hubble Space Telescope (Nicholson et al. 1996, Science 272, 509--515). Combining the ESO and HST data, we derive orbital and photometric parameters for these objects. In particular, we improve the orbital parameters of 1995S5, whose orbital radius is now close to that of the F ring.

Saturn's dynamic D ring

USGS Publications Warehouse

Hedman, M.M.; Burns, J.A.; Showalter, M.R.; Porco, C.C.; Nicholson, P.D.; Bosh, A.S.; Tiscareno, M.S.; Brown, R.H.; Buratti, B.J.; Baines, K.H.; Clark, R.

2007-01-01

The Cassini spacecraft has provided the first clear images of the D ring since the Voyager missions. These observations show that the structure of the D ring has undergone significant changes over the last 25 years. The brightest of the three ringlets seen in the Voyager images (named D72), has transformed from a narrow, <40-km wide ringlet to a much broader and more diffuse 250-km wide feature. In addition, its center of light has shifted inwards by over 200 km relative to other features in the D ring. Cassini also finds that the locations of other narrow features in the D ring and the structure of the diffuse material in the D ring differ from those measured by Voyager. Furthermore, Cassini has detected additional ringlets and structures in the D ring that were not observed by Voyager. These include a sheet of material just interior to the inner edge of the C ring that is only observable at phase angles below about 60??. New photometric and spectroscopic data from the ISS (Imaging Science Subsystem) and VIMS (Visual and Infrared Mapping Spectrometer) instruments onboard Cassini show the D ring contains a variety of different particle populations with typical particle sizes ranging from 1 to 100 microns. High-resolution images reveal fine-scale structures in the D ring that appear to be variable in time and/or longitude. Particularly interesting is a remarkably regular, periodic structure with a wavelength of ??? 30 ?? km extending between orbital radii of 73,200 and 74,000 km. A similar structure was previously observed in 1995 during the occultation of the star GSC5249-01240, at which time it had a wavelength of ??? 60 ?? km. We interpret this structure as a periodic vertical corrugation in the D ring produced by differential nodal regression of an initially inclined ring. We speculate that this structure may have formed in response to an impact with a comet or meteoroid in early 1984. ?? 2006 Elsevier Inc. All rights reserved.

Formation of lunar basin rings

USGS Publications Warehouse

Hodges, C.A.; Wilhelms, D.E.

1978-01-01

The origin of the multiple concentric rings that characterize lunar impact basins, and the probable depth and diameter of the transient crater have been widely debated. As an alternative to prevailing "megaterrace" hypotheses, we propose that the outer scarps or mountain rings that delineate the topographic rims of basins-the Cordilleran at Orientale, the Apennine at Imbrium, and the Altai at Nectaris-define the transient cavities, enlarged relatively little by slumping, and thus are analogous to the rim crests of craters like Copernicus; inner rings are uplifted rims of craters nested within the transient cavity. The magnitude of slumping that occurs on all scarps is insufficient to produce major inner rings from the outer. These conclusions are based largely on the observed gradational sequence in lunar central uplifts:. from simple peaks through somewhat annular clusters of peaks, peak and ring combinations and double ring basins, culminating in multiring structures that may also include peaks. In contrast, belts of slump terraces are not gradational with inner rings. Terrestrial analogs suggest two possible mechanisms for producing rings. In some cases, peaks may expand into rings as material is ejected from their cores, as apparently occurred at Gosses Bluff, Australia. A second process, differential excavation of lithologically diverse layers, has produced nested experimental craters and is, we suspect, instrumental in the formation of terrestrial ringed impact craters. Peak expansion could produce double-ring structures in homogeneous materials, but differential excavation is probably required to produce multiring and peak-in-ring configurations in large lunar impact structures. Our interpretation of the representative lunar multiring basin Orientale is consistent with formation of three rings in three layers detected seismically in part of the Moon-the Cordillera (basin-bounding) ring in the upper crust, the composite Montes Rook ring in the underlying

Eyeing the E Ring

NASA Image and Video Library

2009-12-24

NASA Cassini spacecraft takes a look at Saturn diffuse E ring which is formed from icy material spewing out of the south pole of the moon Enceladus. The E ring is seen nearly edge-on from slightly above the northern side of Saturn ring plane.

Hot piston ring tests

NASA Technical Reports Server (NTRS)

Allen, David J.; Tomazic, William A.

1987-01-01

As part of the DOE/NASA Automotive Stirling Engine Project, tests were made at NASA Lewis Research Center to determine whether appendix gap losses could be reduced and Stirling engine performance increased by installing an additional piston ring near the top of each piston dome. An MTI-designed upgraded Mod I Automotive Stirling Engine was used. Unlike the conventional rings at the bottom of the piston, these hot rings operated in a high temperature environment (700 C). They were made of a high temperature alloy (Stellite 6B) and a high temperature solid lubricant coating (NASA Lewis-developed PS-200) was applied to the cylinder walls. Engine tests were run at 5, 10, and 15 MPa operating pressure over a range of operating speeds. Tests were run both with hot rings and without to provide a baseline for comparison. Minimum data to assess the potential of both the hot rings and high temperature low friction coating was obtained. Results indicated a slight increase in power and efficiency, an increase over and above the friction loss introduced by the hot rings. Seal leakage measurements showed a significant reduction. Wear on both rings and coating was low.

Tree Rings: Timekeepers of the Past.

ERIC Educational Resources Information Center

Phipps, R. L.; McGowan, J.

One of a series of general interest publications on science issues, this booklet describes the uses of tree rings in historical and biological recordkeeping. Separate sections cover the following topics: dating of tree rings, dating with tree rings, tree ring formation, tree ring identification, sample collections, tree ring cross dating, tree…

Cavity-locked ring down spectroscopy

DOEpatents

Zare, Richard N.; Paldus, Barbara A.; Harb, Charles C.; Spence, Thomas

2000-01-01

Distinct locking and sampling light beams are used in a cavity ring-down spectroscopy (CRDS) system to perform multiple ring-down measurements while the laser and ring-down cavity are continuously locked. The sampling and locking light beams have different frequencies, to ensure that the sampling and locking light are decoupled within the cavity. Preferably, the ring-down cavity is ring-shaped, the sampling light is s-polarized, and the locking light is p-polarized. Transmitted sampling light is used for ring-down measurements, while reflected locking light is used for locking in a Pound-Drever scheme.

Accidental ingestion of BiTine ring and a note on inefficient ring separation forceps.

PubMed

Baghele, Om Nemichand; Baghele, Mangala Om

2011-01-01

Accidental ingestion of medium-to-large instruments is relatively uncommon during dental treatment but can be potentially dangerous. A case of BiTine ring ingestion is presented with a note on inefficient ring separation forceps. A 28-year-old male patient accidentally ingested the BiTine ring (2 cm diameter, 0.5 cm outward projections) while it was being applied to a distoproximal cavity in tooth # 19. The ring placement forceps were excessively flexible; bending of the beaks towards the ring combined with a poor no-slippage mechanism led to sudden disengagement of the ring and accelerated movement towards the pharynx. We followed the patient with bulk forming agents and radiographs. Fortunately the ring passed out without any complications. Checking equipment and methods is as important as taking precautions against any preventable medical emergency. It is the responsibility of the clinician to check, verify and then use any instrument/equipment.

Inspection and evaluation of a bridge deck reinforced with carbon fiber reinforced polymer (CFRP) bars.

DOT National Transportation Integrated Search

2006-03-01

Cracking in reinforced concrete decks is inevitable. It leads to the corrosion and eventual deterioration of the deck system. The use of non-corrosive reinforcement is one alternative to steel in reinforced concrete construction. : This report deals ...

Health monitoring of precast bridge deck panels reinforced with glass fiber reinforced polymer (GFRP) bars.

DOT National Transportation Integrated Search

2012-03-01

The present research project investigates monitoring concrete precast panels for bridge decks that are reinforced with Glass Fiber Reinforced Polymer (GFRP) bars. Due to the lack of long term research on concrete members reinforced with GFRP bars, lo...

Dynamic and static strength of an implant-supported overdenture model reinforced with metal and nonmetal strengtheners.

PubMed

Rached, Rodrigo Nunes; de Souza, Evelise Machado; Dyer, Scott R; Ferracane, Jack Liborio

2011-11-01

Fractures of overdentures occur in the denture base through the abutments. The purpose of this study was to evaluate the effect of reinforcements and the space available for their placement on the dynamic and static loading capacity of a simulated implant-supported overdenture model. Rhomboidal (6 × 6 × 25 mm) test specimens (n=8), made with an acrylic resin and containing 2 metal O-ring capsules, were reinforced with braided stainless steel bar (BS), stainless steel mesh (SM), unidirectional E-glass fiber (GF), E-glass mesh (GM), woven polyethylene braids (PE), or polyaramid fibers (PA). Two distinct spaces for reinforcement placement were investigated: a 2.5 mm and a 1 mm space. Control groups consisted of nonreinforced specimens. Specimens were thermocycled (5°C and 55°C, 5,000 cycles) and then subjected to a 100,000 cyclic load regime. Unbroken specimens were then loaded until failure. The number of failures under fatigue (f) and static load (s) were compared with the Chi-Square test, while static load means were compared with the Kruskal-Wallis test (α=.05). The number of failures (f:s) of GF (0:16), PE (0:16), and PA (0:16) differed significantly from the control group (8:8) and SM (4:12) (P=.037 and P=.025, respectively). For the 2.5 mm space group, these same reinforcements also exhibited higher static load means than the control (P=.016, P=.003, and P=.003, respectively); under static load, no significant differences were detected between the reinforced groups and the control for the 1.0 mm space group (P=1.0). E-glass fibers, woven polyethylene braids, and polyaramid fibers withstood the fatigue regime and increased the flexural strength of the implant-supported overdenture model. The spaces available for reinforcement did not affect the dynamic strength or the static loading capacity of the implant-supported overdenture model. Copyright © 2011 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

Photometry of Polar-Ring Galaxies

NASA Astrophysics Data System (ADS)

Godínez-Martínez, A.; Watson, A. M.; Matthews, L. D.; Sparke, L. S.

2007-10-01

We have obtained photometry in B and R for seven confirmed or probable polar-ring galaxies from the Polar-Ring Catalog of Whitmore et al. (1990). The rings show a range of colors from B - R ≈ 0.6 to B - R ≈ 1.7. The bluest rings have bright H II regions, which are direct evidence for recent star formation. The minimum age of the reddest ring, that in PRC B-20, is somewhat uncertain because of a lack of knowledge of the internal reddening and metallicity, but appears to be at least 1.2 Gyr. As such, this ring is likely to be stable for at least several rotation periods. This ring is an excellent candidate for future studies that might better determine if it is truly old.

Corrosion control for reinforced concrete

NASA Astrophysics Data System (ADS)

Torigoe, R. M.

The National Bureau of Standards has recorded that in 1975 the national cost of corrosion was estimated at $70 billion. Approximately 40% of that total was attributed to the corrosion of steel reinforcements in concrete. Though concrete is generally perceived as a permanent construction material, cracking and spalling can occur when corrosion of steel reinforcements progresses to an advanced stage. This problem frequently occurs in reinforced concrete highway bridge decks, wharves, piers, and other structures in marine and snowbelt environments. Since concrete has a very low tensile strength, steel reinforcements are added to carry the tensile load of the composite member. Corrosion reduces the effective diameter of the reinforcements and, therefore, decreases the load carrying capability of the member. Though the corrosion process may occur in various forms and may be caused by different sources, the ultimate result is still the failure of the reinforced concrete.

The nature of sexual reinforcement.

PubMed Central

Crawford, L L; Holloway, K S; Domjan, M

1993-01-01

Sexual reinforcers are not part of a regulatory system involved in the maintenance of critical metabolic processes, they differ for males and females, they differ as a function of species and mating system, and they show ontogenetic and seasonal changes related to endocrine conditions. Exposure to a member of the opposite sex without copulation can be sufficient for sexual reinforcement. However, copulatory access is a stronger reinforcer, and copulatory opportunity can serve to enhance the reinforcing efficacy of stimulus features of a sexual partner. Conversely, under certain conditions, noncopulatory exposure serves to decrease reinforcer efficacy. Many common learning phenomena such as acquisition, extinction, discrimination learning, second-order conditioning, and latent inhibition have been demonstrated in sexual conditioning. These observations extend the generality of findings obtained with more conventional reinforcers, but the mechanisms of these effects and their gender and species specificity remain to be explored. PMID:8354970

Improving the Accuracy of Laplacian Estimation with Novel Variable Inter-Ring Distances Concentric Ring Electrodes

PubMed Central

Makeyev, Oleksandr; Besio, Walter G.

2016-01-01

Noninvasive concentric ring electrodes are a promising alternative to conventional disc electrodes. Currently, the superiority of tripolar concentric ring electrodes over disc electrodes, in particular, in accuracy of Laplacian estimation, has been demonstrated in a range of applications. In our recent work, we have shown that accuracy of Laplacian estimation can be improved with multipolar concentric ring electrodes using a general approach to estimation of the Laplacian for an (n + 1)-polar electrode with n rings using the (4n + 1)-point method for n ≥ 2. This paper takes the next step toward further improving the Laplacian estimate by proposing novel variable inter-ring distances concentric ring electrodes. Derived using a modified (4n + 1)-point method, linearly increasing and decreasing inter-ring distances tripolar (n = 2) and quadripolar (n = 3) electrode configurations are compared to their constant inter-ring distances counterparts. Finite element method modeling and analytic results are consistent and suggest that increasing inter-ring distances electrode configurations may decrease the truncation error resulting in more accurate Laplacian estimates compared to respective constant inter-ring distances configurations. For currently used tripolar electrode configuration, the truncation error may be decreased more than two-fold, while for the quadripolar configuration more than a six-fold decrease is expected. PMID:27294933

Improving the Accuracy of Laplacian Estimation with Novel Variable Inter-Ring Distances Concentric Ring Electrodes.

PubMed

Makeyev, Oleksandr; Besio, Walter G

2016-06-10

Noninvasive concentric ring electrodes are a promising alternative to conventional disc electrodes. Currently, the superiority of tripolar concentric ring electrodes over disc electrodes, in particular, in accuracy of Laplacian estimation, has been demonstrated in a range of applications. In our recent work, we have shown that accuracy of Laplacian estimation can be improved with multipolar concentric ring electrodes using a general approach to estimation of the Laplacian for an (n + 1)-polar electrode with n rings using the (4n + 1)-point method for n ≥ 2. This paper takes the next step toward further improving the Laplacian estimate by proposing novel variable inter-ring distances concentric ring electrodes. Derived using a modified (4n + 1)-point method, linearly increasing and decreasing inter-ring distances tripolar (n = 2) and quadripolar (n = 3) electrode configurations are compared to their constant inter-ring distances counterparts. Finite element method modeling and analytic results are consistent and suggest that increasing inter-ring distances electrode configurations may decrease the truncation error resulting in more accurate Laplacian estimates compared to respective constant inter-ring distances configurations. For currently used tripolar electrode configuration, the truncation error may be decreased more than two-fold, while for the quadripolar configuration more than a six-fold decrease is expected.

Embryonic ring closure: Actomyosin rings do the two-step

PubMed Central

2016-01-01

Actomyosin rings drive numerous closure processes, but the mechanisms by which they contract are still poorly understood. In this issue, Xue and Sokac (2016. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201608025) show that actomyosin ring closure during Drosophila melanogaster cellularization uses two steps, only one of which involves Myosin-2. PMID:27799371

Caregiver preference for reinforcement-based interventions for problem behavior maintained by positive reinforcement.

PubMed

Gabor, Anne M; Fritz, Jennifer N; Roath, Christopher T; Rothe, Brittany R; Gourley, Denise A

2016-06-01

Social validity of behavioral interventions typically is assessed with indirect methods or by determining preferences of the individuals who receive treatment, and direct observation of caregiver preference rarely is described. In this study, preferences of 5 caregivers were determined via a concurrent-chains procedure. Caregivers were neurotypical, and children had been diagnosed with developmental disabilities and engaged in problem behavior maintained by positive reinforcement. Caregivers were taught to implement noncontingent reinforcement (NCR), differential reinforcement of alternative behavior (DRA), and differential reinforcement of other behavior (DRO), and the caregivers selected interventions to implement during sessions with the child after they had demonstrated proficiency in implementing the interventions. Three caregivers preferred DRA, 1 caregiver preferred differential reinforcement procedures, and 1 caregiver did not exhibit a preference. Direct observation of implementation in concurrent-chains procedures may allow the identification of interventions that are implemented with sufficient integrity and preferred by caregivers. © 2016 Society for the Experimental Analysis of Behavior.

Scintillating C Ring

NASA Image and Video Library

2007-01-16

Both luminous and translucent, the C ring sweeps out of the darkness of Saturn's shadow and obscures the planet at lower left. The ring is characterized by broad, isolated bright areas, or "plateaus," surrounded by fainter material. This view looks toward the unlit side of the rings from about 19 degrees above the ringplane. North on Saturn is up. The dark, inner B ring is seen at lower right. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Dec. 15, 2006 at a distance of approximately 632,000 kilometers (393,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 56 degrees. Image scale is 34 kilometers (21 miles) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA08855

Radar imaging of Saturn's rings

NASA Astrophysics Data System (ADS)

Nicholson, Philip D.; French, Richard G.; Campbell, Donald B.; Margot, Jean-Luc; Nolan, Michael C.; Black, Gregory J.; Salo, Heikki J.

2005-09-01

We present delay-Doppler images of Saturn's rings based on radar observations made at Arecibo Observatory between 1999 and 2003, at a wavelength of 12.6 cm and at ring opening angles of 20.1°⩽|B|⩽26.7°. The average radar cross-section of the A ring is ˜77% relative to that of the B ring, while a stringent upper limit of 3% is placed on the cross-section of the C ring and 9% on that of the Cassini Division. These results are consistent with those obtained by Ostro et al. [1982, Icarus 49, 367-381] from radar observations at |B|=21.4°, but provide higher resolution maps of the rings' reflectivity profile. The average cross-section of the A and B rings, normalized by their projected unblocked area, is found to have decreased from 1.25±0.31 to 0.74±0.19 as the rings have opened up, while the circular polarization ratio has increased from 0.64±0.06 to 0.77±0.06. The steep decrease in cross-section is at variance with previous radar measurements [Ostro et al., 1980, Icarus 41, 381-388], and neither this nor the polarization variations are easily understood within the framework of either classical, many-particle-thick or monolayer ring models. One possible explanation involves vertical size segregation in the rings, whereby observations at larger elevation angles which see deeper into the rings preferentially see the larger particles concentrated near the rings' mid-plane. These larger particles may be less reflective and/or rougher and thus more depolarizing than the smaller ones. Images from all four years show a strong m=2 azimuthal asymmetry in the reflectivity of the A ring, with an amplitude of ±20% and minima at longitudes of 67±4° and 247±4° from the sub-Earth point. We attribute the asymmetry to the presence of gravitational wakes in the A ring as invoked by Colombo et al. [1976, Nature 264, 344-345] to explain the similar asymmetry long seen at optical wavelengths. A simple radiative transfer model suggests that the enhancement of the azimuthal

Aggression as Positive Reinforcement in Mice under Various Ratio- and Time-Based Reinforcement Schedules

ERIC Educational Resources Information Center

May, Michael E.; Kennedy, Craig H.

2009-01-01

There is evidence suggesting aggression may be a positive reinforcer in many species. However, only a few studies have examined the characteristics of aggression as a positive reinforcer in mice. Four types of reinforcement schedules were examined in the current experiment using male Swiss CFW albino mice in a resident-intruder model of aggression…

Effects of reinforcer magnitude on responding under differential-reinforcement-of-low-rate schedules of rats and pigeons.

PubMed

Doughty, Adam H; Richards, Jerry B

2002-07-01

Experiment I investigated the effects of reinforcer magnitude on differential-reinforcement-of-low-rate (DRL) schedule performance in three phases. In Phase 1, two groups of rats (n = 6 and 5) responded under a DRI. 72-s schedule with reinforcer magnitudes of either 30 or 300 microl of water. After acquisition, the water amounts were reversed for each rat. In Phase 2, the effects of the same reinforcer magnitudes on DRL 18-s schedule performance were examined across conditions. In Phase 3, each rat responded unider a DR1. 18-s schedule in which the water amotnts alternated between 30 and 300 microl daily. Throughout each phase of Experiment 1, the larger reinforcer magnitude resulted in higher response rates and lower reinforcement rates. The peak of the interresponse-time distributions was at a lower value tinder the larger reinforcer magnitude. In Experiment 2, 3 pigeons responded under a DRL 20-s schedule in which reinforcer magnitude (1-s or 6-s access to grain) varied iron session to session. Higher response rates and lower reinforcement rates occurred tinder the longer hopper duration. These results demonstrate that larger reinforcer magnitudes engender less efficient DRL schedule performance in both rats and pigeons, and when reinforcer magnitude was held constant between sessions or was varied daily. The present results are consistent with previous research demonstrating a decrease in efficiency as a function of increased reinforcer magnituide tinder procedures that require a period of time without a specified response. These findings also support the claim that DRI. schedule performance is not governed solely by a timing process.

Uranus Rings in False Color

NASA Technical Reports Server (NTRS)

1986-01-01

This false-color view of the rings of Uranus was made from images taken by Voyager 2 on Jan. 21, 1986, from a distance of 4.17 million kilometers (2.59 million miles). All nine known rings are visible here; the somewhat fainter, pastel lines seen between them are contributed by the computer enhancement. Six 15-second narrow-angle images were used to extract color information from the extremely dark and faint rings. Two images each in the green, clear and violet filters were added together and averaged to find the proper color differences between the rings. The final image was made from these three color averages and represents an enhanced, false-color view. The image shows that the brightest, or epsilon, ring at top is neutral in color, with the fainter eight other rings showing color differences between them. Moving down, toward Uranus, we see the delta, gamma and eta rings in shades of blue and green; the beta and alpha rings in somewhat lighter tones; and then a final set of three, known simply as the 4, 5 and 6 rings, in faint off-white tones. Scientists will use this color information to try to understand the nature and origin of the ring material. The resolution of this image is approximately 40 km (25 mi). The Voyager project is managed for NASA by the Jet Propulsion Laboratory.

Deformation of the Durom Acetabular Component and Its Impact on Tribology in a Cadaveric Model—A Simulator Study