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The mal-positioning of total hip arthroplasty components can result in edge loading conditions. Purpose of this study was to determine if the wear rate of ceramic-on-ceramic and metal-on-polyethylene increases under edge loading conditions. The literature was reviewed to determine which of the commonly used hip bearings is the most forgiving to implant mal-orientation. Two 28-mm ceramic-on-ceramic articulations were tested in vitro: pure alumina (PAL) ceramic versus the new alumina-toughened zirconia (ATZ). Two 28-mm metal-on-polyethylene articulations were tested in vitro: conventional ultrahigh molecular weight polyethylene (UHMWPE) versus highly crosslinked polyethylene (HXLPE) stabilized with vitamin E. All bearings were tested at standard and at highest possible inclination angles. Hip simulator tests were run for five million cycles based on N = 3 tests per condition. The average wear rate of ATZ-on-ATZ is 0.024 mm(3) /Mcycles at 45° and 0.018 mm(3) /Mcycles at 65°. Wear rate of PAL-on-PAL is between 0.02 and 0.03 mm(3) /Mcycles at 45°, as well as 65°. The wear rate of UHMWPE was 31 ± 1 mm(3) /Mcycles at an inclination angle of 45° and 26 ± 1 mm(3) /Mcycles at 80°. The wear rate of vitamin E stabilized HXLPE was 5.9 ± 0.2 mm(3) /Mcycles at 45° and 5.8 ± 0.2 mm(3) /Mcycles at 80°. Edge loading does not increase the wear rate of ceramic-on-ceramic and metal-on-polyethylene articulations. The newest biomaterials showed markedly lower wear rates compared with their conventional counterparts. ATZ-on-ATZ showed the lowest wear rate of all tested pairings, but the vitamin E stabilized HXLPE seems to be the most forgiving material when it comes to implant mal-orientation.

Background Monoblock acetabular components used in uncemented total hip arthroplasty (THA) have certain mechanical characteristics that potentially reduce acetabular osteolysis and polyethylene wear. However, the degree to which they achieve this goal is not well documented. Questions/purposes The purpose of this study was to use a systematic review of controlled trials to test the hypothesis that monoblock cups have superior (1) polyethylene wear rate; (2) frequency of cup migration; (3) frequency of acetabular osteolysis; and (4) frequency of aseptic loosening compared with modular components used in uncemented THA.Methods A systematic search was conducted in the Medline, Embase, and Cochrane electronic databases to assemble all controlled trials comparing monoblock with modular uncemented acetabular components in primary THA. Included studies were considered ''best evidence'' if the quality score was either C 50% on the Cochrane Back Review Group checklist or C 75% the Newcastle-Ottawa quality assessment scale. A total of seven publications met our inclusion criteria. Results Best evidence analysis showed no difference in polyethylene wear rate, the frequency of cup migration, and aseptic loosening between monoblock and modular acetabular components. No convincing evidence was found for the claim that lower frequencies of acetabular osteolysis are observed with the use of monoblock cups compared with modular uncemented cups. Conclusions The purported benefits of monoblock cups were not substantiated by this systematic review of controlled studies in that polyethylene wear rates and frequencies of cup failure and acetabular osteolysis were similar to those observed with modular implants. Other factors should therefore drive implant selection in cementless THA. Level of Evidence Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

IntroductionDifferences between radiologists and orthopaedic surgeons in the interpretation of MR images of the shoulder joint are experienced in daily clinical practice. This study set out to evaluate the inter-observer agreement between radiologists and orthopaedic surgeons in assessing pathology on MR imaging of the shoulder joint. Also, we determined the accuracy of the observers with arthroscopy as the standard of reference.Materials and methodsTwo radiologists and one orthopaedic surgeon reviewed 50 MR studies—25 conventional MR examinations and 25 MR arthrographies—of patients with shoulder complaints who had undergone MR imaging and subsequently arthroscopic surgery. The assessment was independent and blinded. All observers evaluated the MR examinations twice. Standard evaluation forms were used to score for pathology of rotator cuff, glenoid labrum, tendon of the long head of the biceps brachii and glenohumeral ligaments. The presence or absence of osteoarthritis, SLAP lesions, Bankart lesions, Hill-Sachs lesions or impingement was also noted. Intra- and inter-observer agreement, the sensitivity and specificity were calculated. Differences in percentages of correctly diagnosed lesions were tested for significance using McNemar’s test.ResultsThere was a poor inter-observer agreement between the orthopaedic surgeon and the radiologists in assessing Bankart lesions and ligamentous lesions. We found significant differences between the radiologists and the orthopaedic surgeon in the assessment of osteoarthritis, Hill-Sachs lesions and impingement.ConclusionThe orthopaedic surgeon and radiologists differed in their interpretation of what defines a Bankart lesion and what defines a ligamentous lesion. The orthopaedic surgeon was significantly more accurate in assessing impingement.