Introduction: The debris of standard Polyethylene in Total Hip Arthroplasty (THA) has been responsible for aseptic loosing and osteolysis in many patients. Wear rates for Polyethylene-Ceramic are analysed around 10 to 20 mm3 per year, those of PE-metal even 5 times more. Dislocation of primary THA is also common and problematic. Using a PE insert with a dorsal rim lowers the risk of dislocation but could be a potential risk for impingement if not correctly placed. Aim of this study was to value of reduced risk for dislocation in terms of increased risk for impingements. Study design: Between 1989 and 2003, 1107 non-cemented SL cups with Polyethylene on Ceramic were implanted in 953 patients, 422 (44%) implanted in women. All PE inserts were with dorsal rim. Average age at implantation was 69.9 years (range 39 to 90). In all cases, a cemented stem was implanted. Of those 1107 primary THA, 100 were revised for aseptic loosening. In 11 cases both components were revised, 7 times only the cup was replaced and for the 82 revisions remaining, only the stem was revised. In all cases the PE insert was removed and replaced. All inserts were analysed macroscopically for impingement and the volume worn off was calculated. Dislocation risk of PE couplings with rim was compared to standard PE couplings without rim. Results: In 18 PE inserts of 100 with rim, signs of impingement were found, ranging from slight (considered as creep not wear) to massive. An average yearly wear rate of 43 mm^3 (range 7 to 119) was calculated. Median survival time of the inserts without impingement was 5.2 years (range 0.7 to 11.4) of those with impingement it was reduced to 4.5 years (range 1.1 to 13.8). No statistical difference calculated (Mann-Whitney-U test, p=0.28) . In 2 of all 1107 cases (0.2%) operative revision of dislocation was performed whereas in 6 of the 598 cases (1%) with PE cups without rim, operative intervention was performed. Discussion: The use of a PE insert with dislocation protection rim holds a potential danger if not correctly placed. Though an earlier failing of THA with PE impingement was found, it was not significant and overpowered by the fact that most loosenings were due to cemented titanium stems with their great potential for early loosening.

Introduction: Polyethylene wear is an important factor for the longevity of total knee arthroplasty (TKA). One would expect that TKA lasting till death shows no or minimal wear compared to TKA undergoing revision surgery.

Material and Method: The present study retrospectively looks at the amount of front side wear on tibial retrievals and correlates clinical and radiological data sampled from these patients’ medical records. All Prostheses are of the same type and company (Stryker Howmedica, Allendale) with the following distribution: PCA 16, PCA modular 19 and Duracon 5. All inserts were gamma sterilized on air. Mean implantation time and mean age at implantation was 100.1 ±55.8 month and 70.7 ±7.4 years respectively. A modified visual score first described by Hood et al. 1983 served as measure for total damage on the polyethylene surface. Statistical Analysis was done by univariate analysis of variance.

Results: A highly significant influence on wear was found for the following factors: time of implantation (p< 0.001), kind of TKA design (p< 0.001), TKA belonging to the group of revision (0.016) and age at implantation (p< 0.021). A marginal influence was found for the factors: daily activity (p< 0.076) und kind of patella replacement (p< 0.085). Bodymass index and femorotibial axis had no measurable influence on wear.

Discussion: TKA retrieved at autopsy had and astonishingly high amount of wear. As a matter of fact none of the investigated implants was free of delamination, which is the most severe damage mode. In the present sample TKA design and time of implantation had a more important influence on wear than any other factor.