Abstract
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.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
