Abstract
Introduction: Reintroduced in 1988, 28-mm metal-on-metal Metasul bearings had head sleeves and liner rim edge. It was modified in 1995 for the 2nd current design without sleeve and rim. Aim of this study was to address the fate if any of this modification.
Material and methods: 100 consecutive Alloclassic cementless titanium 1ary THA with 28mm-Metasul bearings (22 with head sleeve of the 1st design) were prospectively studied (primary arthritis in 76% of hips, mean age 59.6 years). 2 Metasul components of 1st design were exchanged for dislocation. The remaining 98 THAs were reviewed after a 6-year average follow-up (range, 17–126 months).
Results: Clinical results were graded excellent and good except for 3 patients Radiographically, wear was undetectable in the 97 bearings available for study. Post-operative cobalt level in whole blood was noted superior to the upper “normal” value (5 μg/L) for 16 THAs (3 of the 1st design, 13%). No significant relationship could be established between elevated blood Co level and any demographic or surgical data, including age (p = .61) and activity level (p = .44), except with radiographic aspect of a high anteversion of the cup, noted > 25° in 5 hips: incidentally 4 were of the 1st Metasul design (p = .0037). High dislocation rate (5%) could partly be explained by early impingement favoured by head sleeve and liner rim-edge. In 1 hip, despite excellent clinical result, posterior impingement with an extra-long sleeved head induced elevated Co level that leads to the bearing exchange. In another hip with Metasul head sleeve, the same mechanism induced femoral component aseptic loosening and osteolysis that was revised at 7.8 years. These 2 hips showed the higher Co levels of the series, up to 23.6 μg/L and 36 μg/L, respectively. The difference between revision rates of Metasul bearings of 1st (4/22, 17%) and current design (1/78, 1.3%) was significant (p =.008). At 8 year, survivorship of Metasul bearings from revision for any reason was 81.4% (95% CI, 57–93.5%) for the 1st design and 98.7% (81–99.9%) for the current design. No general toxic effect could have been detected thus far.
Conclusion: In this personal experience, impingement due to metallic head sleeve has been the main cause of osteolysis, and Co level survey has shown to be a good indicator of Metal-on-Metal bearing behaviour. Obviously, Metasul head sleeve should have been avoided.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
