OUTCOMES OF CONVERSION TOTAL HIP ARTHROPLASTY AFTER REVISION OF METAL-ON-METAL RESURFACING: A TEN-YEAR FOLLOW-UP STUDY

Conversion of a failed metal-on-metal (MoM) resurfacing to a total hip arthroplasty (THA) is reportedly a straightforward procedure; however, little has been published regarding implant survivorship, complications and functional results after revision. The primary goal of this study was to assess the outcomes following MoM resurfacing revision. In addition, we tried to assess if the mode of failure had an effect on post-revision outcomes. We reviewed 76 patients that underwent conversion THAs for failed MoM hip resurfacing in our institution. The mean patient age at revision was 58.1 years (range, 32.6–75.4). Causes for revision were adverse local tissue response (ALTR)(25%), loosening of the cup (23.7%), loosening of the head (n=16.4%) femoral neck fracture (13.2%), early femoral head collapse due to avascular necrosis (11.7%), periprosthetic joint infection (PJI) (3.8%) pain without a clear cause (6.2%). All femoral components were revised either to a single-wedged stem (88%) or a cylindrical stem (12%). A hemispherical cup was used in all acetabular revisions (n=65). The cup was not revised in 11 cases (partial revisions). The most recent radiographs were reviewed, while re-revisions and complications were documented. We assessed clinical outcomes using the Harris Hip Score and UCLA Score. Outcomes of conversion THAs according to mode of resurfacing failure were compared. Mean follow up was 10.6 years (range, 3.9–20 years). At final follow up 4 patients were deceased, so 72 patients were available for assessment. The mean HHS score was 86.2 (SD: ±12.9) and the mean UCL was 6.5 (SD: ±2). Seven patients had re-revisions. Five of them had their index revision due to ALTR (2 partial revised resurfacings, 2 developed instability, 1 persisting pain due to pseudotumor) and 2 for infections (1 persisting PJI, 1 acute PJI). The rest of THAs were deemed stable at the most recent radiographs assessment. There were not significant differences in patient reported outcomes in terms of different modes of failure (p>0.05). Survival of conversion THAs was 91.8% at 10 years. Overall, the outcomes after revision for failed MoM hip resurfacings seem to be very good. Conversion THA in this patient group yielded a favorable 10-year survival. Even though patient reported outcomes did not differ between modes of failure, repeat revisions seem to be more frequent in patients with ALTR.