Salvaging failed metal-on-metal hip resurfacing with a polyethylene acetabular revision.

Background: Metal-on-metal implants have been used extensively for hip resurfacing arthroplasty (HRA). When failure occurs from reaction to metal wear debris, implant loosening or instability, conversion to total hip replacement (THR) has been the most common treatment. Acetabular failure can also be addressed by revision to a polyethylene acetabular component, providing the patient with a functional resurfaced hip, which many patients want. Acetabular revision with an intact femur is difficult and it is not always possible to find a matching polyethylene acetabular component. The objective of this cohort study is to determine the results of acetabular revision from metal to polyethylene. The further objective is to determine if a polyethylene liner 1 mm larger than the femoral component can also be successful. Methods: From 1999 to 2020, the author performed 326 revisions of metal-on-metal acetabular resurfacing implants to an acetabular polyethylene component. In 164 patients, the polyethylene used was 1 mm larger ("mismatch") than the femoral component because a closer match was not available. In 162 patients, there was a direct size match ("match") of the polyethylene to the retained femoral component. In this original review study, patient demographic data and patient-reported outcomes measures were collected using Harris Hip Score (HHS), Hip Disability and Osteoarthritis Outcome Score (HOOS), and University of California Activity Score (UCLA). Radiographs and component retrievals were studied for wear. Implant survivorship and need for re-revision were the main indicators of success. Results: The mean follow-up period was 13 years (range, 5-26) for 153 patients in the matched group and 157 patients in the mismatched group. Three patients in each group were lost to follow-up, six patients in the matched group and four in the mismatched group died during the follow-up period. There were seven mismatched and six matched retrievals postmortem or during revision available for wear studies. The mean outcome scores were HOOS 91, HHS 92, and UCLA 7. There were no differences in the results of the outcome measures, complications, implant survivorship, or wear noted on the retrievals between the matched and mismatched groups. There were 9 (5.9%) re-revisions in the matched group and 8 (5.1%) in the mismatched group. Conclusions: Patients treated by exchanging their failed metal-on-metal HRA acetabular component with a polyethylene component had good outcomes and low re-revision rates. The acetabular wear seen on retrievals was low and consistent with a lifetime of use in most but not all cases. The conclusion is that acetabular revision to polyethylene for resurfacing is safe and effective when the size is matched or mismatched by 1 mm. A single surgeon performed all the procedures and others might not achieve these results. Caution is necessary before extending these findings to other procedures such as revision THR.