Clinical Outcomes and Survivorship After Conversion of Metal-on-Metal Hip Resurfacing to Total Hip Arthroplasty: A Systematic Review.

BACKGROUND Hip resurfacing arthroplasty was developed for younger active patients to preserve bone stock and facilitate future revision; however, failure requiring conversion to total hip arthroplasty (THA) remains a recognized problem. Outcomes after conversion are variable and influenced by indication and technical factors. This systematic review evaluates survivorship, complications, and functional outcomes after conversion of hip resurfacing to THA.

METHODS A systematic review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and registered with International Prospective Register of Systematic Reviews. MEDLINE, Embase, Web of Science, and Cumulative Index to Nursing and Allied Health Literature were searched for studies reporting outcomes after revision of hip resurfacing to THA. Eighteen studies met inclusion criteria. Data were extracted on demographics, indications, revision strategy, complications, survivorship, and functional outcomes.

RESULTS Nineteen studies comprising 1,698 patients and 1,719 hips were included. The mean age was 56.0 years, with mean time to conversion of 4.74 years and follow-up of 3.80 years. The most common indications were aseptic loosening (31.4%), adverse reaction to metal debris (ARMD) (27.1%), and femoral neck fracture (23.7%). Femoral only revision was performed in 36% and both components in 64%. The pooled complication rate was 10.5%, most commonly dislocation, infection, loosening, and ARMD. Survivorship ranged from 94.7% to 100% short term, 83.3% to 94.8% midterm, and 69% to 92% at 10 years, with up to 85.3% at 13 years, and was lower in ARMD. Functional outcomes improved, with mean Harris Hip Score increasing from 47.0 to 88.4.

CONCLUSION Conversion of failed hip resurfacing to THA provides consistent and clinically meaningful improvement in pain and function. However, complication rates remain substantial and long-term survivorship is variable and influenced by the indication for failure. Metal-related pathology and aseptic loosening were associated with less favorable outcomes than mechanically driven failures.

LEVEL OF EVIDENCE Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.