Meta-analysis of uncemented femoral stems shows subsidence and retroversion patterns vary by coating and surgical approach

BACKGROUND AND PURPOSE: We conducted a systematic review and meta-analysis of radiostereometric analysis studies of primary uncemented femoral stems to investigate their subsidence and retroversion patterns and the migration patterns according to implant, patient, and study characteristics. METHODS:  A systematic search of PubMed, Web of Science, Cochrane, and Embase databases to identify all radiostereometric analysis studies on femoral stem migration following primary uncemented total hip replacement was performed. Clinical studies with 2 or more postoperative radiostereometric measurements within 2 years were included. Subsidence and retroversion at 6 weeks, 3 and 6 months, 1, 2, 5, and 10 years were included for analysis. Extracted implant characteristics included implant design, coating, and surgical approach. Data was analyzed using a random effects model. RESULTS:  73 studies on 120 cohorts and 2,970 uncemented stems were included. 119 cohorts reported on subsidence and 91 on retroversion. The pooled subsidence at 3 months was 0.29 mm (95% confidence interval [CI] 0.19-0.39) and 0.32 mm (CI 0.21-0.43) at 2 years. The pooled retroversion at 3 months was 0.51° (CI 0.33-0.70) and 0.70° (CI 0.48-0.93) at 2 years. Hydroxyapatite-coated stems showed the least migration (subsidence 0.26 mm; CI 0.13-0.40; retroversion 0.51°; CI 0.22-0.80) among different coating types. The anterior approach showed more migration (subsidence 1.04 mm, CI 0.53-1.55; retroversion 1.52°, CI 1.08-1.95) than other surgical approaches. CONCLUSION:  Our study shows that most subsidence and retroversion of uncemented femoral stems occurs during the first 3 months. Stabilization of subsidence occurred after 3 months, and retroversion stabilized after 2 years. Migration patterns differ based on stem type, coating, surgical approach, the time period when inclusion started, and timing of baseline measurement.