Long-Term Outcomes of Functional Cup Positioned Total Hip Arthroplasty in Asian Ankylosing Spondylitis Patients

Introduction: Total hip arthroplasty (THA) in ankylosing spondylitis (AS) patients are at risk of postoperative complications and dislocation. Functional cup positioning was introduced to address the effect of pelvic malrotation. Our study aims to investigate the long-term survivorship of THA in Asian AS patients. Methods: This is a retrospective study involving Asian AS patients with primary THA between 1970 and 2014. A total of 116 hips in 77 patients were included, with at least 10-year follow-up (mean 20.7 years). Primary outcomes were revision-free and dislocation-free survival of THA up to 30 years. Survival between different fixation methods were compared. Secondary outcomes include postoperative complications, re-revision, and radiographic changes. Results: Mean revision-free survival after primary THA was 23.0 years (95% confidence interval [CI], 21.1 to 24.9), most commonly due to aseptic loosening (54.3%). Overall, 10-year dislocation-free survival was excellent at 99.1% (95% CI, 97.4 to 100.0). Differences between cemented, noncemented, and hybrid THAs were not notable (log-rank test; P = 0.220). Cemented cups (hazard ratio [HR] 17.4; 95% CI, 2.5 to 122.2) and stems (HR 6.9; 95% CI, 1.6 to 30.7) had increased risk of revision due to loosening compared with noncemented THAs. Conclusion: Primary THA in AS patients demonstrated favorable survival at 10 years but poor long-term survival. Functional cup positioning demonstrated excellent results in terms of minimizing dislocation. Cemented implants had greater risk of aseptic loosening in long term, but differences were minimal considering all-cause revision.