Patient selection refines total hip arthroplasty free survival after hip arthroscopy: an eighteen year, one thousand and fifty one hip cohort study.

PURPOSE: To determine whether improvement in THA-free survival across an 18-year hip arthroscopy series is attributable to progressive exclusion of high-risk patient profiles or to era-specific technical advances, and to identify the radiological selection thresholds most strongly associated with this improvement.

METHODS

Retrospective analysis of a prospectively maintained single-surgeon database. A consecutive series of 1,051 hips operated on for FAI (2007-2025; Tönnis grades 0 to 2) was stratified into four surgical eras. The primary outcome was THA conversion. THA-free survival was estimated by the Kaplan-Meier method; predictors of conversion were identified by multivariable Cox proportional hazards regression.

RESULTS

Eighty-three hips (7.9%) underwent THA conversion over a median follow-up of 53.6 months (5,939 patient-years). Five-year THA-free survival was 91.4% (95% CI 89.3-93.1%) overall and differed significantly across eras (log-rank p < 0.0001). Era II (2012-2015) had the lowest five-year survival (83.3%; 95% CI: 75.5-86.1%), corresponding to the peak prevalence of Tönnis grade ≥ 2 (29.5%) in the entire series. Progressive changes in radiological selection criteria were accompanied by a reduction in severe ALAD lesions identified intraoperatively. The prevalence of Tönnis grade ≥ 2 declined from 29.5% to 10.0% across eras. On multivariable analysis, ALAD grade (HR 2.59; 95% CI 1.58-4.27; p < 0.001), Tönnis grade (HR 2.13; 1.24-3.66; p = 0.006) and age (HR 1.06/year; p < 0.001) were independent predictors of THA conversion; era hazard ratios were non-significant after adjustment for these variables (p > 0.19). The five-year estimate for Era IV (95.9%) should be interpreted with caution given the limited follow-up in this cohort (median 30.8 months). Apparent C-index: 0.911 (95% CI 0.882-0.940); no internal validation was performed.

CONCLUSION

Improvement in THA-free survival over 18 years was closely associated with the progressive reduction in the proportion of operated patients with Tönnis grade ≥ 2. Although technical evolution occurred concurrently, era effects were substantially attenuated after adjustment for patient selection variables. Tönnis grade functions as the primary pre-operative selection variable; ALAD grade, identified intraoperatively, had the highest adjusted hazard ratio for THA conversion and reflects the consequences of pre-operative selection. These findings support the importance of pre-operative radiological selection-particularly Tönnis grade-when interpreting THA conversion rates across institutions and historical surgical series.