"Two Strikes, You're Out": Contemporary Revision Patterns Following Instability after Posterior and Anterior Approach Total Hip Arthroplasty.

INTRODUCTION: Dislocation remains one of the most challenging complications after total hip arthroplasty (THA). Previous studies suggested that three or more dislocations were a threshold for revision; however, these data predate contemporary implants and modern surgical approaches. We used a contemporary cohort of primary THA patients to evaluate the relationship between dislocation recurrence, timing of instability, and subsequent revision for instability.

METHODS: There were 40,315 patients who underwent primary THA at our institution from 2016 to 2024. Among these patients, those who sustained a dislocation event were included. Keyword and diagnosis code search was performed to identify patients, and charts were reviewed to confirm dislocation. A total of 285 patients (0.7%) were included at a mean 5.7-year follow-up, of whom 242 (84.9%) ultimately underwent revision for instability. Instability was categorized by recurrence (one, two, or ≥ three dislocations) and timing (early ≤ 90) versus late (greater than 90 days)). Multivariable logistic regressions were performed to identify factors independently associated with risk of revision.

RESULTS: Revision risk increased sharply with recurrence, rising from 69.1% after one dislocation to 93.9% after two and 98.5% after three or more. Patients who had two dislocations had significantly greater odds of revision than those who had one (odds ratio (OR) 7.70, 95% confidence interval (CI) 3.28 to 20.49, P < 0.001), while risk did not significantly increase beyond the second dislocation. Late dislocations were more likely to result in revision than early events (97.0 versus 74.9%, P < 0.001) and remained independently associated with revision (OR 7.76, 95% CI 2.46 to 35.10, P = 0.002). The association between recurrence, timing, and revision risk was consistent across both approaches.

CONCLUSIONS: In contemporary THA practice, revision frequently occurred after a second dislocation, and late dislocations were more likely to require revision than early events. Future multicenter studies are needed to further refine instability management strategies.