Does transposition osteotomy of the acetabulum alter the natural history of developmental dysplasia of the hip?

Aims: The aim of this study was to clarify the natural history of developmental dysplasia of the hip (DDH), borderline DDH (BDDH), and normal hips, and to determine whether transposition osteotomy of the acetabulum (TOA) alters the long-term joint survival in DDH and BDDH. Methods: We retrospectively reviewed 683 hips treated with TOA and 353 contralateral native hips. Hips were classified by the lateral centre-edge angle (LCEA) as DDH (< 20°), BDDH (20° to < 25°), or normal (≥ 25°). The median follow-up was 11 years (IQR 5.8 to 16) for contralateral native hips and 9.6 years (IQR 5.3 to 15) for TOA-treated hips. The cumulative probability of failure (progression to Tönnis grade 3, or conversion to total hip arthroplasty) was estimated using the Kaplan-Meier method. Cox proportional hazards models with patient-level cluster-robust standard errors identified predictors for failure. Results: In native hips, the 20-year survival was significantly lower in DDH than in BDDH and normal hips (69% (95% CI 55 to 80) vs 96% (95% CI 83 to 99) vs 100%, respectively; p < 0.010), with no significant difference between BDDH and normal hips. Increased BMI and decreased LCEA were independent predictors for failure. In DDH, TOA-treated hips had significantly increased 20-year survival compared with native hips (88% (95% CI 80 to 93) vs 69% (95% CI 55 to 80); p < 0.001), and native hip status, older age, and increased BMI were independent predictors of failure. In BDDH, failure-free survival at 20 years did not differ significantly between native hips and TOA-treated hips (96% (95% CI 83 to 99) vs 100%; p = 0.394); however, TOA-treated hips had significantly less progression of osteoarthritis (OA) than native hips (20-year survival: 79% (95% CI 22 to 96) vs 52% (95% CI 30 to 71); p = 0.039). Older age and decreased LCEA were independent predictors of progression of OA. Conclusion: In DDH, the increased long-term survival after TOA supports a potential disease-modifying effect of acetabular reorientation. BDDH showed a low long-term risk of failure and TOA was not significantly associated with improved failure-free survival in this sub-group. These findings indicate that the severity of dysplasia determines distinct long-term outcomes and support the careful selection of patients for TOA in those with BDDH, with the need for further longitudinal evaluation.