Complicated labral injuries in female patients with developmental dysplasia of the hip are associated with localized stress concentration in the superior acetabulum

Introduction Developmental dysplasia of the hip (DDH) alters joint mechanics and increases the risk of labral injury, compromising hip stability and leading to abnormal stress distribution and cartilage degeneration. However, the relationship between labral injury severity and joint loading stress in DDH remains unclear. This study investigated the effect of labral injury severity on stress distribution in DDH patients using computed tomography osteoabsorptometry (CT-OAM) and finite element analysis. Materials and methods We analyzed 54 hips from 45 female patients undergoing joint-preserving surgery for DDH. Labral injuries were classified as simple or complicated on radial MRI. Subchondral bone density distribution was evaluated with CT-OAM, while finite element analysis of pelvic and femoral bones with cartilage was performed under a single-leg stance to assess contact pressure and area. Statistical analyses examined associations between labral injury severity and stress distribution. Results Superior injuries showed significantly increased high-density area (HDA) in the superior acetabulum, indicating localized stress concentration (simple injury vs. complicated injury, 64.4% vs. 80.3%, p < 0.001). However, finite element analysis revealed no significant differences in contact pressure or area (simple vs. complicated, 5.3 N/mm² vs. 6.2 N/mm², p = 0.538), which we interpret as showing that bony morphology alone could not explain the observed stress patterns. Instead, the discrepancy highlights the role of labral failure reflected in CT-derived subchondral bone density. Conclusion Complicated labral injuries, especially superiorly, were associated with localized stress accumulation in DDH.