Factors associated with symptom development in bilateral hip dysplasia with comparable acetabular coverage

PURPOSE: This study aimed to identify morphological differences between the symptomatic and asymptomatic hips in patients with bilateral hip dysplasia (HD). METHODS: From 109 patients who underwent eccentric rotational acetabular osteotomy (ERAO) between 2017 and 2022, 33 patients were selected as the First Cohort. These patients had undergone ERAO on the symptomatic side, while the contralateral side remained completely asymptomatic for ≥ three years postoperatively. Among them, 18 patients with matching lateral centre-edge angles (CEA) on both sides were selected as the Second Cohort. The acetabular sector angles (ASAs) were measured three-dimensionally. Femoral neck anteversion (FNA) and femoral head lateralization were also assessed. Morphological comparisons between the symptomatic and asymptomatic sides were conducted using paired t-tests in both cohorts. In the Second Cohort, conditional logistic regression analysis was used to identify factors associated with the onset of hip pain. RESULTS: In the First Cohort, the symptomatic side exhibited lower ASAs across the superior-to-anterior acetabulum than the asymptomatic side, whereas no significant differences in ASAs were observed in the Second Cohort. By contrast, both cohorts exhibited greater FNA and lateralization on the symptomatic side. Conditional logistic regression analysis in the Second Cohort identified increased FNA (odds ratio: 1.3) and lateralization (odds ratio: 4.6) as factors associated with hip pain (all p < 0.05). CONCLUSION: When the CEA is comparable on both sides in patients with bilateral HD, morphological features, such as increased FNA and femoral head lateralization, may be more indicative of the symptomatic hip than acetabular parameters.