Functional femoral anteversion in high -riding DDH (Crowe III/IV) differs from normal hips: a CT-based study

The gluteus medius serves as the core functional hub of the hip joint. The greater trochanter’s spatial positioning exerts a pivotal influence on its functional efficacy. However, anatomical anteversion (AA) inadequately describes this spatial position in developmental dysplasia of the hip (DDH). This study applied the previously described functional femoral anteversion (FA) measurement to quantify axial variations across Crowe subtypes, providing guidance for rotational correction of the greater trochanter during THA. This was a single-center retrospective cohort study. The cohort comprised bilateral hips of patients with unilateral DDH (Crowe I, II, III, IV false acetabulum, IV high dislocation) and unaffected contralateral hips of patients with unilateral osteonecrosis of the femoral head (ONFH), which served as the control group. FA, AA, and their discrepancy (FA–AA) were quantified to characterize the axial spatial positioning of the greater trochanter. In this study, the control group had a mean FA of 27.54°, while Crowe I, II, III, IV false acetabulum, and IV high dislocation subtypes showed mean FA values of 31.55°, 35.08°, 43.79°, 41.93°, and 44.61°. The absolute discrepancy between FA and AA was significantly larger in the dysplastic hips of Crowe III/IV DDH patients than in controls. The maximum individual FA-AA discrepancy on the affected side in Crowe III/IV DDH exceeded 10°. On the affected side, FA, AA, and FA-AA all showed significant differences compared to the control group ( P < 0.01), whereas no significant differences in contralateral FA-AA were observed across groups. Our study elucidates axial positional variations of the greater trochanter in hip dysplasia. The dysplastic side in Crowe III/IV DDH demonstrates a distinct structural–functional dissociation between FA and AA, while the contralateral side has mild anatomical changes but maintains normal structural–functional coupling. These findings provide a biomechanical rationale for considering rotational correction during subtrochanteric osteotomy in Crowe III/IV DDH, although its clinical benefit requires prospective validation. Level IV, retrospective study.