Abstract
OBJECTIVE: Developmental dysplasia of the hip (DDH) exhibits abnormalities in hip anatomy, so changes in the acetabular and femoral angles hold clinical relevance. This study aimed to investigate the correlations between acetabular anteversion (AAV) and acetabular abduction (AAB), as well as between combined anteversion and combined abduction in patients with DDH, attempting to give evidence for synchronous torsion of the proximal femur and acetabulum. This study also aimed to propose a new method for predicting acetabular anteversion and combined anteversion angles, respectively, based on acetabular abduction and combined abduction angles on conventional pelvic radiographs. METHODS: This retrospective study included 202 patients (404 hips) with DDH who underwent THA at our institution from February 2013 to September 2021. Preoperative AAB/femoral neck-shaft angle (FNA) was recorded via radiograph. AAV/femoral anteversion (FA) was recorded via computed tomography and radiography. To assess the correlations between the AAV and AAB and between combined anteversion (sum of AAV and FA) and combined abduction (sum of AAB and FNA), linear regressions and Pearson's coefficients were calculated. RESULTS: All hips were categorized into five DDH subgroups according to the Crowe classification: 93 normal, 140 Crowe type I, 68 Crowe type II, 59 Crowe type III, and 44 Crowe type IV. Fairly positive correlations were observed between combined anteversion and combined abduction in normal (r = 0.509), type I (r = 0.637), type II (r = 0.423), and type III (r = 0.511) subgroups. AAV and AAB demonstrated a moderate positive correlation in the normal (r = 0.508), type I (r = 0.511), type II (r = 0.516), type III (r = 0.332), and type IV (r = 0.603) subgroups. CONCLUSIONS: The AAV and AAB, as well as combined anteversion and combined abduction, exhibited positive correlations in normal and Crowe type I-III hips, suggesting the torsion of the acetabulum and synchronous torsion of the acetabulum and proximal femur. These findings quantify synchronized twisting of the hip and offer the potential significant implications for the accuracy of preoperative planning in THA, especially in DDH patients.