The Distribution Characteristics of Whole-Lower-Limb Axial Torsion: A Large-Scale Developmental Dysplasia of the Hip Cohort Study Reveals Deformities Primarily Located in the Proximal Femur With Rare Tibial Abnormalities

Aims While increased femoral torsion (FT) in patients with developmental dysplasia of the hip (DDH) is well-established, the overall distribution pattern of axial torsion across the entire lower limb remains unclear. This study aimed to define the distribution characteristics of lower limb torsion in DDH by evaluating femoral torsion (including supra-trochanteric and infra-trochanteric regions) and tibial torsion. Methods We conducted a retrospective review of imaging data from patients presenting with hip pain between March 2024 and August 2025. The study included 254 DDH patients (508 hips), with a mean age of 29.6 years, 81% of whom were female. A control group of 61 non-DDH subjects (122 hips) was established. We measured the lateral center-edge angle (LCEA), Tönnis angle, anterior center-edge angle (ACEA), acetabular anteversion angle (AVA), femoral torsion (FT), supra-trochanteric torsion (STT), infra-trochanteric torsion (ITT), and tibial torsion (TT) in all participants. Intergroup comparisons were performed using ANOVA with Bonferroni correction, and regression analysis was used to explore factors influencing FT. Results The DDH group showed significantly greater FT (34.2±10.6 vs. 22.3±19.4, p<0.01), ITT (−12.1±8.0 vs. −16.4±7.8, p<0.01), STT (46.3±9.4 vs. 38.8±7.9, p<0.01), and AVA (22.1±6.6 vs. 16.8±5.1, p<0.01) compared to the control group. Notably, no significant difference was found in TT between the DDH group (22.1±6.6) and the control group (16.8±5.1). Regression analysis indicated that FT was correlated with acetabular deformity parameters such as LCEA. Distribution analysis further revealed that 78% of hips in DDH patients exhibited increased FT, but only 10% showed a concurrent increase in TT. Moreover, three-fifths of the total femoral torsion occurred proximal to the lesser trochanter. Conclusion Through a large-scale cohort assessment of the entire lower limb, this study systematically delineates the axial torsion distribution map in DDH patients: the proximal femur is the primary site of torsional deformity, while abnormal tibial torsion is relatively rare. This finding underscores that clinical evaluation and surgical planning for DDH should focus on deformities of the proximal femur.