EP1.19 Increased Femoral Anteversion in Developmental Dysplasia of the Hip Is Driven Primarily by Proximal Femoral Anteversion: A CT-based Segmental Analysis

Abstract Background Femoral anteversion is frequently increased in developmental dysplasia of the hip (DDH) and is commonly treated as a single composite parameter. However, total femoral anteversion may reflect different anatomic contributions from the proximal femur versus distal femoral torsion, and the segmental source of increased anteversion in DDH remains incompletely defined. Questions/purposes (1) Do hips with DDH demonstrate greater total femoral anteversion than morphologically normal hips, and do contralateral hips in patients with unilateral DDH demonstrate intermediate values? (2) Is any increase in total femoral anteversion in DDH driven predominantly by proximal femoral anteversion (proximal to the lesser trochanter) rather than distal femoral torsion (distal to the lesser trochanter)? (3) Does the proportional contribution of proximal femoral anteversion to total femoral anteversion differ among these groups? Methods We performed a retrospective CT-based study including patients with unilateral DDH and a comparison group without hip dysplasia. In the unilateral DDH cohort, both the dysplastic hip and the contralateral hip were analyzed. Femoral version was quantified as total femoral anteversion (FA), proximal femoral anteversion (PFA; above the lesser trochanter), and distal femoral torsion (DFT; below the lesser trochanter), with FA defined as PFA + DFT. Interobserver and intraobserver reliability were assessed using intraclass correlation coefficients (ICCs). Group differences (control hips, contralateral hips, and dysplastic hips) were evaluated using linear mixed-effects models to account for within-subject correlation, followed by multiplicity-adjusted post hoc comparisons. The proportional contribution of PFA to FA (PFA/FA) was compared among groups. Results Total femoral anteversion differed among groups, with the dysplastic hips demonstrating the greatest anteversion and contralateral hips demonstrating intermediate values compared with controls. The between-group differences in total femoral anteversion were primarily attributable to differences in proximal femoral anteversion, whereas distal femoral torsion did not differ meaningfully among groups. Accordingly, the proportional contribution of proximal femoral anteversion to total femoral anteversion (PFA/FA) was greatest in dysplastic hips and lowest in controls, with contralateral hips again demonstrating intermediate values. Measurement reliability for FA, PFA, and DFT was high (ICCs indicating good-to-excellent agreement). Conclusions Increased femoral anteversion in DDH appears to be driven predominantly by proximal femoral morphology rather than distal femoral torsion, and the contralateral hips in unilateral DDH demonstrate an intermediate segmental version profile. These findings suggest that reporting only total femoral anteversion may obscure clinically relevant anatomic variation. Clinical Relevance Segmental assessment of femoral version (separating proximal femoral anteversion from distal femoral torsion) may improve preoperative characterization of femoral rotational morphology in DDH and provides an anatomic framework for future studies evaluating how version patterns influence surgical decision-making and outcomes.