Compensatory Alignment Characteristics of Coronal Spinopelvic and Lower Leg Alignments in Patients With Crowe Type IV Developmental Dysplasia of the Hip.

Introduction We aimed to investigate compensatory alignment characteristics of coronal spinopelvic and lower limb alignments in patients with unilateral Crowe type IV developmental dysplasia of the hip (DDH). Methodology We conducted a cross-sectional study of 87 patients with unilateral Crowe type IV DDH at our hospital between September 2005 and August 2015. Using standing anteroposterior radiographs of the thoracic and lumbar spine, pelvis, and lower limbs, the inter-ankle height difference, mechanical axis percentage (%MA), leg length discrepancy, pelvic inclination, and Cobb angle were assessed. Spearman's rank correlation coefficient (ρ) was used to evaluate the associations between the inter-ankle height difference and other coronal spinopelvic and lower limb alignment parameters. For the relationships between the inter-ankle height difference and each alignment, multivariable linear regression analysis was performed to calculate adjusted β coefficients, controlling for age, sex, and body mass index. The inter-ankle height difference was treated as the dependent variable, and the other alignments were treated as independent variables. Results The mean age was 65.1 ± 8.6 years, and 77 patients (88.5%) were female. Spearman's rank correlation analysis demonstrated a significant positive weak correlation between the inter-ankle height difference and pelvic inclination (ρ = 0.335, p = 0.002). The inter-ankle height difference showed marginal significant weak association with %MA (ρ = 0.206, p = 0.055) and the Cobb angle (ρ = 0.192, p = 0.075). In contrast, no significant correlation was observed between the inter-ankle height difference and leg length discrepancy (ρ= 0.039, p = 0.721). In multivariate linear regression analysis, the inter-ankle height difference was significantly associated with pelvic inclination (adjusted β = 1.100, 95% CI 0.532-1.669) and Cobb angle (adjusted β = 0.330, 95% CI 0.039-0.620). No significant associations were observed with %MA or leg length discrepancy. Conclusion This cross-sectional study demonstrated that ankle-level compensation was significantly associated with pelvic inclination and showed a borderline association with spinal alignment in patients with unilateral Crowe type IV DDH, whereas knee alignment showed no robust association. These findings suggest that compensatory alignment changes for long-standing leg length discrepancy tend to be observed at the pelvic level, with secondary involvement of the spine rather than the knee.