Radiographic factors affecting contralateral knee alignment in patients with dysplastic hip osteoarthritis.

Introduction: Patients with dysplastic hip arthritis (DHA) often present with abnormal knee alignment. We investigate the factors influencing varus and valgus knee alignment on the contralateral side in patients with unilateral DHA.

Methods: 123 patients with unilateral DHA were enrolled between 2018 and 2022. Based on the hip-knee-ankle angle (HKAA), patients were divided into three groups: neutral group (HKAA <3° varus and valgus), varus group (>3° varus), and valgus group (>3° valgus). Demographics, radiographic parameters, and functional scores were compared between the groups.

Results: There were 58, 44, and 21 patients in the neutral, varus, and valgus group, respectively. The varus group had a varus HKAA and hip adduction angle in the affected hip and a large femoral offset in the healthy hip. The valgus group had a valgus HKAA and large hip adduction angle in the affected hip and a small femoral offset in the healthy hip. In addition, the valgus group presented with pelvic obliquity, expressed as an upper pelvic tilt on the affected side. Multivariate analysis identified a varus HKAA in the affected hip (odds ratio [OR], 0.64; 95% confidence interval [CI]: 0.51-0.79; p < 0.01) as a factor associated with the varus group, while pelvic obliquity (OR, 0.69; 95% CI: 0.53-0.89; p = 0.01) was associated with the valgus group. The varus and valgus groups had significantly worse functional scores than the neutral group.

Conclusions: This study demonstrated that varus and valgus alignments of the contralateral knee with unilateral DHA were associated with radiographic parameters and hip function.