An Unnoticed Femoral Condyle Deformity in Transverse Plane Is Associated With Knee Valgus in Patients With Unilateral Developmental Dysplasia of the Hip.

Objective: Patients with developmental dysplasia of the hip (DDH) are usually accompanied by knee valgus, and the previous studies mainly focused on the deformity of the knee in the coronal plane that led to knee valgus. In the transverse plane, the deformity of the femoral condyle had never been considered. This study aimed to analyze the transverse morphology of the femoral condyle in patients with unilateral DDH and explore the correlation between the morphology of the femoral condyle and lower limb alignment.

Methods: Sixty-seven patients (10 male and 57 female) with unilateral DDH in our center between May 2019 and March 2024 were retrospectively analyzed. Then, the lengths of each part of the femoral condyle were collected from CT, and the ratios of anterolateral condyle to anteromedial condyle (ALC/AMC), posterolateral condyle to posteromedial condyle (PLC/PMC), lateral condyle to medial condyle (LC/MC), anterolateral condyle to posterolateral condyle (ALC/PLC) and anteromedial condyle to posteromedial condyle (AMC/PMC) were calculated. Then, the patients were grouped by Crowe classification to further analyze the morphology of the distal femur condyle. The mechanical axis deviation (MAD) of the lower limbs was evaluated. The Pearson correlation coefficient was used to explore the correlation between knee valgus and the morphology of the femur condyle.

Result: Compared with the contralateral side, the ratio of ALC/PLC (p < 0.001) and the ratio of AMC/PMC (p = 0.031) in the ipsilateral side were significantly greater. Grouped by Crowe classification, the greater ratio of ALC/PLC (p < 0.001) in the ipsilateral side could be found in patients with Crowe III and IV DDH. The greater ratio of AMC/PMC (p = 0.003) was only found in patients with Crowe IV DDH. When the four Crowe type sides are compared with each other, the ratio of ALC/PLC in patients with Crowe III and IV DDH is greater than that of patients with Crowe I and II DDH (p = 0.005). The ratio of AMC/PMC in patients with Crowe IV DDH is greater than that of other Crowe type patients(p = 0.003). Besides, as the severity of DDH increases, the MAD increased, which was correlated with the ratio of the ALC/PLC (r = 0.609, p < 0.001) and the ratio of AMC/PMC (r = 0.229, p = 0.031).

Conclusion: Patients with unilateral high-riding DDH could present with an increased ratio of anterolateral condyle and posterolateral condyle on the ipsilateral side, which may be associated with the occurrence of knee valgus. Level III, prognostic study.