Change in the weight-bearing line ratio of the ankle joint and ankle joint line orientation after knee arthroplasty and high tibial osteotomy in patients with genu varum deformity

Several studies reported that excessive correction of severe genu varum deformity with total knee arthroplasty or high tibial osteotomy (HTO) could result in ankle joint pain and osteoarthritis progression. However, few studies have evaluated the change in the weight-bearing-line (WBL) ratio of the ankle joint after knee arthroplasty or HTO in patients with genu varum deformities. This study aimed to investigate the change in the WBL ratio of the ankle joint and ankle joint line orientation after knee arthroplasty or HTO in patients with genu varum deformities. We retrospectively evaluated 40 patients (mean age, 69.9 ± 8.0 years) with genu varum deformities of > 5° and underwent knee arthroplasty or HTO. Three radiologic parameters, including (1) the hip-knee-ankle (HKA) angle, (2) WBL ratio of the ankle joint, and (3) ankle joint line orientation relative to the ground (AJLO-G), were assessed using pre-operative and post-operative orthoradiographs. A paired t test was used to evaluate post-operative changes in the three parameters. Correlations between the change in HKA angle and that in the WBL ratio of the ankle joint and AJLO-G were analyzed. The mean HKA angle significantly decreased post-operatively (10.6° ± 5.3° to 1.1° ± 3.4°; P < 0.001). The WBL ratio of the ankle joint increased from 35.8% ± 15.2% to 53.0% ± 17.4% (P < 0.001), with a lateral shift of the mechanical axis. The AJLO-G decreased with valgization of ankle orientation (7.8° ± 4.8° to 0.4° ± 3.8°; P < 0.001). The change in the HKA angle was significantly correlated with that in the AJLO-G (correlation coefficient = 0.716; P < 0.001) but not with the change in the WBL ratio of the ankle joint. Knee arthroplasty and HTO corrected the genu varum deformity, which influenced the lateral shift of the WBL of the ankle joint and valgization of the ankle joint line orientation.