Evaluations of the hindfoot before and after total knee arthroplasty for patients with varus and valgus knee osteoarthritis

Background Total knee arthroplasty (TKA) corrects coronal knee deformity, but its effects on ankle and hindfoot alignment remain unclear, particularly in valgus knee osteoarthritis (KOA). This study evaluated changes in ankle and hindfoot alignment after TKA in patients with varus and valgus KOA. Methods This retrospective study included 103 varus and 31 valgus knees that underwent primary mechanically aligned TKA. Radiographs were obtained preoperatively and at 6 months. Within-group changes were assessed using paired t -tests. Postoperative values were compared between groups using analysis of covariance adjusted for the corresponding preoperative value; when the homogeneity of regression slopes assumption was violated, change scores were compared using independent-samples t -tests. Results Hip–knee–ankle angle (HKA), mechanical axis percentage (%MA), tibial plafond inclination angle (TPIA), and heel alignment distance (HD) changed significantly in both groups. Knee joint line orientation (KJLO) changed only in the valgus group, and mechanical ankle joint axis point (MAJAP) only in the varus group. Talar tilt (TT) did not change significantly within either group. After baseline adjustment, postoperative MAJAP, TPIA, and HD differed between groups (all p < 0.01), whereas KJLO did not (p = 0.11). Changes in HKA, %MA, and TT also differed between groups (p < 0.01, p < 0.01, and p = 0.046, respectively). Conclusion At 6 months after mechanically aligned TKA, radiographic ankle and hindfoot alignment responses differed between varus and valgus KOA. Because ankle- and hindfoot-specific clinical outcomes and the subtalar joint were not assessed systematically, the clinical significance and mechanisms remain uncertain.