Varus knee osteoarthritis with ankle osteoarthritis demonstrates greater hindfoot inversion and larger ankle inversion loading during gait following total knee arthroplasty compared to varus knee osteoarthritis alone

Purpose Although patients with varus knee osteoarthritis (KOA) and concurrent ankle osteoarthritis (AOA) may experience increased ankle joint pain after total knee arthroplasty (TKA), the underlying mechanism remains unclear. This study aimed to investigate the effects of concurrent AOA on ankle and hindfoot alignment, frontal plane ankle and hindfoot biomechanics during gait following TKA and the clinical outcomes. Methods Twenty‐four patients with varus KOA who underwent TKA were included in this retrospective cohort study. Patients were categorized into two groups: with and without AOA. Radiographic evaluations of lower‐limb, ankle and hindfoot alignment, and knee and ankle clinical outcomes were conducted preoperatively and 6 months postoperatively. In addition, gait analyses were performed to investigate knee, ankle and hindfoot kinematics and kinetics. Each data was compared between patients with and without AOA. Results Concomitant AOA was found in eight ankles. The AOA group exhibited greater postoperative hindfoot varus and increased postoperative ankle pain than the non‐AOA group. Gait analysis showed no significant differences in knee varus alignment or tibial tilt after TKA between the groups. However, the AOA group demonstrated significantly greater hindfoot inversion and larger ankle inversion loading. Conclusion One third of patients who underwent TKA had concurrent AOA associated with hindfoot varus. Despite achieving proper coronal knee alignment postoperatively, these patients experienced greater hindfoot and ankle joint inversion load during gait. Surgeons should consider the inability to evert the hindfoot and the possibility of increased ankle joint pain when planning and performing TKA. Level of Evidence Level III.