In vivo quantification of knee-orthosis valgus corrective moment during gait: Effect of medial strut length on EKAM in medial knee osteoarthritis

Osteoarthritis (OA) is a progressive degenerative articular disease, and knee orthoses are widely used to reduce the external knee adduction moment (EKAM). However, quantitative evidence regarding the corrective moments exerted by orthoses during gait and their relationship with EKAM is scarce. This study directly measured the corrective moments generated by a knee orthosis using a six-axis force sensor and assessed the influence of orthosis structure on these moments and EKAM. Sixteen individuals with medial knee OA (Kellgren-Lawrence grade II or III) affecting the left knee performed walking assessments across three test states: without an orthosis, with an orthosis incorporating a 152-mm medial lower-leg strut, and with an orthosis incorporating a 192-mm strut. Kinematic data and ground reaction forces were used to calculate EKAM, while corrective moments were collected concurrently. The 192-mm orthosis generated greater corrective moments than the 152-mm orthosis throughout all gait phases. EKAM during the loading response declined markedly, being lowest with the 192-mm orthosis, intermediate with the 152-mm orthosis, and highest without an orthosis. An inverse association was observed between corrective moments and EKAM, indicating that higher corrective moments corresponded to lower EKAM. Although walking speed slightly decreased with greater corrective moments, stride length was unchanged. These results demonstrate that the length of the medial lower-leg strut determines the magnitude of corrective moments and is pivotal for lowering EKAM. Collectively, the results highlight the importance of optimizing orthosis design to meet the specific biomechanical requirements of patients with medial knee OA.