In vivo quantification of knee-orthosis valgus-corrective moment during gait: Effects of medial strut length on external knee adduction moment in medial knee osteoarthritis

Osteoarthritis (OA) is a progressive degenerative disease affecting articular surfaces, and knee orthoses are commonly employed to reduce the external knee adduction moment (EKAM). However, quantitative data on the corrective moments generated by orthoses during gait and their relationship with EKAM remain limited. This study quantified the corrective moments generated by a knee orthosis using a six-axis force sensor and evaluated the impacts of medial lower-leg strut length on these moments and EKAM, aiming to elucidate the biomechanical mechanisms by which orthotic design facilitates unloading in patients with medial knee OA. Sixteen individuals with medial knee OA participated in gait assessments under three conditions: no orthosis and two orthosis configurations differing only in medial lower-leg strut lengths. The same orthosis model was employed for all participants. Only the medial lower-leg strut length was modified between conditions. Kinematic data and ground reaction forces were collected to calculate EKAM, whereas corrective moments were collected concurrently. Because several variables violated normality, nonparametric statistical analyses were employed as appropriate. The 192-mm orthosis generated greater corrective moments than the 152-mm orthosis throughout all the gait phases. During the loading response phase, EKAM was significantly reduced with the 192-mm orthosis compared with both the 152-mm orthosis and no-orthosis cases (p < 0.01). Furthermore, an inverse relationship was observed between the corrective moment and EKAM, indicating that higher orthosis-generated corrective moments were associated with lower EKAM values. Therefore, the medial strut length may be associated with differences in corrective moments and phase-specific reductions in EKAM. These findings indicate that increasing the medial lower-leg strut length may enhance the corrective moment generated by the knee orthoses, leading to phase-specific reductions in EKAM. This suggests that medial strut length is a clinically relevant design parameter for optimizing biomechanical unloading in patients with medial knee OA.