Effect of lateral wedge length on knee adduction moment reduction mechanics during gait.

Lateral wedge insole (LWI) wear is a well-known conservative treatment for patients with knee osteoarthritis and is expected to decrease knee joint loading. Although the effect of LWI length on knee adduction moment (KAM) has been investigated, the biomechanical mechanism has not been fully investigated. Twelve healthy young subjects walked in the laboratory with and without 2 different lengths of LWIs. Three-dimensional motion analysis was performed to calculate the first and second peaks and impulses of the KAM during the stance phase. In addition, the knee-ground reaction force lever arm (KLA) and center of pressure (COP), ankle eversion moment, and ankle eversion angle were calculated. The first peak of KAM was lower, COP was displaced outward, and KLA was shorter with both LWIs attached. On the other hand, the second peak of KAM was lower with longer LWIs, COP was displaced outward, and KLA was shorter. The KAM impulse was significantly smaller in the condition with longer LWI than in the other conditions with smaller ankle eversion motion; longer LWI induced COP to the lateral side through the stance phase and kept KLA short, thus reducing the KAM impulse.