Modified walking shoes for knee osteoarthritis: Mechanisms for reductions in the knee adduction moment

The objective of this study was to examine mechanisms underpinning the reduction in knee adduction moment (KAM) and changes in frontal plane knee-ground reaction force (GRF) lever arm with a modified shoe that incorporates both a variable-stiffness sole and lateral wedging. Thirty individuals with symptomatic knee osteoarthritis (OA) and 30 overweight asymptomatic individuals underwent gait analyses wearing modified and standard shoes. In both groups, there was a decrease in the lever arm (p<0.001), and a lateral shift in the center of pressure (COP) offset (p ≤ 0.001). There was no change in frontal plane or medial-lateral GRF magnitudes, lateral trunk lean or stance duration in either group. There was no significant change in the frontal plane hip-knee-ankle angle in the OA group but a significant decrease in the overweight group (p=0.003). In both groups, changes in lever arm and frontal plane GRF magnitude predicted change in peak KAM (p<0.01), but only change in lever arm predicted change in KAM impulse (p<0.001). In the OA group, changes in COP offset and medial-lateral GRF magnitude predicted change in lever arm (p<0.05), whereas changes in trunk lean and hip-knee-ankle angle predicted change in lever arm in the overweight group (p=0.01). In conclusion, the change in lever arm contributed the most to explaining change in KAM parameters with modified shoes. The change in the lever arm was driven by changes evident at the foot in the OA participants (COP and medial-lateral GRF), and by more proximal changes (hip-knee-ankle angle and trunk lean) in the overweight group.