Retraining Gastrocnemius Muscle Coordination Reduces Late-Stance Knee Contact Force in Individuals With Knee Osteoarthritis.

Musculoskeletal simulations and experiments in young adults without knee pain have demonstrated that reducing gastrocnemius muscle activity can reduce knee contact force, which may reduce pain and progression of knee osteoarthritis. This study investigated whether individuals with knee osteoarthritis could reduce gastrocnemius electromyography (EMG) when provided with haptic biofeedback and consequently reduce late-stance knee contact force. Individuals with tibiofemoral osteoarthritis walked on a treadmill with adaptive biofeedback instructing them to reduce gastrocnemius EMG. Thirteen of eighteen participants reduced their average gastrocnemius EMG by at least 10% during an initial 30-minute training session and thereby qualified for a second session. During the second session, participants received the same biofeedback, and we estimated knee contact force using musculoskeletal models and static optimization. With feedback, participants reduced gastrocnemius EMG by $25\pm 15$ % (p<0.001) and reduced the late-stance peak of knee contact force by 12%, or $0.38\pm 0.47$ times body weight (p= 0.01). However, the average EMG of the vasti muscles increased by $38\pm 34$ % (p= 0.004), which contributed to an increase in early-stance knee contact force in some participants. Ten out of thirteen reduced their knee contact force impulse with the feedback. While additional work is needed to mitigate increases in vasti EMG, our data demonstrates that individuals with knee osteoarthritis can reduce gastrocnemius EMG and late-stance knee contact force in a brief period of training, suggesting the potential of muscle coordination retraining as a non-surgical intervention for knee osteoarthritis.