Ankle Exoskeleton Assistance Reduces Knee Contact Force during Walking in Individuals with Cerebral Palsy

Musculoskeletal health is critical for physical and mental well-being. Most people with cerebral palsy (CP) experience gait disorders that are associated with increased joint loading, pain, and degeneration. Wearable assistive devices can improve mobility and gait mechanics in those with CP, but their effects on joint loads remain unknown. This study sought to quantify the effects of ankle exoskeleton assistance on knee contact force in people with CP. Eleven children and young adults with CP walked on a treadmill with just shoes (Shod) and with ankle exoskeleton assistance (Exo). Muscle forces were estimated using an electromyography-informed (EMG-informed) modeling approach, where EMG signals from eight lower limb muscles were used to constrain muscle activations. Compressive knee contact force was then quantified based on estimated muscle forces. Ankle assistance reduced peak late-stance knee contact force by 9.3 ± 7.3% and average stance-phase knee contact force by 7.2 ± 4.6% compared to Shod (p ≤ 0.003). Ankle assistance also reduced stance-phase quadriceps muscle force by 9.1 ± 10.9% compared to Shod (p = 0.015). Exo-induced reduction in quadriceps force was associated with lower knee contact force (p < 0.001). Despite the lack of group-level differences in gastrocnemius force or joint kinematics between Shod and Exo, greater knee extension, greater ankle plantarflexion, and lower gastrocnemius force were associated with lower knee contact force (p ≤ 0.022). Our study indicates that ankle assistance may decrease knee loading in people with CP due to changes in knee extensor muscle forces during walking.