Musculoskeletal modeling of crouch gait

Crouch gait affects older adults following stroke and is common in children with cerebral palsy. Contracture, spasticity, and increased activation of the hamstrings are often implicated in pediatric crouch gait. Instrumented prosthetics have measured tibiofemoral contact forces in older adults walking in a crouched posture, but contact forces experienced during clinical crouch gait may be much higher. The effect of abnormal muscle forces on knee arthrokinematics and loading of individual knee structures is important to understanding the consequences of crouch gait on developing knees and in older patients with prosthetic components. This project used computational methods that concurrently consider knee anatomy and prosthetic geometry, muscle activation, and body motion to simulate the effect of altered muscle activations on knee loading during crouch gait for a person with an instrumented total knee prosthetic. Measured EMG signals were decomposed into muscle synergies and alterations to synergy weightings provided a means to modify neural command signals in forward dynamics simulations of crouch gait. Open-chain seated leg extension exercises were used to adjust certain muscle properties from generic values and the resulting musculoskeletal model predicted medial and lateral tibiofemoral contact forces within 0.33 and 0.38 bodyweight of measured over one crouch gait cycle. Increasing hamstring activation during stance increased knee loading, posterior tibia translation, and loading on the posterior cruciate ligament.