Characterization of lower-extremity biomechanics when walking with a hands-free crutch: an integrated experimental and computational analysis

Abstract

Background Lower-leg wounds and fractures are some of the most common types of traumatic injuries sustained by U.S. Service members during combat operations. Existing guidelines for on-field management of lower-leg injuries recommend stabilizing the injury and preventing weight-bearing on the affected leg. However, adhering to these recommendations could be challenging because the casualty may need to walk independently to obtain medical care. In this exploratory experimental and computational study, we assessed the biomechanical characteristics of a hands-free crutch device to aid in the mobility of healthy individuals with a hypothetical lower-leg injury. Methods We conducted an experimental study where we collected anthropometric, body-motion, ground reaction force, spatiotemporal, and electromyography data from 10 young, healthy men who walked with and without the Freedom Leg hands-free crutch on an instrumented treadmill. Using these data, we developed individualized musculoskeletal and finite-element models and computed biomechanical parameters, including joint kinematics and kinetics, muscle activity and metabolic power demand, and tibial stress, for each participant under each of the two walking conditions. We evaluated the suitability of the device by comparing the model-predicted biomechanical parameters between the two conditions. Results Compared to walking unassisted, walking with the Freedom Leg reduced the peak knee joint reaction force (JRF) by 47%, peak ankle JRF by 98%, and peak tibial stress by 59% in the crutch-supported leg. However, it also introduced unintended consequences in the contralateral leg, increasing the peak hip JRF by 19%, peak hip flexion moment by 50%, and peak hip extension moment by 89% as well as the mean metabolic power demand in representative hip and knee muscles. Conclusion The Freedom Leg improved mobility by effectively reducing weight-bearing and stabilizing the crutch-supported leg. However, changes in gait patterns also introduced unintended biomechanical consequences in the contralateral leg. This exploratory study provides insights into the biomechanical effects of walking with the Freedom Leg in healthy, young individuals and may inform the development and assessment of future hands-free crutch devices to improve mobility of Service members with lower-leg injuries.