The influence of load carriage and foot stiffness on knee joint loading and metabolic cost during amputee walking

Individuals experience sudden load changes during activities of daily living. This added weight places an increased demand on the muscles providing body support, forward propulsion and balance control. For non-amputees, the mechanical output from the ankle muscles are seamlessly modulated to meet the altered demands of load carriage. However, for individuals with a lower-limb amputation, the stiffness properties of standard-of-care prosthetic feet are constant and do not change with varying load conditions. Thus, lower limb amputees often develop gait asymmetries to compensate for the loss of ankle muscles, which may be exacerbated by load carriage. These asymmetries may increase the risk for developing overuse injuries and osteoarthritis in the intact knee as well as elevate the metabolic cost of walking relative to non-amputees. Unfortunately, it is not well understood how prosthetic foot stiffness and load carriage technique influences joint loading asymmetries during amputee gait. The purpose of this study was to use a forward dynamics simulation framework to assess the influence of load carriage technique and prosthetic foot stiffness on knee joint loading and metabolic cost during amputee gait. Forward dynamics simulations were generated to track experimental amputee walking data for each loading condition (unloaded, with a backpack, and with a frontpack) and prosthetic foot condition (four commercially available elastic energy storage and return (ESAR) feet). The results of these simulations showed that amputees rely on their intact limb as a compensatory strategy to meet the increased demands of carrying a load. Carrying the load in a backpack was found to reduce metabolic cost but increase intact knee joint loading. When varying prosthetic foot stiffness, there was no consistent effect on metabolic cost or knee joint loading in any of the three loading conditions. Future work should focus on designing prosthetic components that help reduce the joint loading asymmetry and elevated metabolic cost during load carriage for lower limb amputees. In addition, the tradeoff between metabolic cost and joint loading should be considered when determining the appropriate load carriage technique.Mechanical Engineerin