Despite advances in prosthetic foot technology over the last decade, there is growing evidence that individuals with lower-limb amputation (ILLA) are still at a physical disadvantage based on how a prosthetic foot is attached to its leg. ILLA's are missing a physical coupling between their prosthetic ankle and biological knee joint. In non-amputees, this ankle-knee coupling is provided by the gastrocnemius (calf) muscle, which helps a person to transfer power from their ankle to the rest of their body. But this important coupling mechanism is cut during transtibial amputation, which may prevent ILLA's from being able to effectively use power provided by their prosthetic foot. This then forces ILLA's to change their gait in such a way that it may increase their risk of secondary health impairments, like chronic back pain and knee osteoarthritis. The purpose of this research is to test if restoring ankle-knee coupling with an artificial gastrocnemius will improve the way power is transferred from the prosthesis to the body, and thereby improve health and mobility outcomes for ILLA's. First, this study will focus on identifying optimal artificial gastrocnemius properties, for use with both passive (carbon fiber) and powered (motorized) prosthetic feet. Next, the researchers will compare ILLA walking with vs. without the artificial gastrocnemius. During this portion of the study, biomechanical measurements will be used to assess benefits. The proposed artificial gastrocnemius design will be lightweight and comfortably fit underneath clothing, such that it can be easily integrated with existing prosthetic feet to broadly impact the health and mobility of ILLA. These improved outcomes may then help to reduce secondary health comorbidities that contribute to >$8 billion in amputation-related medical expenses in the U.S. each year. The research team brings together interdisciplinary expertise in biomechanics, prosthetic design and clinical care, and students will be involved in all stages of this research. Outreach activities are planned to enhance understanding of the K12 population about working with individuals with disabilities, biomechanics, and prosthetics.
The specific objectives of this proposal are (a) to characterize the effect of gastrocnemius-like ankle-knee coupling dynamics on human walking, then (b) to test the hypothesis that restoring this coupling for individuals with transtibial amputation will improve their gait symmetry and economy while also reducing unhealthy joint loading. Case study data, exoskeleton experiments, and walking simulations provide preliminary evidence that restoring this ankle-knee coupling may be beneficial to ILLA's; however, this has not yet been tested experimentally and it is currently unknown how individual ankle-knee coupling behaviors affect gait, or which are optimal. This study combines various measurement modalities to systematically evaluate biomechanics and mobility outcomes for ILLA walking with a range of ankle-knee coupling behaviors, followed by comparison between walking with vs. without an optimized artificial gastrocnemius. The artificial gastrocnemius will be controlled using a programmable, off-board prosthesis emulator. This study will generate new biomechanical data that provide insight into the functional benefits of ankle-knee coupling in bipedal walking and how these dynamics facilitate power transfer from the ankle. A feasibility study will be performed, with clinical partners, to assess if adding an artificial gastrocnemius will improve health- and mobility-related outcomes for ILLA's while they walk on passive and powered foot prostheses. This approach is innovative because it seeks to improve the function of all prosthetic feet by focusing on the transmission/interface with the body, rather than solely on the prosthetic foot itself. By enhancing walking performance, this research aims to improve mobility and physical activity outcomes for ILLA's.
