State-of-the-art transtibial prostheses provide only ankle joint actuation and thus do not provide the biarticular function of\nthe amputated gastrocnemius muscle. We develop a prosthesis that actuates both knee and ankle joints and then evaluate the\nincremental effects of this prosthesis as compared to ankle actuation alone. The prosthesis employs a quasi-passive clutched-spring\nknee orthosis, approximating the largely isometric behavior of the biological gastrocnemius, and utilizes a commercial powered\nankle-foot prosthesis for ankle joint functionality. Two participants with unilateral transtibial amputation walk with this prosthesis\non an instrumented treadmill, while motion, force, and metabolic data are collected. Data are analyzed to determine differences\nbetween the biarticular condition with the activation of the knee orthosis and the monoarticular condition with the orthosis\nbehaving as a free-joint. As hypothesized, the biarticular system is shown to reduce both affected-side knee and hip moment\nimpulse and positive mechanical work in both participants during the late stance knee flexion phase of walking, compared to\nthe monoarticular condition. The metabolic cost of walking is also reduced for both participants. These very preliminary results\nsuggest that biarticular functionality may provide benefits beyond even those of the most advanced monoarticular prostheses
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