| Summary: | Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. === Page 144 blank. Cataloged from PDF version of thesis. === Includes bibliographical references (pages 141-143). === In the last several years, great strides have been made toward the development of transtibial prostheses that match the functionality of their corresponding biological structures. However, these devices are fundamentally limited because they only emulate the biological ankle-foot complex. In contrast, the gastrocnemius calf muscle spans both the ankle and knee joint, and thus provides biarticular function. Therefore, it may be prudent for transtibial prostheses to include actuation at both the ankle and knee joints of an affected limb. This thesis presents the development of two such biarticular prosthesis systems. The first, tested on two participants, employed a quasi-passive clutched-spring knee orthosis, approximating the largely isometric behavior of the biological gastrocnemius. The second device, tested on six participants, provided positive net mechanical work with a tethered knee orthosis, controlled using a neuromuscular model. Both devices utilized a commercial powered ankle-foot prosthesis. Participants with unilateral transtibial amputation walked with these biarticular prostheses in two separate studies on an instrumented treadmill while motion, force, electromyographic, and metabolic data were collected. Data were analyzed to determine differences resulting from the activation of each knee orthosis, compared to the orthosis behaving as a free-joint. We hypothesized that the active conditions would reduce joint kinetic demands, and consequently metabolic cost, compared to the control conditions. The quasi-passive system was capable of reducing both affected-side knee and hip moment impulse and positive mechanical work in both participants during the late stance knee flexion phase of walking, compared to the control condition. The metabolic cost of walking was also reduced for both participants. The powered artificial gastrocnemius reduced affected-side biological knee flexion moment impulse by 0.022 +/- 0.018 Nm/kg (p = 0.03), and affected-side hip positive work by 0.074 +/- 0.025 J/kg (p = 0.004) during late stance knee flexion, compared to the control condition. However, the data did not support our hypothesis that metabolism would decrease, as two of the participants did not display a metabolic reduction. These results highlight the kinetic benefits of an artificial gastrocnemius for transtibial amputee gait. However, further study is warranted to determine the requirements for achieving a consistent metabolic improvement. === by Michael Frederick Eilenberg. === Ph. D.
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