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Title Determination Of Optimal Counter-Mass Location In Active Prostheses For Transfemoral Amputees To Replicate Normal Swing
Publication Date
University/Publisher Marquette University
Abstract Transfemoral amputees suffer the loss of the knee and ankle joints, as well as partial or complete loss of many of the lower extremity muscle groups involved in ambulation. Recent advances in lower limb prostheses have involved the design of active, powered prosthetic knee and ankle-foot components capable of generating knee and ankle torques similar to that of normal gait. The associated onboard motors, conditioning/processing, and battery units of these active components result in increased mass of the respective prosthesis. While not an issue during stance, this increased mass of the prosthesis affects swing. The goal of this study is to develop and validate mathematical models of the transfemoral residual limb and prosthesis, expand these models to include an active ankle-foot, and investigate counter-mass magnitude(s) and location(s) via model optimization that might improve kinematic symmetry during swing. Single- (thigh only, shank only) and multi-segment (combined thigh and shank) optimization of counter-mass magnitudes and locations indicated that a 2.0 kg counter-mass added 8 cm distal and 10 cm posterior to the distal end of knee unit within the shank segment approximated knee kinematics of able-bodied subjects. This location, however, induced artificial hip torques that reduced hip flexion during swing. While such a counter-mass location and magnitude demonstrated theoretical potential, this location is not clinically realistic; mass can only be added within the prosthesis, distal to the residual limb. Clinically realistic counter-masses must also keep the total prosthetic mass to less than 5 kg; greater mass requires supplemental prosthetic suspension, would likely increase energy expenditure during ambulation, and contribute to increased likelihood of fatigue even with active prosthetic components. The ability to simulate the effects of active prosthetic components inclusive of varying placement of battery and signal conditioning units may advance the design of active prostheses that will minimize kinematic asymmetry and result in greater patient acceptance.
Subjects/Keywords Active ankle, Counter-mass, Powered Prosthesis, Transfemoral Amputee
Contributors Silver-Thorn, Barbara, Voglewede, Philip, Harris, Gerald
Country of Publication us
Format application/pdf
Record ID oai:epublications.marquette.edu:theses_open-1204
Repository marquette
Date Retrieved
Date Indexed 2020-09-17

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…bodied lower limb and a TF residual limb and prosthesis with a Total Knee 2000 and an active ankle-foot (prosthetic components commonly prescribed for active TFAs), 2) evaluation of these computer models using normal gait data from the…

…literature [20] as well as motion data from a physical model of the TF residual limb and prosthesis, and 3) use of these models to identify promising counter-mass magnitude(s) and location(s) to offset heavy, active

…Table 11: Physical models of the TFA pseudo-residual limb and prosthesis ................... 58 Table 12: Optimization trials and corresponding variables used to determine countermass magnitude(s) and location(s) for the thigh and…

…linear approximation of normalized hip torque from four TFAs wearing a prosthesis incorporating a Total Knee 2000 ................................................... 65 Figure 23: Potential counter-mass locations near the knee unit, at the distal thigh…

…prostheses have involved the design of active, powered prosthetic knee and ankle-foot components. These designs are able to generate knee and ankle torques similar to that of normal gait [1-11]. Onboard motors and conditioning/processing units…

…located at the knee and ankle provide prescribed torques (and variable damping) based on various kinematic, kinetic, and/or neural control signals. In addition to the increased mass of the active components, the prosthetic limbs also must…

…incorporate the mass of the battery. While not an issue during stance, the increased mass of the prosthesis affects swing. Prior studies [12-19] have investigated the effects of mass magnitude and location on swing kinematics using passive…

…prosthetic components. Both theoretical models and experimental analyses have shown that adding mass proximally on the shank segment improves kinematic symmetry during swing. For active prosthetic limbs, the addition of counter-weights to offset the mass of…