Transverse-Plane Ankle Rotation for Lower-Limb Amputees Using Two Novel Prostheses

Thesis (Ph.D.)--University of Washington, 2016-06

Lower-limb amputees often suffer from pain and discomfort caused by prosthesis use. Problems include musculoskeletal issues caused by compensatory gait patterns and skin injuries caused by shear stress at the interface between the residual limb and the socket. Torsion adapters have been shown to relieve these skin problems, but are not commonly prescribed due to a perceived decrease in stability. This study describes the Torsionally Active Prosthesis (TAP), a novel prosthesis that aims to provide the same reduction in shear stress as a torsion adapter without the accompanying decrease in stability. The work consists of four parts. First, a powered prosthesis capable of general motion in the transverse plane was developed. Second, exploratory human subject testing was performed to identify a pattern of motion that reduces transverse-plane torque at the socket without reducing torsional stiffness. The results indicate that this can be achieved by coupling transverse-plane ankle rotation with sagittal-plane ankle rotation. Third, the powered prosthesis was configured to perform this axis coupling and human subject testing was performed to determine its efficacy. Three subjects wore the prosthesis and walked at their self-selected speed in straight lines and clockwise and counterclockwise circles with at least three levels of axis coupling, including zero coupling. The subjects showed a trend toward decreased socket torque with increased axis coupling. Finally, the Pivot-Flex Foot (PFF), an unpowered prosthesis that could provide axis coupling was designed, built, and bench-tested. The PFF demonstrated a linear coupling between transverse-plane ankle rotation and sagittal-plane ankle rotation during bench testing.