Design and Evaluation of a Novel Ankle Joint for an Ankle Foot Orthosis for Individuals with Drop-Foot
Date of Award
Master of Science (MS)
Voglewede, Philip A.
Individuals who have had a stroke often ambulate with an ankle foot orthosis (AFO) to treat drop-foot, a common impairment preventing active ankle dorsiflexion. AFOs limit ankle plantarflexion or drop-foot, but also restrict ankle motion that introduces additional gait pathologies during ambulation. The goal of this study was to design a mechanical ankle joint for an articulated thermoplastic AFO to permit enhanced motion during stance. This novel ankle joint operated in two stages: 1) locked during swing to prevent drop-foot and 2) unlocked during stance to allow motion. This novel ankle joint was first tested with able-bodied subjects to ensure device function and safety, subsequent testing was conducted with post-stroke subjects to determine whether the novel design contributed to functional improvements during walking. Three able-bodied (23-26 years) and three post-stroke individuals (52-67 years) were recruited to complete custom AFO casting, fitting, and testing sessions with conventional and novel orthotic ankle joints. Testing included overground and variable slope treadmill walking trials. These gait analyses incorporated motion capture and kinetic data to calculate spatiotemporal, kinematic, and joint moment data. A survey was administered after testing to determine subject perception of the novel ankle joint in terms of comfort, walking performance, and perceived exertion. Paired t-tests were conducted to identify significant differences between orthotic ankle joint conditions.Significant differences between ankle joint conditions were observed for stance duration, step length, and ankle plantarflexion during swing. Stance duration and step length increased for the paretic limb, and corresponding improved inter-limb symmetry for level and non-level terrain. Ankle plantarflexion during swing with the novel ankle joint was controlled, providing adequate foot clearance and increased ankle range of motion during early stance. These improvements in ankle mobility, however, did not contribute to consistent improvements in hip kinematics, nor significant differences in knee and hip kinetics.Design refinement is recommended to support joint tuning and accommodate greater variation in spring stiffnesses. This novel orthotic ankle joint demonstrates promise and clinical potential to treat post-stroke individuals with drop-foot.