Integrated Prosthetic Leg Design Frameworks for People with an Above-Knee Amputation

Abstract

A well-fitting, high-performance prosthesis for people with a lower limb amputation can greatly improve users’ mobility and quality of life. Still, many amputees lack access to high-performance prosthetic components due to the cost and availability of continuous care. This thesis aims to design low-cost, high biomechanical performance above-knee prosthetic leg components (prosthetic foot and knee) that will result in a walking motion likely to be perceived as able-bodied after minimal acclimation time. Above-knee amputees have two common gait deviations from able-bodied and below-knee amputee gait: lack of early stance knee flexion (ESF) and delayed initiation of knee flexion (IOF) during late stance phase. These deviations are likely a result of prioritization of stability at the expense of other functions such as shock absorption and progression through stance. A preliminary perception study was conducted to investigate the acceptable bounds of gait deviation that can be incorporated into a prosthetic leg design without compromising the perception of "typical" walking. Using these results, I created the Hip Trajectory Error (HTE) framework for designing prosthetic feet specifically for people with an above-knee amputation. The HTE framework takes into account the lack of ESF by incorporating the shock absorption function of ESF within the prosthetic foot design. This is achieved by targeting able-bodied hip center motion, which is correlated with sufficient shock absorption during the stance phase. This thesis presents an optimization and performance evaluation process that resulted in a prosthetic foot structure that not only closely replicates able-bodied hip center motion but also could be manufactured for a low cost. An experimental study successfully demonstrated that the Hip Trajectory Error (HTE) framework can be used to predictively design prosthetic feet for aboveknee amputees. HTE-designed prosthetic feet enable comparable biomechanical performance to daily-use tuned and prescribed prosthetic feet within 10-15 minutes of acclimation time and without iterative multi-day fittings. Next, I proposed a method to recommend a damping coefficient for the prosthetic knee to achieve able-bodied peak knee flexion during swing phase. A range of recommended damping coefficients to achieve target peak knee flexion angle in transfemoral amputees was determined using a simple three-step framework. This framework incorporates effects from common transfemoral prosthetic gait deviations, such as slower self-selected walking speeds and delay in initiation of knee flexion during late stance. The calculated range of recommended damping coefficients was experimentally investigated and found to enable a peak knee flexion angle within two standard deviations of able-bodied peak knee flexion angle. Lastly, I created the Full Leg Optimization (FLO) framework to design the prosthetic foot and knee concurrently based on minimal inputs from the user and the prosthetist. The framework anticipates the lack of ESF and delay initiation of late stance knee flexion and uses the HTE framework to predict the orientation and location of the knee mechanism. Using this prediction, the rotational axes of the prosthetic knee can be positioned to start knee flexion at a point in late stance chosen by the prosthetist to provide sufficient stability to the user. A proof-of-concept study demonstrated the accuracy of the prediction for one user after minimal acclimation time, confirming the ability to predictively design prosthetic leg components in tandem. The FLO framework can therefore be used to predictively design a passive prosthetic leg for above-knee amputees while considering common gait deviations due to stability needs. This doctoral work demonstrates that the presented frameworks can be used to quantitatively design prosthetic feet and knees based on the needs of above-knee amputees, which could save fitting time, manufacturing cost, and improve mobility.