Experimental validation of the Lower Leg Trajectory Error, an optimization metric for prosthetic feet

Abstract

In India alone, there are about one million people with lower limb amputation who require significantly more effort to walk than able-bodied individuals. They are subject to social stigmas preventing them from employment and independent living. There is a gap between the high-performance prosthetic feet in the United States that come at a cost of thousands of dollars and affordable prostheses in the developing world, which lack quality, durability and performance. The aim of this project was to design a high-performance, mass-manufacturable passive prosthetic foot for Indian amputees that complies with international standards at an affordable cost. This work was conducted in collaboration with Bhagwan Mahaveer Viklang Sahayata Samiti (BMVSS, the Jaipur Foot organization), in Jaipur, India. Through a novel, quantitative method called Lower Leg Trajectory Error (LLTE) which maps the mechanical design of a prosthetic foot to its biomechanical performance, we can optimize the compliance and geometry of a passive prosthesis to replicate able-bodied gait and loading on the foot using affordable materials. This thesis is focused on evaluating the accuracy and validity of the LLTE as a novel design tool. To validate feet designed using the LLTE, field trials and clinical testing were performed on prosthetic feet prototypes with varying stiffnesses and geometries. The novel merits of these prototypes are that they can replicate a similar quasi-stiffness and range of motion of a physiological ankle using interchangeable custom U-shaped constant stiffness springs ranging from 1.5 to 24 Nm/deg and having up to 30' of range of motion. Initial testing conducted using these feet validated the consitutive model of the LLTE and suggested that prosthetic feet designed with lower LLTE values could offer benefits to the user. In future work, the validated design tool will be used to create high-performance, low-cost and mass-manufacturable prosthetic feet for amputees, throughout the developing world and in the developed world.