Prosthesis design based on an asymmetric passive dynamic walker

This paper presents a theoretical design of a transfemoral prosthesis based on physical asymmetries. Breaking the mold of current prostheses, we propose a general prosthetic leg design in which the knee location is shifted off its traditional knee line. The objective is to find an above-knee prosthetic design for which the overall mass is decreased, especially the below knee portion, while still exhibiting a symmetric gait pattern. A lighter prosthetic that enables a symmetric gait will increase the comfort and decrease the detrimental effects of an asymmetric gait for individuals that wear prostheses. In individuals with prosthetics, changing the knee location could also result in a symmetric gait. To analyze the prosthesis, the existing passive dynamic walker model with five masses was adapted to include nine masses to better represent the mass distribution throughout each limb. A search through the parameter space revealed that a symmetric gait could arise from a system with different knee locations on both sides while the mass of the prosthesis was lighter than the existing leg. In order to accomplish this, the knee location of the prosthesis was positioned below the intact knee by 36.7% of the total shank length. This physical asymmetry resulted in a below knee mass reduction of 68.2% and a total mass reduction of 13.4% while having a symmetric gait. In addition, the model gives further indications on where to add or remove mass to decrease the amount of asymmetry in individuals with prostheses and other causes of asymmetric gait.