Analysis of the swing phase dynamics and muscular effort of the above-knee amputee for varying prosthetic shank loads

The purpose of this study was to determine the effect of varying prosthetic shank mass, while maintaining the mass centre location and moment of inertia, on the swing phase kinematics, kinetics and hip muscular effort of free speed above-knee (AK) amputee gait. Six AK amputees, wearing similar prosthetic designs, had three load conditions applied to their prosthetic shank: 1) Load 0-unloaded (X = 39.1% sound shank mass), 2) Load 1-75%, and 3) Load 2-100% sound leg mass. Despite increases in shank mass from 1.33 to 3.37 kg the AK amputee was able to maintain a consistent swing time and walking speed. As load increased, there were significant changes in the maximum knee and hip displacements, as well as phasic shifting. The prosthetic knee Resultant Joint Moment (RJM) was negligible while the shank was accelerating (periods 1 and 2), but was a major contributor during shank deceleration (periods 3 and 4). During periods 1 and 2 the principle contributors to the shank acceleration (forces resisting excessive knee flexion) were the gravitational moment (S-G) and the moment due to thigh angular acceleration (S-AT). During the periods of shank acceleration (sections 1 and 2), there was not a significant increase in the hip muscular effort. However, during sections 3 and 4, the periods associated with shank deceleration, there were significant increases in the hip muscular effort. The hip muscular effort for the complete swing phase increased as load increased by 36.7% and 71.3% for loads 1 and 2. Despite the significant increases in hip muscular effort, four of the six subjects preferred load 1 condition.