Ambulation with a prosthetic limb: Mechanical stresses in amputated limb tissues

The purpose of this research was to measure stresses applied to a below-knee amputee residual limb within a prosthetic socket during ambulation. Both normal stresses and shear stresses were measured during clinical trials using custom-designed transducers. Forces and moments in the prosthetic shank, which provided an assessment of gait, were measured simultaneously.;Results from three amputee subjects showed the following: (1) Peak normal stresses during stance phase ranged from 23kPa to 184kPa. Resultant shear stress maxima ranged from 5kPa to 44kPa. (2) Though interface stress waveform shapes varied, there were consistent characteristics evident in waveforms from different steps, i.e. different loading cycles during ambulation. (3) Resultant shear angles on anterior socket surfaces were directed towards the midline of the tibia. Posterior resultant shear angles were directed downward approximately perpendicular to the ground. (4) Maximal stance phase stresses did not drift significantly over the course of a 30-minute session. (5) Maxima from different transducer sites did not all occur simultaneously. (6) For different socket/shank sagittal plane angular alignment settings, peak stance phase interface stress magnitudes changed minimally. (7) Peak normal stresses during walking average 2.36 times those during standing with equal weight-bearing.;An analytical modelling methodology to calculate interface stresses based on mechanical characteristics of a residual limb and prosthesis was developed with the long-term goal of being a tool for prosthetic design. Using residual limb geometry measurements from Magnetic Resonance Imaging data, tissue material properties from the literature, and force and moment measurements from clinical data, a first-generation model was developed of one of the subject residual limbs under clinical investigation. Comparison of model calculations and clinical interface stress data showed: (1) The model consistently underestimated resultant shear stresses. (2) Resultant shear angles were directed more vertically downward in the model than in clinical data. (3) Unlike clinical data, peak stance phase interface stresses changed for different alignment settings.;Further modelling efforts should account for slip at the residual limb/prosthetic socket interface and nonlinear soft tissue properties.