Clinical measurement of normal and shear stresses on a trans-tibial stump: characteristics of wave-form shapes during walking.

Stresses on the surface of a stump within a prosthetic socket during walking can potentially traumatize stump tissues. To gain insight into stresses and design parameters that affect them, normal and shear interface stresses were measured on three unilateral trans-tibial amputee subjects during walking trials. During stance phase repeated characteristics in wave-form shapes from different subjects were apparent. They included "loading delays", "high frequency events (HFE's)", "first peaks", "valleys", "second peaks", and "push-off". Characteristics did not necessarily occur at the same time from one step to the next but their timings matched well with events in shank force and moment data which were collected simultaneously. For "plantarflexion" and "dorsiflexion" alignment changes, the above wave-form characteristics were still present but their timings within the stance phase changed. The physical meaning and relevance of the characteristics to stump tissue mechanics are discussed.