Effects of changes in cadence, prosthetic componentry, and time on interface pressures and shear stresses of three trans-tibial amputees

Objective. To evaluate the effects of changes in cadence, prosthetic compon entry, and time on interface pressures and resultant shear stresses in tran s-tibial amputee case studies. Design. Interface stresses were monitored using custom-designed instrumenta tion at 13 sites on three subjects with unilateral trans-tibial amputation walking with patellar-tendon-bearing prosthetic limbs. Background. Previous studies suggested that week-to-week residual limb chan ges altered interface stresses more than did alterations in prosthetic alig nment. No studies investigating effects of changes in cadence or componentr y on interface stress distributions nor comparing their influence with week -to-week changes have been conducted previously. Methods. Five different prosthetic componentry configurations were tested a t each of three cadences in four sessions. Data were analysed for the magni tudes and timings of peak pressures and resultant shear stresses as well as corresponding resultant shear angles. Results. None of the three cadences or five componentry configurations cons istently induced significantly (P < 0.05) higher or lower interface stress magnitudes for all subjects. However, an Aluminium Pylon/SACH Foot combinat ion compared with an AirStance (pneumatic shank)/Seattle LightFoot unit ind uced later peak interface stress timings as a percentage of stance phase. H igher and more frequent interface stress changes were seen between the week ly sessions than between different cadences or between different componentr y configurations. Conclusion. The amputees' capabilities to compensate for week-to-week resid ual limb changes were less than these for intrasession cadence or component ry alterations. (C) 2000 Elsevier Science Ltd. All rights reserved.