Real-time subject-specific analyses of dynamic internal tissue loads in the residual limb of transtibial amputees

Transtibial amputation (TTA) prosthetic-users may risk the integrity of their residuum while trying to maintain everyday activities. Compression of the muscle flap between the truncated bones and the prosthetic socket may cause pressure ulcers and deep tissue injury (DTI). We hypothesize that mechanical stresses in the muscle flap are higher when walking over complex terrains than during plane gait, and so, the residuum could be at risk for DTI when walking over these terrains. Accordingly, we evaluated internal soft tissue stresses in the residuum at the vicinity of the tibia in 18 prosthetic-users (7 vascular, 11 traumatic). For this purpose, we developed a portable monitor that calculated subject-specific internal stresses in the residuum in real-time. Each subject was studied while walking on plane floor, grass, stairs and slope. We found that internal stresses were the highest while subjects descended a slope, during which internal peak and root mean square (RMS) stresses were approximately 40% and 50% greater than in plane gait, respectively. Peak and RMS stresses calculated while descending a slope were approximately 2 times higher for the sub-group of vascular subjects compared to traumatic, but were similar between the two sub-groups for other ambulation tasks. Overall, the present internal stress monitor is a practical tool for real-time evaluation of internal stresses in the residuum of TTA prosthetic-users in the clinical setting or outdoors. Pending integration of appropriate dynamic tissue injury thresholds, the device can be utilized for alerting to the danger of DTI.