Mechanical Stimulation in the Residual Femur During Gait in Transfemoral Prosthesis Users Provides a Potential Reason for Bone Mineral Density Loss.

Abstract

Individuals with transfemoral amputation (TFA) experience bone loss in their residual femur at levels seen in bedridden and post-menopausal individuals. It has been suggested that the time until first prosthesis fitting, gait deviations, and muscle atrophy may be contributing factors, but evidence is inconsistent. Prosthetic sockets are typically designed to off-load the distal end of the residual limb, yet the effect of the load transmission pathways of the prosthetic socket on a residual femur has not been examined. Using existing datasets, we recreated the prosthetic socket environment within finite element (FE) models by extracting the skeletal geometries of 10 able-bodied individuals from computer tomography scans, and anthropometrically pairing them with gait data acquired from individuals with unilateral TFA. Normal skeletal geometries were modified to resemble a TFA and fit with an ischial containment socket (ICS). The modified skeleton was positioned with respect to the socket using motion analysis marker locations and tested using the ground reaction forces corresponding to three gait instances from at least four steps. Additional mirror models without the ICS were created for comparison. We validated our study by comparing hip forces from the original gait data to acetabular contact forces estimated using the FE models. We found that the residual femur wearing an ICS experienced mean compressive strain of -105 ± 42 μE and -722 ± 155 μE without the ICS. Simulations show that this is because the ICS redirects load through the pelvis, diminishing force transmission from the femoral head to the acetabulum.