Finite element analysis of the interface stresses between the stump and socket for a below-knee amputee

Distribution of the interface stresses between the stump and the socket is an important consideration in the prosthetic design and fitting process. By using CT scans, we obtained the coronal plane geometry of the subject's stump with PTB prosthesis but without weight bearing. The stump and socket's boundaries were detected using image processing software to create a frontal two-dimensional mesh model. The lateral liner and socket boundary of the model were shifted with various distances, namely, 2mm, 4mm, 6mm, 8mm, and 10mm in the proximal (P) direction. This shifting was repeated in the distal (D), medial (M) and lateral (L) directions. This approach produced four variable P, D, M, and L groups, and each of these had five different socket sizes in accordance with the five various displacements. This study thus investigated the stress distribution for PTB socket through a plane strain finite element analysis in the frontal section by varying a fitted socket with twenty different sockets' shapes. From the results, it is clear to see that there were little displacement effects for the upward-downward shape change and the tight-loose size changes produced larger displacement effects on frontal socket design. As for the interface stress distribution, all groups produced a higher pressure than the fitted socket (especially on tighter group). But the pressure distribution did not increase with the increasing displacement of shape change for all groups except the tighter group.