Prosthetic leg socket design: New insight on different tibia length and distal bevelled angle using finite element analysis.

Abstract

Socket is one of the components that can determine the comfort of the user. Poor socket fit can induce pain and discomfort to the residual leg. Besides, poor selection of amputation morphological parameters such as length of bone and tibial bevelling angle can hinder the control of prosthesis. Thus, the surgeon needs to make a wise decision, or else it can cause problems later in prescribing prostheses for the amputee. The aim of the study is to investigate the effect of morphological variability of residual limbs such as tibial length, distal tibia bevelling angle, and stiffness of soft tissue. The residual leg of the volunteer was scanned using a 3D scanner, and a socket was designed based on the contour of the residual leg. The bone 3D model was derived from CT-scanned data and modelled as amputated bone, with the length of the tibia cut to 12.5 cm, 15 cm, and 17.5 cm and the distal is bevelled to 30°, 45°, and 60°. Stiffness of the soft tissue is defined as the D and C hyper-elastic values. From the result, tibial length of 12.5 cm, distal tibial bevelling angle of 45°, and stiffness of 55 kPa are found as the optimal parameters for the volunteer by selecting the lowest maximum von Mises stress of soft tissue for each category. No pain is predicted on the soft tissue during standing since the normal stress is not exceeding the pain threshold at fibular head region (0.89 MPa). The result indicates that the morphology of the residual limb affected the stress distribution on the soft tissue, where for this study specific patient, 15 cm tibial length, 45° tibial beveling angle, and contracted soft tissue are the optimum parameters.