Effect of personalized liner thickness on the stresses at the stump-prosthesis interface

Abstract

After trans-tibial amputation (TTA) the patient needs prosthesis to maintain mobility, unfortunately, people with this type of amputation often experience skin degradation due to the pressures and shear stresses in the stump-prosthesis interface. The purpose of this study was to reduce the contact pressures and shear stresses at the stump-prosthetic interface In order to design a satisfactory and comfortable prosthesis for the patient. To achieve this we built a trans-tibial finite element model (FE) (stump, socket, and bone, liner) to investigate the stresses at the stump-prosthetic interface. This (FE) model allows comparing the effect of three types of the prosthetic liner (gel liner, Polyurethane foam liner, liner with two layers of foam (foam polyurethane - natural rubber latex foam)) on the contact pressure and shear stress at the stump-prosthetic interface. By modifying the liner thickness (from 3 to 9 mm) in all three cases, one also aim to determine the effect of liner thickness variation on the distribution and intensity of the contact pressure and the shear stress at the stump-prosthetic interface. The comparison of the stresses and their distribution at the stump-prosthesis interface in each case will allow us to determine the optimal prosthesis. The liner with two layers of foam (polyurethane - latex) achieves the best balance between the ability to support the patient’s weight and low stress values at the stump-prosthetic interface, the contact pressure and shear stress values have not been exceeded 42.12 kpa and 15.4 kpa. In general, it can be said that the thickness of the liner was effective in reducing the stresses at the stump-prosthetic interface, in all three cases of liner.