Evaluating shear and normal force with the use of an instrumented transtibial socket: A case study

An instrumented prosthetic socket evaluated shear and normal forces during walking. The influence of a three ply sock worn within the prosthetic socket was evaluated. Shear and normal forces were highest with the addition of a three ply sock. Increased forces cause a decrease in blood perfusion which may lead to ulcers. Patients with transtibial amputation experience ulcers on their residual limb. The loading between the device and underlying material plays a role in loads transmitted to the skin. The objective was to evaluate normal and shear forces at the socket/liner interface during walking. A 53 year old male (85.45 kg and 177.8 cm) with a transtibial amputation participated in this case study. A transtibial prosthesis was instrumented with a load cell to measure normal and shear forces at the socket interface. Three conditions were evaluated during walking: gel liner, additional three ply sock and a hole in the gel liner. Shear and normal forces were highest with the addition of a three ply. Longitudinal shear stresses ranged from 0.4–7.66 kPa, transverse shear stresses ranged from 0.01–7.79 kPa and normal stresses ranged from 2.7–61.9 kPa. Increased shear and normal forces can cause a significant decrease in blood perfusion, linked to an increased risk of ulcer formation. Experimental force results are also important for future work involving finite element modeling of the skin/liner/device interface.