The effect of cortical thickness and thread profile dimensions on stress and strain in bone-anchored implants for amputation prostheses

Skeletal attachment of limb prostheses ensures load transfer between the prosthetic leg and the skeleton. For individuals with lower limb amputation, these loads may be of substantial magnitude. To optimize the design of such systems, knowledge about the structural interplay between implant design features, dimensional changes, and material properties of the implant and the surrounding bone is needed. Here, we present the results from a parametric finite element investigation on a generic bone-anchored implant system of screw design, exposed to external loads corresponding to average and high ambulatory loading. Of the investigated parameters, cortical thickness had the largest effect on the stress and strain in the bone-anchored implant and in the cortical bone. 36 % – 44 % reductions in maximum longitudinal stress in the bone-anchored implant was observed as a result of increased cortical thickness from 2 mm to 5 mm. Changes in thread depth had larger effect on the maximum stresses in the fixture and the bone than changes in thread root radius within the evaluated parameter space. Stress reductions in the percutaneous abutment were obtained by autologous transplantation of bone tissue distal to the fixture. Results from this investigation may guide structural design optimization for bone-anchored implant systems for attachment of limb prostheses.