Incidence of the boundary condition between bone and soft tissue in a finite element model of a transfemoral amputee

Background: Many finite element investigations have been made in the field of lower limb prosthetics; however, friction
between bone and soft tissues as a boundary condition has not been considered.
Objectives: To establish whether the change in the contact boundary condition between bone and soft tissues in a transfemoral
amputee affects the stress-strain state on the residual limb.
Study Design: Finite element analysis comparison.
Methods: Finite element models of four transfemoral amputees were developed. In these models the socket, soft tissues
and femur were included and two simulations were made for each model, in one of them the interaction between bone
and soft tissues was defined as tied (there is no relative displacement between surfaces) and in the other it was defined
as a friction boundary condition.
Results: The von Mises stress and strain peaks are higher when the friction definition is used than for tied contact definition.
The distribution pattern of stresses and strains also change when the contact definition varies from tied to friction.
Conclusions: It was concluded that the friction between bone and soft tissues have a significant impact on the results of
finite element models of lower limb prosthetic systems, and therefore in its predictive capabilities.