Finite element analysis of stem migration after total hip replacement.

After total hip replacement, the primary and secondary implant stability is critical to ensure long-term success. Excessive migration of the femoral stem can cause implant loosening. In this work, a novel approach for the simulation of the femoral stem migration using the finite element method is presented. Currently, only a few mostly contact-based models exist for this purpose. Instead, a bio-active interface model is used for the bone-stem interface which transforms from the Drucker-Prager to the von Mises plasticity criterion during the osseointegration process. As the position of the implant generally stabilises within one week after the implantation, the migration and osseointegration simulations are decoupled. To understand the effects on the migration, various parameter combinations are examined and a sensitivity analysis is performed. The results indicate that the joint force and the adhesion parameter have the most substantial influence on the migration. Furthermore, the influence of the migration on the subsequent osseointegration process is explored for a numerical example. The proposed model is able to depict the femoral stem migration with values up to 0.27 mm, which are in the order of magnitude of clinically observed values. Further, the model is provided as an open-source Abaqus user material subroutine. Numerical simulation of the stem migration could assist in clinical decision-making by identifying optimal parameter combinations to improve implant stability.