Linear and non-linear finite element modeling of bone-implant system in uncemented total hip arthroplasty
Hou, Fu Joseph
Akin, John Edward.
Doctor of Philosophy
Factors involved in prosthesis performance in uncemented total hip arthroplasty (THA) are complex and many of their effects unclear. Linear and non-linear models were developed to study effects of different factors involved in the bone-implant system. A three-dimensional (3D) unsymmetric beam model, based on a potential energy formulation, for the analysis of stresses in long bones was developed in this research. The cross-sectional properties of the bone were obtained directly from computer tomography (CT) scan data. Variable cross-sectional properties were used along the beam axis. The formulation of the torsional element was based on the torsional theory of thin-walled closed sections and the flexural element bending effects were coupled in two orthogonal directions of unsymmetric bending. Several examples demonstrate that the beam model is efficient and valid in predicting stress profiles in long bones with or without a prosthesis. A systematic method was developed to construct detailed, 3D solid finite element (FE) models from CT scan data. Strains from an intact femur model constructed by this method showed good agreement when compared to published experimental data. The model was also checked by an error estimator for its accuracy. Results from an idealized symmetric 3D model, including non-linear interface elements to model the friction behavior of the bone-implant interface, showed that fully bonded and frictionless assumptions for the interface condition make quite a difference when compared to the friction case. To more accurately model the bone-implant system and to address the problem of implant stability, friction behavior in the interface should be included in the FE model. Through a study of an anatomically realistic bone-implant model under single-leg stance and stair climbing loads, it was shown that stair climbing loads are more threatening than single-leg stance loads to the prosthesis stability, especially the torsional stability. Stair climbing loads should be applied to all uncemented prosthetic devices before their implantations to test their stability in bone. Torsional stability should be rigorously pursued in addition to axial stability for uncemented prosthetic devices.
Biomedical engineering; Mechanical engineering