A comparison of modeling techniques: using the finite element method to determine local displacements in a human hip

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Artificial hip implant surgery is required by approximately 120,000 Americans each year. A typical hip replacement requires the surgical insertion of an implant into the patient's bone structure. The joint replacement requires permanent fixation an implant to the bone. In most cases, an oversize implant is press-fit into the prepared cavity, which induces stress in the bone around the cavity. Stress is necessary to both hold the implant in place, and to promote bone growth into and around the implant. In an effort to make surgery more successful, three dimensional models of the hip have been developed to help determine optimal placement of implants and to predict complications such as bone fracture upon the insertion of an implant. This thesis presents the steps required to build a three dimensional model of a human hip and provides a comparison of three popular bone modeling techniques used to predict stresses in bone structures. Errors associated with common assumptions for the material properties of bone as well as errors related to simplifications of bone geometry are discussed and validated using finite element models of cantilever beams and human hips. This work concludes with a comparison of three different modeling approaches and how geometry and material properties affect their relative stiffness. The results indicate a model analyzed using solid finite elements throughout predict deflection more realistically than models that attempt to simplify geometry and material properties.