ABSTRACT of the Doctoral Thesis

Development and Application of 3D CT Image-Based Micro and Macro Finite Element Models for Human Bones and Orthopedic Implant Systems

by Thomas Gross (2014)

Osteoporosis is a bone disease leading to low bone quality and increased risk of fracture. Millions of people around the world are affected and osteoporotic fracture related health care costs have reached an alarming level. In the US alone $19 billion are spent annually on the treatment of osteoporotic bone fractures and, due to an upcoming demographic shift, the predictive annual spendings are expected to double in the next 50 years.

To tackle this problem, tremendous effort is taken to investigate various features of the musculoskeletal system. This thesis focuses on human bone at the microstructural level and the resulting effects on bone strength as well as implant fixation. Simulation models, used by engineers to compute the mechanical competence of bridges, cars and airplanes, can also be employed to study the rigidity and strength of bone structures and orthopedic implants. During the course of this thesis, the finite element (FE) method is used to investigate different aspects of bone biomechanics.

In the first part of this thesis, a framework for large scale nonlinear microFE analyses of trabecular bone structures is established and validated. It is shown that microFE models can predict trabecular bone yielding on the apparent scale purely on the basis of geometric information from micro computed tomography (CT) imaging data. This framework can be used in future studies to investigate the mechanical competence of trabecular bone and orthopedic implants under various loading conditions.

The second part of this thesis focuses on homogenization of trabecular bone structures on different length scales. It is shown that bone remodeling induced mineral heterogeneities at the micro scale do not have an influence on the apparent elastic properties of trabecular bone. Furthermore, microFE based homogenization is performed on a variety of trabecular bone structures from different anatomical locations and morphology-elasticity relationships are established based on either high resolution in-vitro or clinical in-vivo scans.

In the last part of this thesis, a homogenized FE modeling concept for bone analysis is extended for the simulation of volar plate implant systems. In a feasibility study, a CT based FE modeling framework is introduced and two different volar plate osteosynthesis set-ups are compared. Furthermore, the validated nonlinear microFE framework is applied to investigate single screw pull out properties at the micro scale.

revised 140424 (hjb)