Knowledge the mechanical behavior and failure mechanisms of trabecular bone is fundamental to understanding the etiology of bone fracture as well as the mechanisms by which aging, disease, and treatment can alter the mechanical competence of bone. The focus of this thesis was to use micromechanical modeling techniques to enhance the current understanding of trabecular bone mechanical properties and failure mechanisms, and to address issues that are relevant to improving clinical predictions of bone strength.

Using state-of-the-art developments in micro-FE analysis, we established that geometrically nonlinear deformations represent an important failure mechanism for low- density bone (BWTVO.20), but are negligible for higher-density bone. Furthermore, incorporation of geometric nonlinearities allowed us to validate the FE models for a wide range of densities and loading conditions. These validated modeling techniques were used to assess the capacity of nonlinear versus linear micro-FE models to predict bone strength at clinical-type resolutions. Results indicated that linear FE analyses had to be conducted with a mesh four times finer than that for nonlinear analyses to achieve equivalent strength predictions, which suggests that incorporation of the nonlinear modeling techniques described in this thesis may be able to improve predictions of bone strength and fracture risk when applied to the in vivo images obtained in a clinical setting.

The work presented in this dissertation has provided substantial insight into the mechanical properties of trabecular bone. Techniques were established to reconcile the mechanical properties obtained from in vitro testing with the true in situ behavior. We found that in vitro testing can underestimate in situ modulus and yield stress by 5-70%, and that the error systematically depended on trabecular microarchitecture. Using newly developed experimental and computational procedures, a robust methodology was also established to obtain trabecular tissue properties. Unique evidence was obtained to suggest that trabecular tissue properties may depend on anatomic site, with mean values of tissue modulus as low as 10 GPa within vertebrae and over 18 GPa for femoral bone.

In conclusion, this work provides definitive evidence to resolve several issues of contention in bone mechanics literature including the role of geometric deformations in the failure behavior of trabecular bone, and the biomechanical significance of effective tissue properties derived from micro-FE models. This dissertation has also described techniques by which predictions of bone strength and may be improved when using images at clinical-type resolutions and outlined areas of research to further advance this field of study.