Effects of architecture on microdamage susceptibility in trabecular bone

Trabecular architecture plays an important role in trabecular bone biomechanics. The objectives of this dissertation were to investigate the effects of architecture on microdamage susceptibility and the failure mechanisms in trabecular microstructures using computational methods.

Direct prediction of microdamage by computational modeling is challenging. Since the Weibull probabilistic model did not improve the ability of computational models to predict damage, the morphology, number, and mean volume of the predicted yielded regions were studied for overloading of trabecular bone specimens along two orthogonal directions. During on-axis overloading, the expanding compressively yielded regions and the increasing number of tensilely yielded regions indicate the importance of vertical trabeculae and stress redistribution, respectively. During transverse overloading, the simultaneous increases in the number and mean volume of both the compressively and tensilely yielded regions suggest buckling of the struts. In a following study, an Individual Trabeculae Segmentation (ITS) technique was exploited to label the type and orientation of the predicted failed trabeculae. For both on-axis and transverse overloading, most of the yielding occurred in longitudinal plates. However, the primary loading mode was axial compression with superposed bending for on-axis loading in contrast to bending for transverse loading. In addition, the yielding mode of plates does not depend on their orientation relative to the loading direction, which is different from rods, being compressed along the loading direction and bent perpendicular to the loading direction. When yielding with respect to trabecular type and orientation was compared to experimental measures of microdamage in the same specimens, only the proportion of the predicted tissue yielding in longitudinal rods was correlated with the measured microcrack density. This suggests that although longitudinal plates provide most of the mechanical support, longitudinal rods determine the whole structure's susceptibility to microdamage formation.

In the end, effects of the tissue constitutive model and geometric nonlinearity on the amount and location of the predicted yielding were compared between a bilinear principal-strain tissue constitutive model and the fully nonlinear Drucker-Lode tissue constitutive model. Results from the investigations confirm that using a simple bilinear model that omitted geometric nonlinearity should not compromise the conclusions of this dissertation for the dense plate-like specimens used in the study.Overall, this study provided a quantitative way to look at the role of trabecular architecture in microdamage susceptibility and explored the yielding modes of individual trabeculae during microdamage formation.