Finite element analysis of vertebral body mechanics with a nonlinear microstructural model for the trabecular core

In this study, a finite element model of a vertebral body was used to study the load-rolebearing of the two components (shell and core) under compression. The model of the vertebralbody has the characteristic kidney shape transverse cross section with concave lateralsurfaces and flat superior and inferior surfaces. A nonlinear unit cell based foam modelwas used for the trabecular core, where nonlinearity was introduced as coupled elastoplasticbeam behavior of individual trabeculae. The advantage of the foam model is thatarchitecture and material properties are separated, thus facilitating studies of the effectsof architecture on the apparent behavior. Age-related changes in the trabecular architecturewere considered in order to address the effects of osteoporosis on the load-sharingbehavior. Stiffness changes with age (architecture and porosity changes) for the trabecularbone model were shown to follow trends in published experimental results. Elasticanalyses showed that the relative contribution of the shell to the load-bearing ability of thevertebra decreases with increasing age and lateral wall curvature. Elasto-plastic (nonlinear)analyses showed that failure regions were concentrated in the upper posteriorregion of the vertebra in both the shell and core components. The ultimate load of thevertebral body model varied from 2800 N to 5600 N, depending on age (architecture andporosity of the trabecular core) and shell thickness. The model predictions lie within therange of experimented results. The results provide an understanding of the relative role ofthe core and shell in vertebral body mechanics and shed light on the yield and post-yieldbehavior of the vertebral body.