The contribution of the cortical shell and endplate to the stiffness and strength of the vertebral body is not well understood. However, several studies have suggested that the cortical shell plays an important role in the fracture strength of the whole vertebral body as bone is progressively lost from the centrum due to aging and osteoporosis (Eastell 1991, Faulkner 1991, Kurowski 1986, Silva 1997). Silva et al. (1994) concluded that prediction of cortical bone geometry using computed tomography (CT) based measurements is subject to considerable uncertainty caused by image distortion and the low ratio of image resolution of 0.25 mm/pixel to cortical shell thickness (0.09- 0.86 mm). Thus, in development of CT-based models of the vertebral body, particular attention should be paid to the details of shell modeling. The overall goal of this study was to characterize the sensitivity of whole vertebral body stiffness to cortical bone material property changes. Specifically, the objectives were: 1) to determine the effect of shell modulus on vertebral body stiffness using CT-based finite element models; 2) using experimental values of stiffness for these vertebral bodies, determine the elastic modulus for vertebral cortical bone that produces exact agreement between model and experiment; and 3) using a single mean value of modulus for the vertebral cortical bone from this calibration, quantify the error between the model prediction and experimental measurement of the stiffness for all vertebral bodies.
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