The mechanical properties of
vertebral bone have been widely studied with the ultimate goal of improving fracture risk prediction. However, the mechanical interaction between the cortical shell and the trabecular core is not well understood. The objective of this study was to investigate this interaction and to determine what effect it has on the ultimate strength of the whole
bone. This objective was achieved by compression testing rapid prototype (RP) models of cylindrical
trabecular bone cores, with and without an integral surrounding shell and incorporating increasing levels of artificially induced
bone loss. Corresponding finite element (
FE) models were generated and the load sharing of the shell and trabecular core was analysed under linear elastic loading conditions. The results of the physical RP model tests and corresponding
FE analyses indicated that there was a reinforcing effect between the cortical shell and the trabecular core for all models tested and that the reinforcing effect became relatively more important to the ultimate strength of the whole
bone as the
bone volume fraction of the trabecular core decreased. It was found that two mechanisms contributed to the reinforcing effect: (i) load transfer from the highly stressed shell into the connecting outer
trabeculae of the core for the shelled model. This did not occur for the un-shelled model where the load dropped off at the outer unsupported
trabeculae; (ii) the stiffening effect on the shell due to the support provided by the connecting struts of the trabecular core, which serves to inhibit bending and buckling behaviour in the shell under compression loading. It was found that the stiffening on the shell was the more dominant contributor to the overall reinforcing effect between the shell and the trabecular core.
