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The mechanical behavior of trabecular bone depends on the internal bone structure as well as the load applied. Mechanical stresses and strains influence the modeling process and subsequently the structure and strength of the bone. Although the basic concepts of adaptive bone remodeling are generally accepted, the mathematical laws relating bone remodeling to the stress/strain relations are still under investigation. The aim of this project was to develop an algorithm which allows simulation of the response of the trabecular bone is age-related bone loss and to determine the biomechanical consequences of such a response based on realistic 3D models of the trabecular microstructure. Today, such models can be generated directly using micro-computed tomography ((mu) CT). For the purpose of the study, a compact fan-beam type tomograph was used, also referred to as desktop (mu) CT, providing a nominal isotropic resolution of 14 micrometers . Two groups of seven trabecular bone specimens were measured including specimens from pre- menopausal and post-menopausal women respectively. In order to control bone loss over age, a novel algorithm to simulate bone resorption and adaptive process was developed. The algorithm, also referred to as simulated bone atrophy, generates a set of microstructural models, iteratively derived from the original 3D structure. Simulated bone atrophy was used to 'age-match' the first and the second group incorporating an underlying realistic time-frame for the simulation. Using quantitative bone morphometry and 3D animation tools, the changes in bone density and bone architecture could be monitored in the progress of age- related bone loss over a total observation time of 28 years. The structures at the end-point of the simulations were then compared qualitatively and quantitatively to the structures of the post-menopausal group directly assessed by (mu) CT. The results suggest the possibility of transforming 'normal' to osteopenic' bone on a microstructural level resulting in realistic bone models similar in appearance and structural properties when compared to the post-menopausal group. In the future, the assessment of the biomechanical competence of microstructural bone in the progress of adaptive bone remodeling might result in an improved prospective prediction of individual bone strength as an indicator for fracture risk in patients predisposed to osteoporosis.
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