Increased Collagen Mineralization Affects the Yield Stress But Not the Yield Strain in Cortical Bone of Rats: Implications for Age-Related Tissue Embrittlement

It has been well documented that the fracture susceptibility of cortical bone increases significantly with age [1]. Although the age-related decline in the fracture resistance of the cortical bone is attributed to reduced bone quantity; a substantial overlap in the bone mass of normal subjects and those sustaining fractures suggests that bone mass alone does not identify the fracture risk on an individual basis [2]. Therefore, the conceptual framework should be improved to include bone quality measures in addition to bone quantity to refine fracture risk assessment. In this study, Raman microspectroscopy was used to assess two key variables of bone tissue quality in aging rat cortical bone: the relative amount of mineral with respect to the amount of collagen (i.e. collagen mineralization) and the mineral crystallinity (i.e. size and stoichiometric perfection of mineral crystals). In this regard the first aim of this study was to investigate age-related changes in the extent of mineralization of collagen fibers and to test its relationship to elastic deformability of cortical bone tissue. The second aim of the study was to investigate age-related changes in the mineral crystallinity and to test its relationship to elastic deformability of cortical bone tissue. The first hypothesis of this study is that both collagen mineralization and mineral crystallinity will increase with age. The second hypothesis of this study was that age-related changes in compositional properties will compromise the elastic deformation capacity of cortical bone tissue.