Preferential orientation of biological apatite crystallite in original, regenerated and diseased cortical bones

The bone mechanical function depends on both bone quantity and quality corresponding dominantly to bone mineral density (BMD: density of biological apatite) and other factors, respectively. BMD is correlated with bone strength but accounts for only 60-70% of the variance in the ultimate strength of bone tissue. Thus, new parameters representing bone quality have been investigated so far. Bone has a well-organized microstructure on the nano-scale level and is composed of mineral biological apatite (BAp) and collagen (Col) fibril, providing reinforcement and pliability, respectively. Because BAp crystallizes in an anisotropic hexagonal lattice, mechanical properties of a BAp crystallite should depend on the crystal orientation. Thus, preferential orientation of the BAp c-axis along the extended collagen fibrils in hard tissues must be closely related to the mechanical function of bone and is also utilized as a possible index for evaluating bone quality. In this study, BAp orientation was analyzed as a parameter of bone quality in hard tissues under various conditions such as original, regenerated and diseased bones. Finally, we can conclude that the degree of BAp orientation is a useful parameter to evaluate in vivo stress distribution, nano-scale microstructure and the related mechanical function, the regenerative process of the regenerated bone and to diagnose bone diseases such as osteoarthritis, etc.