The Orientation Distribution of Apatite Crystals Accounts for Variability in the Elastic Anisotropy of Human Cortical Bone Tissue

摘要

Elastic constants for cortical bone tissue have been correlated with the apparent tissue density, mineral density, and tissue porosity [1-4], but the little data that exists has indicated a weak or no relationship between these structural parameters and the elastic anisotropy [4,5]. A micromechanical model accounting for seven structural parameters across multiple length scales identified the bone mineral orientation distribution to be the most significant structural parameter governing the elastic anisotropy of cortical bone [6].rnBone mineral is a carbonated apatite exhibiting plate-like crystals elongated in the hexagonal c-axis along the [001] crystallographic direction. The elongated shape of the apatite crystals, and to a lesser extent the anisotropic elastic constants of the crystals themselves, imparts increased stiffness along the direction of preferred orientation. Cortical bone exhibits a c-axis preferred orientation along directions of principal stress (Fig. 1), which can be measured by quantitative texture analysis using x-ray diffraction [6-8]. Therefore, the objective of this study was to correlate the elastic anisotropy with the orientation distribution of apatite crystals in human cortical bone specimens.