The role of cortical bone and its microstructure in bone strength.

Bone's mechanical competence and its fragility in particular depend to a certain extent on the structure and microstructure of the cortical bone compartment. Beyond bone mineral density (BMD) and bone mineral content, a variety of other features of cortical bone contribute to whole bone's resistance to fracture. Structural properties of cortical bone most commonly employed as surrogate for its mechanical competence include thickness of the cortex, cortical cross-sectional area and area moment of inertia. But microstructural properties such as cortical porosity, crystallinity or the presence of microcracks also contribute to bone's mechanical competence. Microcracks in particular not only weaken the cortical bone tissue but also provide an effective mechanism for energy dissipation. Bone is a damageable, viscoelastic composite and most of all a living material capable of self-repair and thus exhibits a complex repertoire of mechanical properties. This review provides an overview of a variety of features of cortical bone known to provide mechanical competence and how these features may be applied for fracture risk prediction.