The osteon: the micromechanical unit of compact bone.

The research techniques available for investigation of secondary osteons in human bone enable establishment of their biological composition and quantification of their mechanical properties. Further, the data generated through current research techniques facilitate studies on the significance of osteons in normal and pathological conditions, including via multi-scale modeling conducted with a view of building realistic models of virtual bone, suitable for applications from orthopaedic challenges to endocrine disorders. The understanding of the biomechanical function of the osteon requires clarification of the molecular-cellular processes that form, maintain and remodel the osteon and affect the mechanical function. In turn, the mechanical function affects the biology of the osteon. In retrospective, the investigation of osteons has focused on the unraveling of the complex combination of elementary components to discern the major factors that define the mechanical behavior. The micro-structural environment that leads to macroscopic fracture remains unclear. Arrangement, distribution and quality of the elementary components may participate in fracture risk. The latest results underline the fundamental role of the orientation of collagen type I and of carbonated hydroxyapatite crystallites.