Bone is a composite material consisting of hydroxyapatite (HA) crystals deposited in an oriented manner on a collagen backbone. The arrangement of the mineral and organic phases provides bone tissue with the appropriate strength, stiffness, and fracture resistance properties required to protect vital internal organs and maintain the shape of the body. A remarkable feature of bone is the ability to alter its properties and geometry in response to changes in the mechanical environment. Under normal physiologic loading conditions, non-traumatic bone microdamage occurs locally and the damaged region is repaired and replaced through the coordinated process of bone remodeling. In fact, bone microdamage has been suggested to be an important stimulus in providing spatial regulation of bone remodeling activity [1-3].

While moderate levels of bone microdamage may play an important role in maintaining bone structural integrity, in cases of mechanical overload (trauma), metabolic bone diseases, or aging, bone can no longer successfully adapt to its environment, increasing its fragility. The accumulation of excessive damage can result in degradation of mechanical properties leading to bone failure (i.e. fracture). Understanding the underlying mechanisms of bone damage may provide strategies for prevention and treatment of bone fragility diseases such as osteoporosis. To elucidate the mechanisms of bone microdamage, this research project developed a specimen-specific approach that integrated 3D imaging, histological damage labeling, image registration, and image-based finite element analysis to correlate microdamage events with microstructural stresses and strains under compressive loading conditions. By applying this technique to different ages of bone, this research study has provided an improved understanding of the relationship between the local mechanical environment and microdamage and may provide a new measure of changes in bone quality associated with the progression or treatment of skeletal fragility.