The complex relationship between bone remodeling and the physical and material properties of bone

Excerpt

Bone’s fracture resistance is dependent on the amount of bone, its architectural organization, and the material properties of the matrix that compose it. Although past concentration has been on mass and geometry, there is increasing recognition that bone’s material properties play a critical role in its fracture resistance. Unlike bone mass which is determined by one feature—how much?—or architecture, which is determined by two features—amount and location—material properties are determined by a dynamic complex and multi-level set of molecular components and processes that are interdependent. This includes the materials themselves—collagen, mineral, noncollagenous proteins, and water—how they are assembled, and the nature of the interfaces between them. These properties of the material are, in turn, partly dependent on the rate of bone turnover. As turnover decreases, bone’s mean tissue age becomes older, causing the collagen to become more highly cross-linked, the mineral to accumulate and contribute to increasing homogeneity, and the tissue to become less hydrated (only partly because mineral displaces some of the water). During aging, each of these features contributes to decrease the ductility of the bone, which in turn contributes to the skeletal fragility caused by bone loss and measured by BMD. …