Changes in Bone Remodeling Rate Influence the Degree of Mineralization of Bone Which is a Determinant of Bone Strength: Therapeutic Implications

Abstract

Bone strength depends on the volume of bone matrix, the bone microarchitecture, and also on the level of bone tissue mineralization. In addition to the amount of bone matrix, the degree of mineralization of bone tissue (DMB) can strongly influence bone strength and the bone mineral density (BMD) measured by dual energy X-ray absorptiometry (DXA). DMB is known to vary over microscopic regions with the age of the basic structure units (BSUs), the recently deposited ones being much less calcified than the older ones. During bone remodeling, after bone resorption, bone formation is a multi-step process. Following its deposition, the new matrix begins to mineralize after about 5 to 10 days from the time of deposition and the linear rate of thisprimary mineralizationcan be measured directly in vivo using double tetracycline labeling. After full completion of the BSUs (osteons in cortical bone or cancellous packets) asecondary mineralizationbegins. This process consists of a slow and gradual maturation of the mineral component, including an increase in the amount of crystals and/or an augmentation of crystal size toward their maximum dimensions. The secondary mineralization progressively augments the mineral content of bone matrix deposited during primary mineralization, the latter representing only about 50% of the maximum degree of mineralization obtained at the end of the secondary mineralization phase.