Age- and gender-related macro- and micro-architecture changes in bone structure and implications for treatment

Bone strength, which is resistance to fracture, depends not only on the bone mass, but also on its spatial distribution (microand macroarchitecture) and the intrinsic properties of the materials that constitute the bone [1]. A particular feature of the bone is the ability to adapt its size and shape in response to mechanical loads, through the process of modeling achieved by the independent action of osteoblasts and osteoclasts. Modeling occurs principally during growth, but also in the adult, according to Wolff ’s law, in response to a mechanical load, as the use of a certain limb in a sport player, resulting in a thickening of bone cortex and an enlargement of external bone diameter, or conversely to the unloading of the skeleton, as during bed rest or space flight [2,3]. Another process, known as remodeling, allows the skeleton to maintain mechanical integrity through the constant osteoclastic resorption of damaged bone followed by osteoblast-mediated deposition and mineralization of new matrix. Overall remodeling rates average 8–10% per year in the adult [3], but individual bone sites can vary widely depending on the level of accumulated microdamage. At a macroscopic level, two types of bone can be distinguished: the cortical bone, located in the shaft of long bones and on outer surfaces of the flat bones, and the trabecular bone, found at the extremity of long bones and at the inner parts of flat bones. The two compartments differ for microand macro-architecture and speed of turnover. Bone loss starts at the bone surfaces; therefore, changes in bone mass occur earlier and more intensively in trabecular bone than in cortical [3].