Options for bone aging with the microscope

The skeletons of all large living verebrates undergo bone-specific ontogenetic changes in the numbers and distributions of cells which secrete new calcifiable collagen matrices (osteoblasts) and which resorb preexisting bone matrix (osteoclasts). The numbers and activities of these cells, which function via tissue remodeling to maintain the external and internal morphology of bones, are also constrained by nutritional and endocrinological influences. Investigators concerned with the practical problem of aging intact and fragmentary archaeological bone specimens, and possibly identifying frank evidence of metabolic bone disease, are denied direct access to information about cell population kinetics. The cells are not preserved. Nonetheless, age-related changes in the microscopic structure and organization of bone in contemporary populations present some useful endpoints which can be applied to this problem. In this paper, microscopic techniques which have been applied to this problem are reviewed, and the range and utility of structures in bone which form as a consequence of bone remodeling activity are examined. The major problems in microscopic bone aging studies relate to sampling site speciticity since normative values for each parameter in every human and primate skeletal element throughout the life span are not available. Secular changes should also be considered.