Micromorphological characterisation of normal human bone surfaces as a function of age.

Endosteal surfaces of human bone specimens, principally from the sixth rib, from subjects ranging in age from seven weeks to 87 years were studied using the secondary electron imaging mode in the scanning electron microscope. Specimens were examined after the removal of cells only, or after the removal of cells and organic matrix. Morphological differences made it possible to identify the age group to which a specimen belonged. The most obvious of these was the ratio of active to resting bone surfaces, which collagen matrix which was deposited at endosteal surfaces was different in the different age groups. In neonates, collagen was organised as a parallel fibred continuum. It was present in more discrete bundles in adults, although these still branched and anastomosed with one another. The bundles were parallel over limited domains which described large angles with respect to one another. The conformation of resorbed surfaces indicated that the behaviour pattern of osteoclasts changes with age. Shallow gutters, or annular zones around resorption bays were most common in neonates. The elongation ratio of resorption tracks was greatest in infants and juveniles, indicating that osteoclast translocation was greatest during resorption at these ages. The texture of the floors of resorption bays was smooth in specimens from subjects up to 13 years, while in adults the collagen fibre bundle organisation in the resorbed tissue was often visible. This difference may reflect a more equal mineralization in the ground substance and collagen compartments of the bone matrix in children than in adults.