Changes in Structure of Human Bone with Age

Abstract

THE pliability of human bone decreases with increasing age, and the incidence of bone fracture increases after about 35 years of age. These changes indicate that some structural changes occur in bone over a lifetime. Much work has been done on the correlation between the histological components of bone and its physical properties, and their variation with age, but contradictory conclusions have been drawn1,2. No attempt seems to have been made to correlate the physical properties of bone with the physical and chemical nature of bone mineral, although it has been claimed that fracture occurs chiefly at “cement lines”2. Because the chemical nature of bone mineral, that is apatite, does not undergo any appreciable change during a lifetime, it can be inferred that the changes probably occur in the physical properties of the apatite crystals; for example, size and shape or their relative arrangement in space. Robinson and Watson3 claimed from their electron microscopy that crystallites of bone apatite increase in size with age. But their experimental technique—sectioning of bone with a glass knife, use of silica-coated collodion-covered grids, and subsequent deliberate heating of the specimen grids—makes their results difficult to interpret, especially in view of recent observations that the process of sectioning may deform and/or shatter the crystallites4. Robinson and Watson did not try to correlate their observations with the physical properties of bone, although they observed that senile bone was difficult to section.