The effects of composition, structure and age on the torsional properties of the human radius.

A standard site in the distal shaft of the radius is commonly used to monitor the skeletal status of aging individuals by photon absorptiometry. Since the adjacent metaphysis of this bone is a common site for fractures, it is important to know whether bone mineral content (BMC) is a good indicator of mechanical integrity. In concert with previous studies, the BMC of the scan site declined significantly (p less than 0.005) with age in women but in men showed no change to age 90. In spite of the loss of BMC, there was no decrease in torsional rigidity in women. In men torsional rigidity increased significantly (p less than 0.05) with age even though BMC did not change. Thus, measurements of BMC alone do not adequately reflect the mechanical integrity of a clinically significant skeletal site, and assessment of skeletal health based on such criteria may be misleading.