Cortical and trabecular bone contribute strength to the osteopenic distal radius.

Fractures of the distal radius are common, especially in postmenopausal women, and their prevalence increases with age. Knowledge of the factors that increase the risk of fracture in this metaphyseal region would have predictive and therapeutic implications. Of particular interest in this study were (a) the relative contributions of cortical and trabecular bone to the strength of the distal radius and (b) the best radiographic features to use as strength indicators. In 21 forearms from fresh cadavera (median age at the time of death, 75 years), single photon absorptiometry and quantitative computed tomography were used to determine bone mineral content (BMC), density (BMC/W), and cross-sectional properties of the radius at distal and midshaft sites. Mechanical testing of the forearms then was used to determine the ultimate force and energy to cause the type of fracture that might be caused by a fall on the outstretched hand. Twelve of the 17 tested specimens sustained a fracture of the distal radius, and five sustained a fracture of the scaphoid. In the group of fractures of the distal radius, we found the cross-sectional area and moment of inertia of the cortical shell at the metaphyseal site to be better correlates of strength than the trabecular area and trabecular moment. In contrast, strength correlated much better with trabecular density than with cortical density. Overall, the best correlates of strength were the BMC and BMC/W at either the distal or proximal site. On balance, these results suggest that the thin cortical shell contributes substantially more to the mechanical strength of the distal radius than has been commonly appreciated.