CORTICAL AND TRABECULAR BONE CONTRIBUTE STRENGTH TO THE OSTEOPENIC DISTAL RADIUS

Fractures of the distal radius are common, especially in postmenopausa l women, and their prevalence increases with age. Knowledge of the fac tors that increase the risk of fracture in this metaphyseal region wou ld have predictive and therapeutic implications. Of particular interes t in this study were (a) the relative contributions of cortical and tr abecular bone to the strength of the distal radius and (b) the best ra diographic features to use as strength indicators. In 21 forearms from fresh cadavera (median age at the time of death, 75 years), single ph oton absorptiometry and quantitative computed tomography were used to determine bone mineral content (BMC), density (BMC/W), and cross-secti onal 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 fa ll on the outstretched hand. Twelve of the 17 tested specimens sustain ed a fracture of the distal radius, and five sustained a fracture of t he scaphoid. In the group of fractures of the distal radius, we found the cross-sectional area and moment of inertia of the cortical shell a t the metaphyseal site to be better correlates of strength than the tr abecular area and trabecular moment. In contrast, strength correlated much better with trabecular density than with cortical density. Overal l, the best correlates of strength were the BMC and BMC/W at either th e distal or proximal site. On balance, these results suggest that the thin cortical shell contributes substantially more to the mechanical s trength of the distal radius than has been commonly appreciated.