Correlations between photon absorption properties and failure load of the distal radius in vitro.

The bone mineral content (BMC) and cross-sectional properties of cadaveric radii were assessed by single photon absorptiometry (SPA). A new multiple-angle scanning technique was used in conjunction with SPA to measure the area and moments of inertia of the radial cross section in intact forearms. The radii of the same forearms were then broken in a failure test to simulate a fall on the outstretched arm. Colles' fracture was produced in 16 of 18 radii tested. The BMC divided by the bone width, which is called bone mineral density (BMD) in clinical applications, did not correlate with the load at failure in cadaveric forearms. The BMC alone did correlate significantly with failure load (r2 = 0.62), and the cross-sectional properties gave the best correlation with failure load in a sequential multiple regression (r2 = 0.80). We conclude that if SPA is to be used in clinical studies to predict risk of radial fracture or of fractures at remote skeletal sites, then BMC should be used rather than BMD. An even better indicator of radial bone strength than BMC would be a biomechanical parameter derived from the cross-sectional area and moments of inertia, which can be obtained from multiple-angle SPA.