CROSS-SECTIONAL GEOMETRICAL PROPERTIES AND BONE-MINERAL CONTENTS OF THE HUMAN RADIUS AND ULNA

The mechanical strength of the human radius and ulna depends on their geometrical and material properties. This study quantifies the cortica l bone cross-sectional properties of the adult radius and ulna (cross- sectional area, thickness, centroids, area moments of inertia and sect ion moduli) using computerized tomographic (CT) scanning coupled with image processing along the lengths of eight human cadaveric forearms. Bone mineral mass and apparent ash density were also quantified at ser ial locations. Sites of significant variation of selected geometric an d mineral properties along the length of each forearm bone were determ ined. Our results show that interpolation of CT measurements made at 1 0 and 30% of the radial length in the radius and 30 and 90% of the rad ial length in the ulna can provide approximate geometric values over t he 10-90% region. This information can be used to develop a protocol u sing the fewest sites to clinically assess changes in forearm bone geo metry. Regression analyses did not show significant linear relationshi ps between geometric properties and apparent cortical ash density. Thu s, CT derived geometric properties are not helpful in estimating the e xtent of changes in bone density. Area moment of inertia results sugge st that the junction of the middle and distal third of the radius, and the ulnar shaft region may have increased vulnerability to fractures. The former is likely due to the change in moment of inertia values, w hereas the latter is due to the relatively small magnitude of cross-se ctional moments along the ulnar shaft as compared io the proximal br d istal ends. This is consistent with fracture patterns observed clinica lly when a single forearm bone is fractured: Galeazzi fracture of the radius and nightstick fracture of the ulna.