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 cortical bone cross-sectional properties of the adult radius and ulna (cross-sectional area, thickness, centroids, area moments of inertia and section 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 serial locations. Sites of significant variation of selected geometric and mineral properties along the length of each forearm bone were determined. Our results show that interpolation of CT measurements made at 10 and 30% of the radial length in the radius and 30 and 90% of the radial length in the ulna can provide approximate geometric values over the 10-90% region. This information can be used to develop a protocol using the fewest sites to clinically assess changes in forearm bone geometry. Regression analyses did not show significant linear relationships between geometric properties and apparent cortical ash density. Thus, CT derived geometric properties are not helpful in estimating the extent of changes in bone density. Area moment of inertia results suggest 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, whereas the latter is due to the relatively small magnitude of cross-sectional moments along the ulnar shaft as compared to the proximal or distal ends. This is consistent with fracture patterns observed clinically when a single forearm bone is fractured: Galeazzi fracture of the radius and nightstick fracture of the ulna.