ESTIMATION OF STRUCTURAL AND GEOMETRICAL PROPERTIES OF CORTICAL BONE BY COMPUTERIZED-TOMOGRAPHY IN 78-YEAR-OLD WOMEN

The structural and geometrical properties of the tibia shaft were inve stigated at two sections by means of computerized tomography (CT) in 7 8-year-old women with high (n = 19) and low (n = 17) calcaneal bone mi neral density (BMD, g/cm(3)) previously measured by I-125-photon absor ption. The high BMD group had a 20-21% higher tibial BMD and 9-12% hig her bone cross-sectional area than was observed in the low BMD group. The distribution of bone mass indicated that the low BMD group had los t bone mainly from the endosteal surface, especially in the anterior p art of the tibia. However, both groups had a similar basic pattern of mass distribution at the measured sections. The high BMD group had hig her moments of inertia at the upper section than the low BMD group. Th e differences between the groups were more pronounced when only the hi gh density areas were included. At the lower section, the differences between the groups also appeared significant at the high density level s. There were no group differences in the area moments of inertia. The results suggest that the true distribution of bone mass should be tak en into account in determining the moments of inertia. In the tibia, d etermination of the cross-sectional mass distribution of bone combined with BMD should have a better discriminatory capability than BMD only in studying bone strength and fracture risk.