Bone structure and fracture risk: Do they go arm in arm?

Abstract

increased cortical and trabecular thickness and greater cortical density at both the distal radius and the distal tibia. (12,13) In the current study, 29 Chinese-American and 68 white postmenopausal women were evaluated. Areal bone mineral density (aBMD) at the spine, hip, and radius was measured using dualenergy X-ray absorptiometry (DXA), and bone microstructure at the distal radius and tibia was assessed using HR-pQCT. As expected, the Chinese-American women were shorter and weighed less than the white women. Surprisingly, however, aBMD was similar between the two groups at all skeletal sites. Postmenopausal Chinese-American women had approximately 10% smaller bone cross-sectional area but 5% to 6% higher cortical density and 16% to 18% higher cortical thickness than whites. Chinese-American women also had fewer trabeculae at the distal radius and fewer but thicker trabeculae at the distal tibia compared with whites. Differences in bone cross-sectional area were attenuated somewhat after adjusting for the shorter stature and lower weight of the Chinese-American women, whereas differences in cortical and trabecular thickness were largely unaffected. The net result of these differences in bone morphology, evaluated by finite-element analysis (FEA), showed similar compressive stiffness in the two groups, suggesting that the smaller cross-sectional area in Chinese-American women was compensated for by their increased cortical and trabecular thicknesses. The study provides novel insights into differences in bone structure by ethnicity, yet several issues should be considered when interpreting the results, including (1) the modest sample size, (2) the limitations of HR-pQCT measurements and assumptions used for derivation of some microarchitecture features, and (3) lack of information on tissue material properties. The authors examined a relatively small convenience sample of only 29 Chinese-American subjects who were, on average, 2 years younger and tended to be closer to the menopause than the white women. After adjusting the analyses for age and body mass index (BMI), the strength of some of the ethnicity-related differences was attenuated, although most of the differences