Ethnic differences in skeletal structure may relate to differences in hip fracture risk in Chinese and Caucasian populations. Two dimensional mass, size and structural mechanics were compared in the two populations.

Quantitative CT derived geometric variables were compared in age-matched community derived female populations, 196 Beijing-Chinese 76.5±4.8 (mean±SD) years and 237 Perth-Caucasians 77.1±5.0 years. These included Scanned Area (A), Periosteal Width (W), Bone Mineral Content (BMC), aBMD, Bone Cross-sectional Area (bCSA), Section Modulus (Z) and Buckling Ratio (BR). Assumption-free measures included, Sigma (s), related to the distribution of bone in the scanned image previously identified as a predictor of hip fracture, and Delta (d), the center-of-mass displacement from the geometric-center.

Compared to Beijing-Chinese, Perth-Caucasians were heavier (Beijing-Chinese: 58.7±11.8; Perth-Caucasians: 66.1±11.0 kg), taller (154.9±16.7 vs 158.9±6.0 cm) and had higher BMC, A, and W. After adjustment for frame size BMC was not significantly different but W remained higher in Perth-Caucasians. Differences in variables aBMD, Z, BR and s favored higher resistance to failure with Beijing-Chinese before and after adjustment for frame size. d was similar in both populations; bCSA was higher in Beijing-Chinese before adjustment for frame size but not after.

Bone mass differences in two populations were related to frame size differences. However FN width remained smaller in Beijing-Chinese suggesting effects of local genetic and environmental factors. In Beijing-Chinese participants compared to Perth-Caucasians internal bone distribution suggests increased resistance to deformation if exposed to same force that may, in-part, relate to reduced incidence of hip fracture in Beijing-Chinese.