Application of high-resolution skeletal imaging to measurements of volumetric BMD and skeletal microarchitecture in Chinese-American and white women: explanation of a paradox.

Asian women have lower rates of hip and forearm fractures despite lower areal BMD (aBMD) by DXA compared with white women and other racial groups. We hypothesized that the lower fracture rates may be explained by more favorable measurements of volumetric BMD (vBMD) and microarchitectural properties, despite lower areal BMD. To address this hypothesis, we used high-resolution pQCT (HRpQCT), a new method that can provide this information noninvasively. We studied 63 premenopausal Chinese-American (n = 31) and white (n = 32) women with DXA and HRpQCT. aBMD by DXA did not differ between groups for the lumbar spine (1.017 +/- 0.108 versus 1.028 +/- 0.152 g/cm(2); p = 0.7), total hip (0.910 +/- 0.093 versus 0.932 +/- 0.134 g/cm(2); p = 0.5), femoral neck (0.788 +/- 0.083 versus 0.809 +/- 0.129 g/cm(2); p = 0.4), or one-third radius (0.691 +/- 0.052 versus 0.708 +/- 0.047 g/cm(2); p = 0.2). HRpQCT at the radius indicated greater trabecular (168 +/- 41 versus 137 +/- 33 mg HA/cm(3); p = <0.01) and cortical (963 +/- 46 versus 915 +/- 42 mg HA/cm(3); p < 0.0001) density; trabecular bone to tissue volume (0.140 +/- 0.034 versus 0.114 +/- 0.028; p = <0.01); trabecular (0.075 +/- 0.013 versus 0.062 +/- 0.009 mm; p < 0.0001) and cortical thickness (0.98 +/- 0.16 versus 0.80 +/- 0.14 mm; p < 0.0001); and lower total bone area (197 +/- 34 versus 232 +/- 33 mm(2); p = <0.001) in the Chinese versus white women and no difference in trabecular number, spacing, or inhomogeneity before adjustment for covariates. Similar results were observed at the weight-bearing tibia. At the radius, adjustment for covariates did not change the direction or significance of differences except for bone, which became similar between the groups. However, at the tibia, adjustment for covariates attenuated differences in cortical BMD and bone area and accentuated differences in trabecular microarchitecture such that Chinese women additionally had higher trabecular number and lower trabecular spacing, as well as inhomogeneity after adjustment. Using the high-resolution technology, the results provide a mechanistic explanation for why Chinese women have fewer hip and forearm fractures than white women.