pQCT measurement of bone parameters in young children: validation of technique.

Dual-energy X-ray absorptiometry (DXA) measures areal bone mineral density (BMD) and is affected by bone size. Peripheral quantitative computed tomography (pQCT) measures volumetric density and should not be affected by bone size. We hypothesized that pQCT could be used to measure geometric parameters in the tibia and that bone size, not density, would correlate with weight and height in 3 and 4 yr olds. Phantom measurements indicate that accurate results for cortical volumetric bone mineral density can be obtained at cortical thickness > 2 mm with voxel/speed sizes of 0.40/20 mm/s. Correlations between pQCT measured geometric bone parameters and phantom calculations were observed (all r > 0.96). Baseline data from an ongoing trial of 101 preschool children (53 male) were used to correlate bone parameters and anthropometrics. Total cross-sectional area, cortical area, and cortical thickness correlated with weight (r = 0.54, p < 0.001; r = 0.52, p < 0. 001; r = 0.30, p = 0.002) and height (r = 0.41, p < 0.001; r = 0.55, p < 0.001; r = 0.41, p < 0.001). Because of the small cortical thickness at this age (mean = 1.2 mm) cortical density was not analyzed. In a regression model including height and weight, weight was the only predictor of total cross-sectional area (p < 0.001); cortical thickness was predicted by height (p = 0.006). Both height (p = 0.005) and weight (p = 0.05) predicted the cortical area. In summary, pQCT accurately measures total cross-sectional area, cortical area, and cortical thickness in children age 3-4 yr.