Vertebral cortical bone mass measurement by a new quantitative computer tomography method: correlations with vertebral trabecular bone measurements.

Previous studies comparing axial and appendicular skeleton have shown that trabecular bone loss is greater than cortical bone loss. However, whether the same difference exists between the trabecular and the cortical compartments of the vertebral body remains to be determined. In this study, we used quantitative computer tomography (QCT) to simultaneously measure the cortical rim of the vertebral body as well as trabecular bone. In 99 Caucasian women (mean age 53.8 +/- 13.0 years, range 26-79 years) we found a significant correlation between cortical mineral content (BMCC) and both single (SE) and dual energy (DE) trabecular mineral content (BMCT) (r = 0.62, P less than 0.0001 for both regressions). The cross-sectional rates of bone loss per year were 1.32%, 1.16%, and 0.59% for SE-BMCT, DE-BMCT, and BMCC, respectively. BMCC decreased at a rate that was 45-51% that of SE-BMCT and DE-BMCT, respectively. Our results indicate that (1) QCT may provide a useful means to selectively measure cortical density in vertebral bodies; (2) the decrease of cortical density over time in the spine appears to have been underestimated previously by extrapolation from appendicular bone measurements; (3) because measurements of the entire vertebral body (exclusive of the posterior elements) may provide information that is more representative of spine changes with age, a measurement that includes both areas might be more useful than one measuring only the trabecular region.