LAUSR

CONTEXT The accuracy of QCT measurements of lumbar spine trabecular volumetric bone mineral density (vBMD) is decreased due to differences in the amount of bone marrow adipose tissue (BMAT). OBJECTIVE To correct vBMD measurements for differences in marrow composition and investigate the true relationship between vBMD and BMAT. DESIGN Cross-sectional study. SETTING University teaching hospital. PARTICIPANTS Healthy Chinese subjects (233 women, 167 men) aged between 21 and 82 years. MAIN OUTCOME MEASURES vBMD and BMAT were measured using QCT (120 kV) and chemical shift-encoded MRI of the L2-L4 vertebrae. vBMD measurements were standardized to the European Spine Phantom (ESP) and corrected for differences in BMAT. Linear regression was used to analyze BMAT, ESP adjusted vBMD (vBMDESPcorr) and BMAT corrected vBMD (vBMDBMATcorr) against age and corrected vBMD against BMAT. RESULTS BMAT in the L2-L4 vertebral bodies increased with age in both sexes, with a faster rate of change in women compared with men (0.54%/year vs. 0.27%/year, P < 0.0001). After vBMD measurements were corrected for BMAT there were statistically significant changes in the slope of the regression line with age in both sexes (women: -3.00 ± 0.13 vs. -2.57 ± 0.11 mg/cm3/year, P < 0.0001; men: -1.92 ± 0.15 vs. -1.70 ± 0.14 mg/cm3/year, P < 0.0001). When vBMDBMATcorr was plotted against BMAT, vBMD decreased linearly with increasing BMAT in both sexes (women: -3.30 ± 0.18 mg/cm3/%; men: -2.69 ± 0.25 mg/cm3/%, P = 0.048). CONCLUSION Our approach reveals the true relationship between vBMD and BMAT and provides a new tool for studying the interaction between bone and marrow adipose tissue.