The accurate relationship between spine bone density and bone marrow in humans

Abstract

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 (vBMD_ESPcorr) and BMAT corrected vBMD (vBMD_BMATcorr) 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 vBMD_BMATcorr 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.

Keywords: BMD; BMD accuracy errors; Bone marrow adipose tissue; Chemical shift encoded MRI; QCT.