Potential physiological determinants of diagnostic discordance between an MRI-derived lumbar vertebral bone quality score and DXA T-scores.
OBJECTIVE MRI-derived vertebral bone quality (VBQ) scores estimate vertebral marrow-related bone quality on T1-weighted imaging and may complement dual-energy X-ray absorptiometry (DXA) in spine patients. Discordance between VBQ and DXA is common, particularly in the lumbar spine, where degenerative changes may bias DXA measurements. This study aimed to identify physiological determinants associated with lumbar VBQ-DXA discordance. METHODS We retrospectively included 266 consecutive adults with preoperative lumbar MRI and DXA performed within 6 months before surgery. Lumbar VBQ was calculated as the ratio of the median T1 signal intensity of the L1-L4 vertebral bodies to cerebrospinal fluid signal intensity. Correlations between VBQ, DXA-derived T-scores, and clinical and laboratory variables were examined, and multivariable regression was used to identify independent determinants of VBQ. Concordance and discordance phenotypes were defined using the lower T-score from the lumbar spine and femoral neck (DXA-normal: ≥ -1.0; DXA-abnormal: < -1.0) and an ROC-derived VBQ threshold. RESULTS VBQ was positively correlated with age (r = 0.706, p < 0.001) and moderately inversely correlated with both lumbar spine T-score (r = -0.396, p < 0.001) and femoral neck T-score (r = -0.374, p < 0.001). ROC analysis showed moderate discrimination of DXA-defined osteoporosis, with an AUC of 0.728. At the cutoff of 2.685, sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy were 65.1%, 70.8%, 30.1%, 91.3%, and 69.9%, respectively. In multivariable regression, triglycerides (β = 0.397, p = 0.003), very low-density lipoprotein cholesterol (β = 1.325, p = 0.002), glycated albumin (β = 0.184, p = 0.003), and conjugated bilirubin (β = 0.162, p = 0.004) were independent determinants of VBQ. The DXA-normal/VBQ-abnormal phenotype showed enrichment of this TG/VLDL-C/GA/CB metabolic pattern. CONCLUSIONS Lumbar VBQ-DXA discordance is associated with a physiological signature characterized by triglyceride-rich lipoproteins, glycation burden, and conjugated bilirubin. VBQ may complement DXA by identifying metabolically vulnerable, marrow-related bone quality changes that are not fully captured by DXA-derived T-scores.