Association between 3 D CT-based volumetric fat infiltration of lumbar paraspinal muscles and bone mineral density: a clinical study.
OBJECTIVE This study investigated the association between the fat infiltration rate (FIR) of lumbar paraspinal muscles-specifically the multifidus, erector spinae, and psoas major-and bone mineral density (BMD) in postmenopausal women. By examining muscular and segmental (L2-L4) adiposity variations, we aimed to identify imaging biomarkers for early osteoporosis detection and to inform integrated "bone-muscle" therapeutic strategies. METHODS A retrospective analysis was performed on 120 postmenopausal women who underwent dual-energy X-ray absorptiometry (DXA) and lumbar computed tomography (CT) between 2024 and 2025. Participants were categorized into three cohorts-normal bone mass, osteopenia, and osteoporosis-based on DXA T-scores. Demographic data, including BMI, were recorded and subsequently utilized as a covariate in the regression models to ensure robust statistical adjustment. The L2-L4 paraspinal musculature was automatically segmented in 3D using 3D Slicer software with the MuscleMap plug-in to determine the FIR for each muscle group. Data normality was assessed using Shapiro-Wilk tests, while inter-group differences were compared via one-way ANOVA or Kruskal-Wallis H tests. Correlations were quantified using Pearson or Spearman analyses. RESULTS Age was comparable across groups ( P = 0. 160 ), but BMI and average BMD differed significantly. Multifidus FIR showed a significant inverse correlation with BMD ( P < 0. 001 ). After adjusting for BMI, multifidus fat infiltration remained an independent predictor of BMD. At the segmental level, the L3 multifidus displayed the greatest inter-group variance and the strongest negative correlation with BMD ( r = -0. 689, P < 0. 001 ). CONCLUSIONS Lumbar paraspinal muscle adiposity, particularly in the L3 multifidus, is inversely associated with BMD in postmenopausal women. Consequently, L3 multifidus FIR is a statistically significant auxiliary imaging metric for proactive osteoporosis screening and the assessment of osteosarcopenia risk.