Quantitative analysis of modified functional muscle–bone unit and back muscle density in patients with lumbar vertebral fracture in Chinese elderly men: a case–control study

Objectives: Bone mineral density (BMD) is associated with muscle mass and quality, but little research has been done on functional muscle–bone unit and back muscle density in patients with lumbar vertebral fracture. This study used the “modified functional muscle–bone unit” concept and measured back muscle density to investigate muscle–bone interaction difference between the fracture and control group. Methods: This was a case–control study. A total of 52 elderly male patients (mean age 75 years) with lumbar vertebral fracture (cases) and 52 control healthy subjects were enrolled. Cross-sectional area (CSA) and density of paravertebral muscle were measured in quantitative computed tomography (QCT) images to represent the muscle mass, while the bone mineral density measured by QCT was used to represent the bone mass. The modified functional muscle–bone unit was calculated as the value of volumetric BMD divided by muscle area. Results: People with vertebral fractures reported significantly lower values in the cross-sectional area and density of paravertebral muscle compared to control group. In the multivariate analysis, BMD (odds ratio, OR = 0.929; 95% confidence intervals, CIs 0.888–0.971), erector muscle density (OR = 0.698; 95% CI 0.547–0.892), and summated muscle CSA (OR = 0.963; 95% CI 0.93–0.991) were independent protective factors for the presence of a fracture. BMD resulted significantly and moderately associated with cross-sectional area and density of paravertebral muscle (r = 0.329–0.396). Conclusions: There were significant differences between the modified functional muscle–bone unit and back muscle density between the fracture group and control group in elderly men. Lower BMD, loss of muscle mass and density are associated with increased presence of the lumbar vertebral fracture.