Relationship between Vertebral Instability and the Cross-Sectional Area of Lumbar Muscles in Postmenopausal Acute Osteoporotic Vertebral Fractures

INTRODUCTION: Vertebral instability (VI) in osteoporotic vertebral fractures (OVFs) varies from mild to severe. The relationship between the VI of OVFs and independent factors, such as bone mineral density (BMD) and lumbar muscle volume, is unclear. This study aimed to investigate whether BMD and the cross-sectional area (CSA) of lumbar muscles are related to VI in OVFs. METHODS: On the basis of the thoracolumbar lateral radiographs of 95 acute OVFs in postmenopausal women (mean age 80.6 years; range: 64-103 years), supine and standing vertebral collapse rates (CRsp and CRst, respectively) were determined. Subsequently, VI was defined as follows: VI=CRst−CRsp. Using axial T2-weighted magnetic resonance imaging (MRI), CSA of the psoas major, erector spinae, and multifidus muscles at the L3/4 intervertebral disc level were measured. The BMD of the lumbar spine and proximal femur (total hip) was measured for all participants using dual-energy X-ray absorptiometry. The patients were classified into group 1 (VI <20%) and group 2 (VI ≥20%). RESULTS: We observed a negative correlation between VI and CSA of the erector spinae muscle (r=−0.3962, P<0.0001). No significant correlations were observed between VI and BMD. The CSA of the erector spinae muscle in group 2 was significantly lower than that in group 1 (P=0.0002). No significant difference in the BMD or the CSA of the psoas major or multifidus muscles was observed between the two groups. A multivariable analysis of factors of VI was performed. Both age (odds ratio [OR], 1.099; 95% confidence interval [CI], 1.015-1.189; P=0.020) and the CSA of the erector spinae (OR, 0.996; 95% CI, 0.993-0.999; P=0.020) were significant predictors of high VI. CONCLUSIONS: Although the severity of OVFs was related to the CSA of the erector spinae muscle, it was not associated with BMD.