202. Association of MRI-based spinal muscle parameters and vertebral bone quality score in lumbar fusion patients

Abstract

<h3>BACKGROUND CONTEXT</h3> Pathophysiological conditions during aging can affect bone and muscle simultaneously, such as in osteosarcopenia. The vertebral bone quality (VBQ) score based on magnetic resonance imaging (MRI) was recently introduced as a novel measure of bone quality in the lumbar spine and shown to be a significant predictor of healthy versus osteopenic/osteoporotic bone. However, the association between quantitative lumbar spinal muscle parameters and the VBQ score, is unknown. <h3>PURPOSE</h3> This study aimed to assess possible associations between the functional cross-sectional area (FCSA) of psoas and lumbar spine extensor muscles (multifidus and erector spinae) and the VBQ score. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study. <h3>PATIENT SAMPLE</h3> Patients who underwent open posterior lumbar fusion for degenerative conditions between 2014 and 2017 at a single academic institution and had both a lumbar MRI and a computed tomography (CT) scan within 6 months prior to surgery were included. <h3>OUTCOME MEASURES</h3> FCSA and VBQ score. <h3>METHODS</h3> MRI measurements included psoas and combined multifidus and erector spinae (paraspinal) FCSA at the L3-L5 superior endplate. Following manual segmentation of muscles on axial T2-weighted images using ITK-SNAP (version 3.8), the FCSA was calculated using a custom written program on Matlab (version R2019a, The MathWorks, Inc.) that used an automated pixel intensity threshold method to differentiate between fat (high intensity) and muscle (low intensity). VBQ measurements included the signal intensity of the medullary portion of the vertebrae L1-L4 and the cerebrospinal fluid (CSF) at L3 on mid-sagittal T1-weighted MR images. The VBQ score was calculated by dividing the median signal intensity L1-L4 through the signal intensity of the CSF. Lumbar volumetric bone mineral density (vBMD) was assessed by quantitative CT using the L1/2 average, categorizing patients with a vBMD of <120 mg/cm³ as osteopenic/osteoporotic. All analyses were stratified by biological sex. Sperman correlation and multivariate linear regression analysis with adjustments for age and body mass index (BMI) were performed. <h3>RESULTS</h3> Eighty patients (58.8% female) were included in the analysis. The patient population was 93.8% Caucasian with a median age at surgery of 68.8 years. The prevalence of chronic low back pain >12 weeks was 83.8%, and the prevalence of osteopenia/osteoporosis was 65%, with no significant differences between men and women. All muscle measurements were significantly greater in men. The mean (SD) VBQ score was significantly smaller in men, at 2.26 (0.45) versus women at 2.59 (0.39) (p = 0.001). In men, a significant negative correlation was seen between psoas FCSA at L3-5 and the VBQ score, with correlation coefficients ranging from -0.487 to -0.405. After adjusting for age and BMI, a significant negative association was seen between psoas FCSA at L3 and the VBQ score in men (β = -0.373; 95% CI -0.687 - -0.058; p = 0.022). In women, there was a significant negative correlation between paraspinal FCSA at L3 and the VBQ score, with a correlation coefficient of -0.367 (p = 0.011), but no significant association was seen in the adjusted analysis. <h3>CONCLUSIONS</h3> We found the VBQ score to be negatively associated with psoas FCSA at L3 among male individuals, irrespective of age and BMI. Our results highlight sex differences in the VBQ score that were not demonstrated by vBMD or categorial bone status, and suggest a potential role of this novel measure to assess not only bone quality, but also spinal muscle quantity. Further studies are needed to assess the clinical utility of the VBQ score as a non-invasive screening tool for osteosarcopenia. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.