Quantitative MRI assessment of paraspinal muscles and the psoas: associations with low back pain

Background: Low back pain (LBP) is a leading cause of disability worldwide, yet the contribution of paraspinal muscle fat infiltration remains uncertain. This study aimed to quantitatively assess paraspinal muscle fat fraction using the Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation for Imaging Quantification (IDEAL-IQ) sequence in patients with LBP and to explore its relationships with pain severity, disability, and demographic factors such as age, sex, and body mass index (BMI). Methods: This retrospective cross-sectional study included 124 patients (64 males, 60 females; mean age, 38.3±12.6 years). Fat fraction values of the multifidus, erector spinae, and psoas muscles were measured bilaterally at L1-L2 through L4-L5 levels using IDEAL-IQ. Pain and disability were assessed with the Visual Analog Scale (VAS) and Oswestry Disability Index (ODI). Correlation and multiple regression analyses were conducted to determine associations, adjusting for age, sex, and BMI. Interobserver agreement between two radiologists was evaluated using the intraclass correlation coefficient (ICC). Results: 4.1-5.0% in males). These differences were statistically significant for all lumbar levels except psoas at L2-L3 and L4-L5. BMI showed a positive correlation with fat fraction across all lumbar levels (r=0.29-0.50, all P