Evaluation of Paraspinal Muscle Epimuscular Fat in Subjects With Low Back Pain in a Tertiary Care Setting

Low back pain (LBP) is among the most commonly encountered health complaints globally, significantly affecting the person's quality of life and imposing a substantial financial burden on individuals and society. Structural alterations in paraspinal muscles, particularly fatty infiltration, have been associated with chronic LBP. However, limited studies have specifically focused on the role of epimuscular fat (EF) in LBP, and it remains less understood.

This study aimed to evaluate the distribution of paraspinal muscle EF in patients with chronic nonspecific LBP and to investigate its associations with demographic parameters, body mass index (BMI), and the severity of LBP.

A cross-sectional study was conducted involving 56 participants presenting with chronic nonspecific LBP at RL Jalappa Hospital and Research Centre, a rural tertiary care hospital attached to Sri Devaraj Urs Medical College in Tamaka, Kolar, Karnataka, India. EF was graded on a 0-5 qualitative scale for multifidus (MF) and erector spinae (ES) paraspinal muscles at lumbar intervertebral disc levels on T2 axial magnetic resonance imaging (MRI) sequences acquired using Siemens® MAGNETOM Avanto (Siemens Healthineers, Erlangen, Germany), a Tim+Dot 1.5 Tesla, 18-channel MRI machine. The Oswestry Disability Index (ODI) questionnaire was used for LBP severity assessment. Demographic data, including age, sex, and BMI, were recorded. Spearman's correlation and comparative analyses using independent t-tests, multiple group comparison tests, and multiple linear regression were performed to evaluate associations between EF and clinical-demographic variables.

Fifty-six participants (mean age 45.3±12.7 years; BMI 27.4±4.5 kg/m²; 46.4% female) were included. EF scores increased from L1-L2 (2.1±0.8) to L4-L5 (7.2±1.4) and L5-S1 (6.8±1.2). EF showed significant positive correlations with age (r=0.45) and BMI (r=0.52) (both p<0.001). Women had higher EF scores than men (p=0.017). EF also increased across BMI categories (p=0.033) and ODI-based LBP severity levels (p=0.0036). Regression analysis identified age, BMI, sex, and ODI severity as independent EF predictors (R²=0.44; adjusted R²=0.41).

EF accumulation correlates significantly with age, BMI, sex, and chronic LBP severity, with a predilection for lower lumbar levels suggestive of biomechanical adaptation. These findings highlight EF as a potential biomarker and therapeutic target. Interventions aimed at EF reduction may enhance spinal stability and alleviate symptoms. Further longitudinal studies are warranted to validate these associations.