Quantitative MRI for structural changes in lumbar paraspinal muscles in patients with chronic non-specific low back pain

Objective To quantitatively assess the structural changes of the lumbar paraspinal muscles in patients with chronic non-specific low back pain (CNLBP) using conventional magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) in order to provide a reference for the clinical diagnosis and treatment of CNLBP. Methods A total of 45 CNLBP patients admitted to our hospital from April 2022 to March 2023 were enrolled and assigned into CNLBP group, and another 28 healthy volunteers were recruited and assigned into control group. Sagittal and axial T2WI and DTI MRI scans were performed to all the subjects at the same time. The axial T2WI and DTI images at the L3/4, L4/5 and L5/S1 intervertebral disc levels were used to measure the functional cross-sectional area (FCSA), fat infiltration rate (FIR), fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of the bilateral multifidus and erector spinae muscle. Visual analog scale (VAS) and Oswestry disability index (ODI) were employed to assess the severity of pain and functional impairment in the patients. The general data (age, sex, height, body weight and BMI), and the relative functional cross-sectional area (RFCSA), FIR, FA and ADC values of bilateral multifidus and erector spinae muscles were compared between the CNBLP group and the control group. Multiple linear regression was applied to analyze the correlations of age, gender, BMI and lower back pain with the FIR value of bilateral multifidus and erector spinae muscle. Spearman analysis was performed to determine the correlations of VAS and ODI scores with RFCSA, FIR, FA and ADC values of the muscles. Results There were no statistical differences in the general data between the CNLBP and control groups. The RFCSA values of the bilateral multifidus and erector spinae muscles were decreased in the former group than the latter group, though no significant difference. The CNLBP group had obviously higher FIR values of the 2 muscles than the control group (P < 0.05). Multiple linear regression analysis showed that age was positively associated with FIR, BMI was not, and the females and the patients with LBP were more likely to develop fatty infiltration. Spearman analysis indicated that the ODI score was negatively correlated with the RFCSA values of the 2 muscles (P < 0.05), and both VAS and ODI scores were positively correlated with the FIR values of the 2 muscles (P < 0.05). A decrease in the FA value and an increase in the ADC value of the 2 muscles were found in the CNLBP group. And the differences in FA of the right multifidus muscle at the L3/4 segment and FA and ADC values of the bilateral multifidus muscle at the L4/5 and L5/S1 segments, and FA values at the L4/5 and L5/S1 segments and ADC values at the L5/S1 segment of the bilateral erector spinae muscle were statistically significant (P < 0.05). Conclusion CNLBP patients are accompanied by muscle atrophy, fat infiltration and changes in muscle fiber structure. Multimodal MRI technology can observe and quantitatively assess these changes in the muscle structure.