Changes of the posterior paraspinal and psoas muscle in patients with low back pain: a 3-year longitudinal study

Purpose This study aimed to investigate the changes of the posterior paraspinal muscles (PPM) and psoas muscle in patients with low back pain (LBP) over time. Methods Patients with LBP who had a repeat lumbar MRI with a minimum of 3-years apart at a tertiary referral center were analyzed. MRI-based quantitative assessments of the PPM and the psoas muscle were conducted for the baseline and follow-up MRI. The cross sectional area (CSA), the functional cross sectional area (fCSA) and the fat area (FAT) were calculated using a dedicated software program. The fatty infiltration (FI,%) of the regions of interest was calculated. Differences between the 1st and 2nd MRI were calculated for all assessed muscular parameters. Results A total of 353 patients (54.4%female) with a median age of 60.1 years and BMI of 25.8 kg/m 2 at baseline were analyzed. The mean time between the 1st and 2nd MRI was 3.6 years. The fCSA PPM declined in both sexes significantly from the 1st to the 2nd MRI, whereas the FAT PPM increased. In line with this result, the FI PPM increased in both males (29.9%) and females (19.4%). Females had a higher FI PPM and FI Psoas than males in both MRIs. In females, no significant changes were found for the psoas muscle. The CSA Psoas and fCSA Psoas in males were significantly smaller in the 2nd MRI. With increasing age, a significant trend in a decrease in ∆FI PPM was observed for both sexes. Conclusion The study revealed significant quantitatively muscular changes in males and females, especially in the posterior paraspinal muscles in only three years’ time.