The relationship between pain and functional disability with morphological changes of psoas major in discogenic low back pain patients

Background/Aims: The psoas major muscle acts not only as a spine flexor, but also as a spine stabiliser. This study was conducted to investigate correlations between pain level and functional disability with morphological changes of the psoas major muscle in chronic low back pain patients with disc herniation. Method: Chronic low back pain patients with disc herniation were examined with routine lumbar MRI. An observational study was carried out using a convenience sample of 30 patients (mean age of 43.6 ± 6.8 years) of chronic low back pain with lumbar posterolateral disc herniation at L4–L5. Outcome measures included pain level, functional disability (ODI score), cross-sectional area, and fatty infiltration of psoas major muscle ipsilateral to the side of disc herniation. Results: There were significant correlations between functional disability with the cross-sectional areas and fatty infiltration of the psoas major muscle (r=-0.42, P=0.02) and (r=0.55, P=0.002) respectively. There was a significant correlation between pain level and fatty infiltration but not in the cross-sectional area of the psoas major muscle (r=0.44, P=0.015) and (r=-0.288, P=0.123) respectively. Linear regression analysis indicated that increasing the fatty infiltration grade by one unit leads to increasing functional disabilities and pain score by 7.3 and 0.8, respectively. Conclusions: Functional disability was correlated with the cross-sectional areas and fatty infiltration of the psoas major muscle, however pain showed a positive relationship with fatty infiltration only. The fatty infiltration of the psoas major muscle might be used as a good predictor for functional performance and pain level in chronic low back pain patients with disc herniation.