Psoas major and lumbar lordosis may correlate with pain episodes during Sorensen test in patients with non-specific low back pain

BACKGROUND: The reason that participants develop pain episodes during the Sorensen test remains unclear. Lumbar lordosis and trunk muscle are important for dynamic stability of the spine; however, their role in pain episodes during the Sorensen test has not yet been discussed. OBJECTIVE: To investigate the effects of muscular morphology and lumbar curvature on pain development during the Sorensen test in patients with non-specific low back pain (LBP). METHODS: Ninety-one patients diagnosed with chronic non-specific LBP and underwent the Sorensen test were enrolled. Lumbar lordosis, cross-sectional area and fat infiltration rate of trunk muscle and centroid line of psoas major (dividing into three types: anterior arc, linear and posterior arc) were measured using ImageJ software. All recruited patients were grouped into pain episode and exhaustion groups and were matched for the confounders based on propensity scores. The above parameters were compared between groups and further adjusted for confounding bias. RESULTS: After adjustment, the mean differences in lumbar lordosis of 12.1 +/- 2.3 degrees between the two groups in the complete cohort and of 13.9 +/- 2.5 degrees in the matching cohort remained significant, the exhaustion group had a 0.22-fold and 0.08-fold risk of presenting as linear and posterior arc types, respectively, compared with the pain episode group in the complete cohort (p = 0.008, p = 0.004), the corresponding values were 0.19-fold and 0.05-fold, respectively, in the matching cohort ( p = 0.014, p = 0.010). Logistic regression demonstrated that lumbar lordosis, the linear and posterior arc types were significantly associated with pain episode during the test (OR = 0.78, p < 0.001; OR = 4.50, p = 0.038; OR = 9.93, p = 0.033). CONCLUSIONS: Lower lumbar lordosis and linear and posterior arc types of the psoas major centroid line were possibly relevant to the pain episode during Sorensen test in patients with chronic non-specific LBP.