Psoas Major Volume Asymmetry, Not Attachment Site Asymmetry, is Associated with Chronic Low Back Pain Status

Abstract Purpose To determine whether psoas major muscle (PMM) volume and attachment-site asymmetry are associated with chronic low back pain (CLBP). Exploratory analyses examined associations between PMM volume asymmetry and disability, physical activity, and age. Methods This retrospective secondary analysis included adults aged 35–65 years with and without CLBP from the NIH-sponsored BACPAC imaging cohort. Participants were propensity score matched on age, BMI, and sex. Automated segmentation (MuscleMap) was used to quantify bilateral PMM volumes, and volume asymmetry was calculated as the percent difference between left and right volumes. Attachment-site asymmetry was assessed using axial and coronal MRI classifications. Binary logistic regression evaluated associations between PMM volume and attachment-site asymmetry and CLBP status. Exploratory multiple linear regression evaluated associations between PMM volume asymmetry and disability, physical activity, age, and CLBP status. Results Greater PMM volume asymmetry was associated with higher odds of CLBP (OR = 1.08 per 1% increase, 95% CI 1.02–1.14, p = .007). Neither axial nor coronal attachment-site asymmetry was significantly associated with CLBP. The exploratory model was not statistically significant ( F (4,172) = 2.01, p = .095), and disability, physical activity, age, and CLBP status were not individually significantly associated with PMM volume asymmetry. Conclusion Greater PMM volume asymmetry was associated with CLBP, whereas attachment-site asymmetry was not. These findings support further investigation of PMM volume asymmetry as a morphological feature associated with CLBP.