Abstract

Chronic low back pain (CLBP) is a leading cause of disability worldwide, with increasing evidence implicating neuromuscular factors such as muscle asymmetry in its pathophysiology. The psoas major muscle (PMM), a key contributor to lumbar spine stability, has been comparatively under-investigated despite its biomechanical importance. PURPOSE: To determine whether right-to-left differences in PMM volume and attachment site asymmetry are associated with CLBP; to evaluate whether ODI, IPAQ, and age are associated with PMM volume imbalance; and to assess whether combined PMM volume and attachment asymmetry are associated with CLBP. METHODS: A retrospective secondary analysis was conducted using lumbar MRI data from the NIH-sponsored BACPAC cohort. Adults aged 35-65 years with and without CLBP were propensity score matched on age, BMI, and sex. PMM volumes were quantified using automated segmentation (MuscleMap), and asymmetry was calculated as the percent difference between sides. Attachment site asymmetry was assessed using axial and coronal MRI classifications. RESULTS: Logistic regression analyses demonstrated that greater PMM volume asymmetry was significantly associated with higher odds of CLBP (OR = 1.08 per 1% increase, 95% CI [1.02, 1.14], p = .007). In contrast, disability (ODI), physical activity (IPAQ), and age were not significant predictors of PMM asymmetry. Furthermore, in mixed-effects models, PMM volume asymmetry remained a significant predictor of CLBP (p = .002), whereas neither axial nor coronal attachment site asymmetry showed significant associations. CONCLUSIONS: These findings suggest that bilateral imbalance in PMM volume, rather than anatomical attachment variation, may play a more critical role in CLBP. This study also demonstrates the feasibility of using open-source automated segmentation tools to efficiently analyze large imaging datasets. Overall, PMM volume asymmetry may represent a clinically relevant imaging biomarker and potential target for rehabilitation, supporting a shift toward more targeted and mechanism-based approaches in the management of chronic low back pain.

Degree

MS

College and Department

Life Sciences; Exercise Sciences

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2026-04-17

Document Type

Thesis

Keywords

chronic low back pain, psoas major muscle, muscle asymmetry, magnetic resonance imaging, muscle volume, automated segmentation

Language

english

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