Abstract

Chronic low back pain (CLBP) is the leading cause of years lived with disability worldwide, negatively affecting individual’s quality of life. CLBP is associated with weakened paraspinal muscles, specifically, those involved with extension; multifidus (MF) and erector spinae (ES). The relationships between muscle size (e.g., cross-sectional area [CSA] and volume), intramuscular fat (IMF) and strength of the paraspinal muscles are not clear in those with and without CLBP. Few imaging studies have looked at the relationship between paraspinal muscles morphology and strength, but most had important methodological limitations including i) measurements were only acquired in healthy individuals, ii) not all paraspinal muscle and/or spinal level were investigated, and iii) sub-optimal imaging protocols were used.
This exploratory study investigated the relationship between paraspinal muscle size (e.g., CSA and volume), quality (e.g., IMF), and lumbar extensor muscle strength at each spinal level in subjects with and without CLBP. A total of 44 participants (n= 22 with CLBP and n= 22 healthy participants) were included. Lumbar extensor strength was assessed using the MedX lumbar extension machine, and MRI scans were acquired using IDEAL fat-water sequences to quantify CSA, volume, and IMF of the MF, ES, psoas (PS) and quadratus lumborum (QL) bilaterally, at upper (e.g., L1-L3) and lower (e.g., L4-S1) lumbar level. Automatic segmentation of the paraspinal muscles were performed using computer vision models, and a tiling approach was applied to assess the spatial distribution of IMF across medial-to-lateral and superficial-to-deep regions.
The Shapiro-Wilk test was used to assess normality of mean CSA, mean volume, mean IMF, and mean isokinetic strength for all four paraspinal muscles at the five lumbar levels. Multiple linear regression models were conducted to examine associations between paraspinal muscle morphology and mean lumbar extension torque at upper (e.g., L1-L3) and lower (e.g., L4-S1) lumbar levels, while adjusting for age, sex, and BMI. These findings highlight potential associations between paraspinal muscle morphology and lumbar strength in individuals with LBP and may help inform rehabilitation guidelines and treatment strategies to improve LBP prognosis.