Paraspinal muscle quality in chronic low back pain: a systematic review and meta-analysis of muscle atrophy and fat infiltration

Background: Chronic low back pain (cLBP) is the leading cause of disability worldwide, yet the specific musculoskeletal mechanisms underlying symptom persistence remain poorly understood. Structural changes in the spine-supporting paraspinal muscles, particularly the multifidus, erector spinae, and psoas major, have been implicated in its pathophysiology, but current evidence remains inconclusive. Purpose: To summarise and quantify differences in lumbar paraspinal muscle morphology and composition—specifically total cross-sectional area (tCSA), functional cross-sectional area (fCSA), and fat infiltration (FI)—between individuals with cLBP and asymptomatic controls, with stratification by vertebral level to assess segmental specificity. Study design/setting: Systematic review and meta-analysis. Methods: A comprehensive literature search of electronic databases was conducted. Twenty-one studies were included in the qualitative synthesis, and 10 met criteria for meta-analysis. Standardised mean differences (SMDs) were calculated using random-effects models, and subgroup analyses were performed by vertebral level. Sensitivity analyses assessed the impact of study quality and methodological factors. Outcome measures: Imaging-derived assessments of paraspinal muscle tCSA, fCSA, and FI. Results: Individuals with cLBP exhibited significantly lower multifidus tCSA and fCSA, alongside higher FI, particularly at mid-to-lower lumbar levels (L3/L4 to L5), indicating segment-specific muscle atrophy. These findings were generally robust across sensitivity analyses, though some were influenced by demographic and methodological variability. In contrast, differences in erector spinae and psoas major were less consistent, often confined to isolated lumbar levels or revealed only after sensitivity testing. High between-study heterogeneity was attributed to differences in imaging modality, muscle segmentation techniques, and participant characteristics. Conclusions: Multifidus demonstrates the most consistent structural alterations among paraspinal muscles in individuals with cLBP, reinforcing its potential relevance in diagnosis and the development of targeted rehabilitation strategies. Future research should prioritise standardised imaging protocols and reporting practices to reduce heterogeneity and improve clinical translation.