Background and objectives

Nervous system, psychosocial and spinal tissue biomarkers are associated with non-specific low back pain (nsLBP), though relative contributions are unclear.

Databases and data treatment

MEDLINE, EMBASE, CINAHL, PsycINFO and SPORTDiscus were searched up to 25 March 2020. Related reviews and reference lists were also screened. Observational studies examining structural and functional nervous system biomarkers (e.g. quantitative sensory tests, structural and functional brain measures), psychosocial factors (e.g. mental health, catastrophizing) and structural spinal imaging biomarkers (e.g. intervertebral disc degeneration, paraspinal muscle size) between nsLBP and pain-free controls were included. For multivariate meta-analysis, two of three domains were required in each study. Random-effects pairwise and multivariate meta-analyses were performed. GRADE approach assessed evidence certainty. Newcastle-Ottawa scale assessed risk of bias. Main outcomes were effect size difference of domains between nsLBP and pain-free controls.

Results

Of 4519 unique records identified, 33 studies (LBP=1552, referents=1322) were meta-analysed. Psychosocial state (Hedges’ g [95%CI]: 0.90 [0.69-1.10], p<0.001) in nsLBP showed larger effect sizes than nervous system (0.31 [0.13-0.49], p<0.001; difference: 0.61 [0.36-0.86], p<0.001) and spine imaging biomarkers (0.55 [0.37-0.73], p<0.001; difference: 0.36 [0.04-0.67], p=0.027). The relationship between domains changes depending on if pain duration is acute or chronic.

Conclusions

Psychosocial effect sizes in nsLBP are greater than that for spinal imaging and nervous system biomarkers. Limitations include cross-sectional design of studies included and inference of causality. Future research should investigate the clinical relevance of these effect size differences in relation to pain intensity and disability.