Background & Aims

Several cross-sectional studies investigated neural motor control in people with low back pain (LBP) and demonstrated altered cortical excitability and organization of trunk muscles[1,2] and that this organization is a predictor for persistence of pain 6 months later[3]. These differences in trunk neural motor networks have been proposed as the cause of altered trunk motor control observed in LBP. Although some prior systematic reviews have examined the state of cortical and spinal networks across various chronic pain conditions[4,5], none of these reviews provided an exhaustive overview of neural motor networks from multiple levels of the central nervous system and controlling a variety of muscles.
Thus, the aim of this study was to systematically review studies which investigated the functioning of neural motor control among people with LBP compared to pain-free people by use of a neurophysiological stimulation technique, and to conduct meta-analyses.

Methods

The four following databases CINHAL, Medline (OVID), Embase and Web of Science, were searched from their inception to March 23rd 2023, to identify all relevant studies that used neurophysiological stimulation technique to compare motor neural circuits organisation in participant with clinical or experimental LBP with pain-free controls. Data were grouped by neurophysiological outcomes (e.g. Transcranial Magnetic Stimulation (TMS) outcomes, vestibular reflex, H-reflex, stretch reflex…) and sub-grouped by type of pain (experimental/clinical) and by body localisation of the measurements. A meta-analysis was performed when two or more studies reported a similar outcome. Pooled standardised mean difference (SMD) with 95% confidence interval and heterogeneity (I²) were calculated for each meta-analysis.

Results

Twenty-six studies were included. Among them, fifteen studies were included in at least one meta-analysis. The meta-analyses included TMS outcomes measured on paraspinal and abdominal muscles, H-Reflex outcomes measured on the triceps sural muscles and stretch reflex outcomes assessed on paraspinal muscles. Map volume of paraspinal muscles appeared to be smaller in LBP (p=0.002, I2=0%, 5 studies, nLBP= 116, nCTL= 102, SMD = -0,43 [-0.70, -0.16]). The centre of gravity (CoG) coordinates of paraspinal muscles corticomotor representation was more medial in LBP (p<0.001, I2= 83%, 5 studies, nLBP= 116, nCTL= 102, SMD= -0,35 [-0.63, -0.08]), and the CoG of the transverse abdominal corticomotor representation was more posterior in LBP (p<0.0001, I2=60%, 2 studies, nLBP=35, nCTL =23, SMD= -1,62 [-2.26, -0.99]). Although the latter results were significant, high heterogeneity was present. No other significant effects were found.

Conclusions

These results indicate a reduced map volume in paraspinal muscles in participants with LBP, suggesting a decreased corticospinal excitability of the representation of low back muscles in the motor cortex. Additionally, the CoG coordinates of abdominal and paraspinal muscles were more posterior and more medial in participants with LBP suggesting, a different cortical organisation of trunk muscles. The high heterogeneity in some of these results could reflect the variety of methods used to measure these outcomes. Spinal excitability assessed by H-Reflex or stretch reflex did not show consistent differences in LBP. Subcortical networks such as the vestibulospinal or reticulospinal pathways which contribute to trunk motor control were poorly investigated.
Although cortical reorganisation in LBP seems plausible, larger studies using similar methodological approaches are critical to confirm and better establish potential alteration in neural motor networks in LBP.

References

1.Tsao, H., Danneels, L. A., & Hodges, P. W. (2011). ISSLS prize winner: smudging the motor brain in young adults with recurrent low back pain. Spine, 36(21), 1721-1727.
2.Schabrun, S. M., Elgueta-Cancino, E. L., & Hodges, P. W. (2017). Smudging of the motor cortex is related to the severity of low back pain. Spine, 42(15), 1172-1178
3.Jenkins, L. C., Chang, W. J., Buscemi, V., Liston, M., Skippen, P., Cashin, A. G., … & Schabrun, S. M. (2022). Low somatosensory cortex excitability in the acute stage of low back pain causes chronic pain. The Journal of Pain, 23(2), 289-304
4.Parker, R. S., Lewis, G. N., Rice, D. A., & McNair, P. J. (2016). Is motor cortical excitability altered in people with chronic pain? A systematic review and meta-analysis. Brain stimulation, 9(4), 488-500.
5.Sanderson, A., Wang, S. F., Elgueta?Cancino, E., Martinez?Valdes, E., Sanchis?Sanchez, E., Liew, B., & Falla, D. (2021). The effect of experimental and clinical musculoskeletal pain on spinal and supraspinal projections to motoneurons and motor unit properties in humans: A systematic review. European Journal of Pain, 25(8), 1668-1701.
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7.Costa, L. D. C. M., Maher, C. G., McAuley, J. H., Hancock, M. J., Herbert, R. D., Refshauge, K. M., & Henschke, N. (2009). Prognosis for patients with chronic low back pain: inception cohort study. Bmj, 339.
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Presenting Author

Amira Cherif

Poster Authors

Amira Cherif

PhD

Université Laval

Lead Author

Nadim Fakhry

Msc

Laval University, Cirris

Lead Author

Jeremy Pouliot

bachelor student

Laval University

Lead Author

Martin Simoneau

PhD

Laval Univerisity, Cirris

Lead Author

Hugo Massé-Alarie

PT

Laval University

Lead Author

Topics

  • Evidence, Clinical Trials, Systematic Review, Guidelines, and Implementation Science