The state of motor neural networks in low back pain: a systematic review and meta-analysis

Low back pain (LBP) is one of the most prevalent musculoskeletal disorders and often shows poor recovery. Although symptom persistence is multifactorial, trunk motor control changes are frequently observed and suggested to result from reorganisation of motor neural networks. Understanding these mechanisms may help guide more effective interventions. This systematic review with meta-analysis (PROSPERO: CRD42023417238) aims to compare motor neural network state between individuals with LBP and pain-free controls, and under experimental LBP conditions. Four databases (CINAHL, Medline, Embase, Web of Science) were searched. Data were pooled according to outcomes, experimental/clinical pain, and muscle groups. Thirty-three studies were included, and 20 meta-analyses conducted. For paraspinal muscles, limited evidence of smaller map area (n_LBP=58, n_controls=45, SMD=-0.44 [-0.84, -0.04]) and volume (n_LBP=136, n_controls=121, SMD=-0.46 [-0.71, -0.21]), and moderate evidence of lower motor evoked potential amplitude (n_LBP=84, n_controls=60, SMD=-0.57 [-0.91, -0.22]) were found in LBP participants. For abdominal muscles, limited evidence of greater map area (n_LBP=49, n_controls=37, SMD=0.53 [0.09, 0.97]) and very limited evidence of a more posterior cortical location (n_LBP=60, n_controls=48, SMD=-1.22 [-2.37, -0.07]) were observed. However, map area findings were not supported by sensitivity analyses. Limited evidence of higher resting motor threshold was also observed in finger muscles (n_LBP = 78, n_controls = 76, SMD = 0.67 [0.35, 1.00]). These findings suggest (i) corticomotor adaptations of trunk muscles in opposite directions depending on muscle groups tested, and (ii) neuroplasticity generalised to hand motor neural networks. The certainty of evidence and heterogeneity in outcome measures limit further conclusions. PERSPECTIVE: This study offers valuable insights into the organisation and excitability of motor networks in LBP. Such knowledge could help refine hypotheses about how chronic pain influences motor adaptation to pain, improve methodological consistency between studies, and guide future research towards the development of more tailored interventions for patients with LBP.