Exploring the bidirectional effects of visceral and cervical manual therapies on viscero-sympathetic interactions in non-specific neck pain: A systematic review

Background: Non-specific neck pain (NSNP) is a highly prevalent condition with a multifactorial etiology, involving musculoskeletal, psychosocial, and potentially visceral-autonomic contributors. Although somatic and psychosocial mechanisms are widely discussed, the possible role of visceral dysfunction and autonomic regulation in NSNP has not been systematically examined. According to the viscero-sympathetic model, persistent visceral dysfunctions may influence somatic pain processing and contribute to chronic pain syndromes. Objective: To investigate whether dysfunctions of subdiaphragmatic, intrathoracic, or pelvic organs are associated with cervical pain or dysfunction; manual therapy (MT) directed at visceral regions improves cervical symptoms; and cervical spine MT influences visceral or autonomic function. Methods: A systematic review was conducted according to PRISMA 2020 guidelines and registered in PROSPERO. Eligibility criteria were defined using the Population, Exposure, Comparison, Outcome model for the first research question and the Population, Intervention, Comparison, Outcome model for the second and third. Fourteen studies involving 642 participants were included. Risk of bias was assessed using the Revised Cochrane Risk of Bias tool 2 and the Risk Of Bias In Nonrandomized Studies of Exposures. Results: One low-quality cross-sectional study addressed the association between visceral dysfunction and cervical symptoms, reporting a possible relationship between gastritis and cervical dysfunctions. However, interpretation was limited by small sample size, high risk of bias, and inability to infer causality. Four studies investigated visceral-region MT; three reported reductions in neck pain after subdiaphragmatic MT, while one high-quality study reported improved cervical mobility. Nevertheless, evidence was limited by heterogeneity and small samples sizes. Nine studies examined the effects of cervical MT on autonomic or visceral-related outcomes, including cortisol, cardiovascular parameters, and heart rate variability, with conflicting findings and generally low-quality evidence. Conclusions: The relationship between visceral dysfunction, autonomic regulation, and NSNP remains uncertain. Further high-quality trials are needed to clarify these associations and their clinical relevance