Peripheral response to cervical or thoracic spinal manual therapy: an evidence-based review with meta analysis

Objectives: Spinal manual therapy (SMT) is commonly used for treatment of musculoskeletal pain in the neck, upper back, or upper extremity. Some authors report a multi-system effect of SMT, including peripheral alterations in skin conductance and skin temperature, suggesting that SMT may initiate a sympathetic nervous system (SNS) response. The focus of this evidence-based review and meta-analysis is to evaluate the evidence of SNS responses and clinically relevant outcomes following SMT to the cervical or thoracic spine. Methods: A systematic search used the terms: 'manual therapy', 'SMT', 'spinal manipulation', 'mobilization', 'SNS', 'autonomic nervous system', 'neurophysiology', 'hypoalgesia', 'pain pathophysiology', 'cervical vertebrae', 'thoracic vertebrae', 'upper extremity', and 'neurodynamic test'. Data were extracted and within-group and between-group effect sizes were calculated for outcomes of skin conductance, skin temperature, pain, and upper extremity range of motion (ROM) during upper limb neurodynamic tests (ULNTs). Results: Eleven studies were identified. Statistically significant changes were seen with increased skin conductance, decreased skin temperature, decreased pain, and increased upper extremity ROM during ULNT. Discussion: A mechanical stimulus at the cervical or thoracic spine can produce a SNS excitatory response (increased skin conductance and decreased skin temperature). Findings of reduced pain and increased ROM during ULNT provide support to the clinical relevance of SMT. This evidence points toward additional mechanisms underlying the therapeutic effect of SMT. The effect sizes are small to moderate and no long-term effects post-SMT were collected. Future research is needed to associate peripheral effects with a possible centrally-mediated response to SMT.