No Sufficient Evidence for an Immediate Hypoalgesic Effect of Spinal Manual Therapy on Pressure Pain Thresholds in Asymptomatic and Chronic Pain Populations: A Systematic Review and Meta-Analysis

Objective Spinal manual therapy (SMT) is often used to treat patients with spinal disorders; however, the underlying mechanisms of SMT are not fully understood. This systematic review and meta-analysis investigates the effect of SMT compared with sham treatment or no intervention on local or remote (segmental or non-segmental) pressure pain thresholds (PPTs) in patients with chronic musculoskeletal conditions and people who are pain free. Methods A systematic search was conducted in the PubMed, Cochrane Library, Web of Science, and CINAHL databases. Randomized controlled trials investigating the effect of SMT on PPTs in patients with chronic musculoskeletal conditions and in people who were pain free were included. Quality assessment and evidence synthesis were performed according to Cochrane Handbook recommendations. A meta-analysis was performed using standardized mean difference and 95% CIs. Results Twenty-two reports were included in the present review. There were no significant results for an immediate effect of SMT on local (low certainty of evidence), remote (segmental) (low certainty of evidence), and remote (non-segmental) (low certainty of evidence) PPTs in patients with chronic pain as well as on local (moderate certainty of evidence) and remote (segmental) (low certainty of evidence) PPTs in people who were pain free. A small but significant effect (standardized mean difference = 0.26; 95% CI = 0.01 to 0.51; low certainty of evidence) was observed on remote (non-segmental) PPTs in people who were pain free, which was not considered a meaningful effect size. Conclusion No immediate, consistent, or meaningful hypoalgetic effect of SMT was shown on PPTs on various body areas. Involvement of spinal or supraspinal underlying mechanisms were, therefore, not confirmed via PPTs but should still be investigated using methods designed to assess central nervous pain processing. Impact No consistent and meaningful hypoalgesic effects of spinal manual therapy were demonstrated on PPTs in participants who were pain free and in patients with chronic musculoskeletal disorders.