Exploring the immediate and short-term effect of lumbar spinal manipulation on pressure pain threshold: a randomized controlled trial of healthy participants

Background Lumbar spinal manipulative therapy (SMT) is a common intervention used to treat low back pain (LBP); however, the exact neurophysiological mechanisms of SMT reducing pain measured through pain pressure threshold (PPT) have not been fully explored beyond an immediate timeframe (e.g., immediately or five-minutes following) referencing a control group. Therefore, the purpose of this study was to investigate the neurophysiological effects of lumbar SMT compared to deactivated ultrasound using PPT immediately following and 30-minutes following SMT. Methods A longitudinal, randomized controlled trial design was conducted between September to October 2023. Fifty-five participants were randomized into a control group of deactivated ultrasound (n = 29) or treatment group of right sidelying lumbar SMT (n = 26). PPT, recorded at the right posterior superior iliac spine (PSIS), was documented for each participant in each group prior to intervention, immediately, and 30-minutes after. A repeated measures ANOVA, with a post-hoc Bonferroni adjustment, was used to assess within-group and between-group differences in PPT. The significance level was set at a < 0.05 a priori. Results Statistically significant differences were found between the deactivated ultrasound and lumbar SMT groups immediately (p = .05) and 30-minutes (p = .02) following intervention. A significant difference in the lumbar SMT group was identified from baseline to immediately following (p < .001) and 30-minutes following (p < .001), but no differences between immediately following and 30-minutes following intervention (p = .10). The deactivated ultrasound group demonstrated a difference between baseline and immediately after intervention with a reduced PPT (p = .003), but no significant difference was found from baseline to 30-minutes (p = .11) or immediately after intervention to 30-minutes (p = 1.0). Conclusion A right sidelying lumbar manipulation increased PPT at the right PSIS immediately after that lasted to 30-minutes when compared to a deactivated ultrasound control group. Future studies should further explore beyond the immediate and short-term neurophysiological effects of lumbar SMT to validate these findings.