Background: Current evidence suggests that spinal manipulative therapy (SMT) is effective in the treatment of people with low back pain (LBP); however, the corresponding mechanisms are unknown. Hypoalgesia is associated with SMT and is suggestive of specific mechanisms.
Objective: The primary purpose of this study was to assess the immediate effects of SMT on thermal pain perception in people with LBP. A secondary purpose was to determine whether the resulting hypoalgesia was a local effect and whether psychological influences were associated with changes in pain perception.
Design: This study was a randomized controlled trial.
Setting: A sample of convenience was recruited from community and outpatient clinics.
Participants: Thirty-six people (10 men, 26 women) currently experiencing LBP participated in the study. The average age of the participants was 32.39 (SD=12.63) years, and the average duration of LBP was 221.79 (SD=365.37) weeks.
Intervention and measurements: Baseline demographic and psychological measurements were obtained, followed by quantitative sensory testing to assess temporal summation and Adelta fiber-mediated pain perception. Next, participants were randomly assigned to ride a stationary bicycle, perform low back extension exercises, or receive SMT. Finally, the same quantitative sensory testing protocol was reassessed to determine the immediate effects of each intervention on thermal pain sensitivity.
Results: Hypoalgesia to Adelta fiber-mediated pain perception was not observed. Group-dependent hypoalgesia of temporal summation specific to the lumbar innervated region was observed. Pair-wise comparisons indicated significant hypoalgesia in participants who received SMT, but not in those who rode a stationary bicycle or performed low back extension exercises. Psychological factors did not significantly correlate with changes in temporal summation in participants who received SMT.
Limitations: Only immediate effects of SMT were measured, so the authors are unable to comment on whether the inhibition of temporal summation is a lasting effect. Furthermore, the authors are unable to comment on the relationship between their findings and changes in clinical pain.
Conclusions: Inhibition of Adelta fiber-mediated pain perception was similar for all groups. However, inhibition of temporal summation was observed only in participants receiving SMT, suggesting a modulation of dorsal horn excitability that was observed primarily in the lumbar innervated area.
Trial registration: ClinicalTrials.gov NCT00922220.