Spinal manipulative therapy-specific changes in pain sensitivity in individuals with low back pain (NCT01168999)

Abstract

Spinal manipulative therapy (SMT) is effective for some individuals experiencing low back pain; however, the mechanisms are not established regarding the role of placebo. SMT is associated with changes in pain sensitivity, suggesting related altered central nervous system response or processing of afferent nociceptive input. Placebo is also associated with changes in pain sensitivity, and the efficacy of SMT for changes in pain sensitivity beyond placebo has not been adequately considered. We randomly assigned 110 participants with low back pain to receive SMT, placebo SMT, placebo SMT with the instructional set "The manual therapy technique you will receive has been shown to significantly reduce low back pain in some people," or no intervention. Participants receiving the SMT and placebo SMT received their assigned intervention 6 times over 2 weeks. Pain sensitivity was assessed prior to and immediately following the assigned intervention during the first session. Clinical outcomes were assessed at baseline and following 2 weeks of participation in the study. Immediate attenuation of suprathreshold heat response was greatest following SMT (P = .05, partial η(2) = .07). Group-dependent differences were not observed for changes in pain intensity and disability at 2 weeks. Participant satisfaction was greatest following the enhanced placebo SMT. This study was registered at www.clinicaltrials.gov under the identifier NCT01168999.

Perspective: The results of this study indicate attenuation of pain sensitivity is greater in response to SMT than the expectation of receiving an SMT. These findings suggest a potential mechanism of SMT related to lessening of central sensitization and may indicate a preclinical effect beyond the expectations of receiving SMT.

Keywords: Central sensitization; low back pain; manual therapy; placebo; spinal manipulation.

Figure 1

Summary of recruitment, enrollment, randomization, follow up, and analysis for study

Figure 2. Illustration of the spinal manipulative therapy (SMT) and the placebo SMT

The SMT (A) is effective in the treatment of some individuals experiencing low back pain and has been previously demonstrated to attenuate suprathreshold heat response. The participant was positioned supine in lumbar sidebending and contralateral lumbar rotation for the lumbar SMT. A high velocity, low amplitude force was then applied through the pelvis to further rotate the lumbar spine. The participant was positioned with a neutral spine (i.e. without apparent sidebending or rotation) for the placebo SMT. The participant was log rolled into sidelying and then returned to supine. A thrust of similar magnitude of force as was applied during the SMT was then applied to the pelvis which remained in contact with the table to prevent motion. Arrows indicate direction of the force.

Figure 3. Immediate Within Session Changes in Suprathreshold Heat Response

Immediate (pre- intervention to immediately post intervention) within session changes in suprathreshold heat response. Bars represent change scores (pre to post intervention) with positive numbers on the y-axis indicating a lessening of pain sensitivity in response to an intervention. A significant group × time interaction was observed (p=0.05) indicating group dependent changes in suprathreshold heat response. * = significant lessening of pain sensitivity (p= 0.05). Error bars= standard error of the mean. SMT= spinal manipulative therapy.

Figure 4. Two Week Changes in Clinical Outcomes

Two week changes in low back related pain intensity and disability. Pain intensity was measured with a 101 point numeric rating scale anchored with 0= no pain to 100= worst pain imaginable for the “usual” pain over the past week. Disability was assessed with the Oswestry Disability Index. Bars represent change scores (baseline to 2 weeks) with positive numbers on the y- axis indicating reductions in pain and disability in response to an intervention. A significant main effect for time was observed for both pain and disability; however, neither was dependent upon group assignment. Error bars= standard error of the mean. SMT= spinal manipulative therapy.