Chiropractors believe that their spinal manipulations bring about a reduction in pain perception, and they often call this ‘manipulation-induced hypoalgesia’ (MIH). It is unknown, however, whether MIH following high-velocity low-amplitude spinal manipulative therapy is a specific and clinically relevant treatment effect.
This systematic review was an effort in finding out.
The authors investigated changes in quantitative sensory testing measures following high-velocity low-amplitude spinal manipulative therapy in musculoskeletal pain populations, in randomised controlled trials. Their objectives were to compare changes in quantitative sensory testing outcomes after spinal manipulative therapy vs. sham, control and active interventions, to estimate the magnitude of change over time, and to determine whether changes are systemic or not.
Fifteen studies were included. Thirteen measured pressure pain threshold, and 4 of these were sham-controlled. Change in pressure pain threshold after spinal manipulative therapy compared to sham revealed no significant difference. Pressure pain threshold increased significantly over time after spinal manipulative therapy (0.32 kg/cm2, CI 0.22–0.42), which occurred systemically. There were too few studies comparing to other interventions or for other types of quantitative sensory testing to make robust conclusions about these.
The authors concluded that they found that systemic MIH (for pressure pain threshold) does occur in musculoskeletal pain populations, though there was low quality evidence of no significant difference compared to sham manipulation. Future research should focus on the clinical relevance of MIH, and different types of quantitative sensory tests.
An odd conclusion, if there ever was one!
A more straight forward conclusion might be this:
MIH is yet another myth to add to the long list of bogus claims made by chiropractors.
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“Significant changes in PPT over time were not isolated to any one category of chronicity, and occurred in neck pain and extremity pain populations but inconsistently in low back pain populations. Studies investigating cervical SMT consistently demonstrated a significant increase in PPT over time, which was inconsistent after thoracic SMT and did not occur after lumbar SMT (regardless of musculoskeletal pain site).”