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

PainSci » bibliography » Bialosky et al 2014
Tags: spinal adjustment, back pain, mind, spine, treatment, pain problems

PainSci commentary on Bialosky 2014: ?This page is one of thousands in the bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.

This intriguing 2014 experiment compared several effects of spinal manipulative therapy (SMT, or spinal "adjustment") on 110 people with back pain and had some odd features. Most notably, the researchers compared vanilla SMT to both a placebo and to an "enhanced" placebo. That is, one group just got fake SMT, and another got fake SMT but they were told that their treatment "has been shown to significantly reduce low back pain in some people."

In addition to the usual outcomes (pain, disability), they also measured sensitivity right after treatment. That is, the measured the immediate effect on sensitivity to noxious stimuli in the spine in addition to what the usual target: an improvement in symptoms, the clinical impact of the treatment.

What was the sham manipulation? A fairly clever imitation of real SMT, with similar contortions and movements, and applying some force to the spine — and yet “vastly differently from typical clinical practice.”

All of this is quite an unusual study design, and a good one. It’s a thoughtful and creative approach to some interesting questions. However, in my opinion, it had only one important result:

We did not observe group related differences in clinical pain or disability over the two weeks of the study despite differences in blinding, expectation, and immediate within session changes in pain sensitivity.”

In other words, SMT did not help people with back pain … not even when patients were told that it would. They couldn’t even get a lousy placebo effect!

I think the authors grasp at straws to come to a positive conclusion despite the data. They did observe a drop in sensitivity after receiving SMT, compared to the other test groups, and that sounds good. However, the effect was minor and affected only one of four measures of sensitivity — and heat sensitivity, not mechanical sensitivity — and it wouldn't be persuasive or important on its own in any case.

Nevertheless, the authors conclude: “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.”

Yes, and maybe I will fart a rainbow tomorrow. They are really reaching for a happy ending with that language.

I do not disagree that the reduced sensitivity might be legit and of significant abstract interest. But it is important to put in context: they are presenting this desensitizing effect as a possible explanation for an efficacy of SMT that barely exists — which is not only widely known, but confirmed by their own data. They are in effect saying, "Okay, so we know that SMT doesn't really help people on average, but isn't it nifty how it reduces sensitization by one measure in a way that might explain how it works in a few people if that's actually even a thing?"

To be a little more generous about it, SMT may well have more profound benefits for some people, occasionally, maybe — but we don’t know why, and we don’t know how to identify those patients. (Imagine if we knew that antibiotics were only partially effective for 5% of infections… and we had no idea which ones.) This de-sensitizing effect might conceivably help to explain those experiences in the future. But it’s really not much to work with. Nor is it really plausible that a modest effect on heat sensitivity

I think this was bang on, though:

“Our findings suggest that SMT-related satisfaction is influenced by the context of the intervention and not necessarily the intervention itself or corresponding outcomes.”

One final thing: why didn’t the placebo-boosted group do better? I would mostly chalk that up to being a good example of the limited “power” of placebo. Placebo is nearly as amazing as it’s cracked up to be, and there are very plausible explanations why it might not have done much here, chiefly that background levels of faith in spinal adjustment are already quite high around the world — it’s a popular therapy — so encouragement may well have just been “preaching to the choir.”

~ Paul Ingraham

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

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 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. «But greater to what degree? Was it even a statistically significant difference, let alone clinically significant?» 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.

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