by Gary Lyons

Spinal manipulation: underwhelming effects on back pain since 1895.

Recently I posted a quick link to this new review of spinal manipulative therapy, and promised to say a little more about it later. It’s time …

A new Cochrane review?The Cochrane Collaboration publishes comprehensive reviews of what the science can tell us so far about medical treatments, and they promote and facilitate evidence-based medicine. Although not perfect — in recent years their quality control has slipped a little — they still generally produce the most authoritative reviews available about musculoskeletal health care. of all the science so far reported that spinal manipulative therapy (SMT) for low back pain is “no better or worse” than other therapies … which damns it with very faint praise, of course, because no therapy has ever been shown to be all that effective for low back pain. The authors concluded: “High quality evidence suggests that there is no clinically relevant difference between spinal manipulative therapy and other interventions for reducing pain and improving function in patients with chronic low-back pain.”

None of this is really new. The results are just a mashup of all the studies I’ve reported on before, and this review is actually an update of an older one that includes data from the last few years. There has never been a ringing scientific endorsement of SMT, and that was clear to anyone following along. But Cochrane reviews have a solid reputation, and it’s good to have a careful summary of the science like this.

The conclusion to this review rings positive to many readers: “as good as” other therapies sounds good. It’s really not. The story of low back treatments is really quite depressing: the evidence is overwhelming that almost nothing really works. Massage has the strongest evidence of efficacy of any treatment for low back pain that I know of — so says another Cochrane review, see Furlan et al, and many of the crankiest skeptics have acknowledged this — but I’m afraid even that’s not exactly working any miracles.

What is spinal manipulative therapy?

Is this chiropractic therapy we’re talking about? Yes and no. Lots of physical therapists do SMT, but quite different in spirit. Spinal manipulative therapy is a rather broad term encompassing nearly any manual, hands-on treatment of spinal joints, any kind of strategic “wiggling” to stimulate and loosen them. It includes:

both manipulation and mobilisation. In manual mobilisations, the therapist moves the patient’s spine within their range of motion. They use slow, passive movements, starting with a small range and gradually increasing to a larger range of motion. Manipulation is a passive technique where the therapist applies a specifically directed manual impulse, or thrust, to a joint, at or near the end of the passive (or physiological) range of motion. This is often accompanied by an audible ‘crack.’

SMT includes chiropractic spinal adjustment, and this is the type of SMT that most consumers will encounter in the wild, but SMT is not just chiropractic: many other professionals also employ spinal manipulative therapy, especially physical therapists, and typically do so for quite different reasons, and with different methods. For instance, many chiropractors believe that they are “adjusting” and “re-aligning” the spine with benefits for general health and not just back pain, but this is anatomically impossible and scientifically indefensible, and very few (if any) physical therapists use SMT with that intention.

Better quality evidence than we’re used to

There is usually an exasperating absence of evidence about manual therapies, and reviews like this usually must conclude with tentative conclusions and lame more-research-needed disclaimers. Happily, SMT is an exception.

…we identified 26 randomised controlled trials (represented by 6070 participants) that assessed the effects of SMT in patients with chronic low-back pain. Treatment was delivered by a variety of practitioners, including chiropractors, manual therapists and osteopaths. Only nine trials were considered to have a low risk of bias. In other words, results in which we could put some confidence.

Indeed: the huge numbers of participants and several unbiased trials is important and unusual in this field. It’s usually just the opposite, with amazingly few study subjects and an alarming risk of bias in nearly every trial — low quality studies conducted almost exclusively by amateur scientists (clinicians) who are basically doing the research in the hopes that it will prove that their own methods work, and darned if they don’t find a way to make their results seem positive. But … garbage in, garbage out!

So this is different. Mostly because of the (controversial) popularity of chiropractic, SMT has really been in the spotlight, and a lot of really good quality experiments have been done. The collective data is pretty substantive.

Could benefits of some SMT have been “washed out”?

A fair criticism of this review is that it lumps together too many kinds of SMT for too many different kinds of patients. What if SMT works really well when done one way, with one kind of patient, but quite poorly otherwise? This is definitely an chronic issue with reviews of this type, where the results of many different scientific experiments are considered en masse: real benefits in specific situations might disappear or “wash out” when mixed in with too many other scenarios where a therapy is doomed to failure.

Indeed, this line of reasoning is a highly predictable reaction from practitioners who have a financial stake in the reputation of spinal manipulative therapy.

On the other hand, any truly worthwhile benefits to SMT in any situation should be obvious, noteworthy, and more than capable of standing out and pulling up the average. So while I concede that modest real benefits of SMT might get obscured and overshadowed in a big review, I doubt that significant benefits would ever vanish into the statistics.

Thus we are still left with SMT being damned with faint praise here. If there are certain kinds of SMT that work extremely well on certain kinds of patients, it sure does not show in this data, and this review considered all the best studies that have ever been done. As Neil O’Connell of Body in Mind described these results: “a tiny effect size for manipulation that doesn’t really tickle the undercarriage of clinical significance.”

Indeed — and this is the clincher — there is no individual study that I know of that shows any significant benefit. If any specific flavour of SMT works especially well for any particular type of patient, that combination was not studied in any of the 26 experiments covered by this Cochrane review.