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J R Soc Med. 2007 October; 100(10): 447.
PMCID: PMC1997272

Author's response

I am impressed by the flurry of interest in my systematic review (JRSM 2007:100:330-338).1 The commentators make several general and some specific points which deserve an answer.

General comments

Generally, the letter writers seem to think I should ‘take a more positive attitude’. Reviewing the risks of therapeutic interventions may look negative to those who make a living out of using them. However, in truth it is motivated by our desire to render our future health care safer. The commentators, I think, confuse ‘negative’ with ‘critical’, and I should point out that an uncritical scientist is a contradiction in terms.

Another general theme of these letters is the claim that I ‘indiscriminately’ used ‘low-level evidence’. Systematic reviews on safety issues always have to rely heavily on case reports, many of which lack sufficient detail and thus conclusiveness. Yet when case-reports accumulate (in the case of chiropractic about 700 incidents have been published), they can send an important signal. To ignore it because of the low-level argument would quite simply be irresponsible. Moreover, I did, of course, report high-level evidence where this was available; the problem here is that such evidence is scarce and fails to confirm the view that spinal manipulations are low-risk.

Several commentators criticize me for not discussing the frequency of serious adverse events and some even provide data of their own. They must have missed a whole section of my paper where I do discuss these issues. But let's look at their figures: Bolton and Thiel state that there are over 2,000,000 cervical spine manipulations each year. Our UK survey disclosed 35 serious adverse effects within one year (JRSM 2001;94:107-110).2 Under-reporting was 100% in our series; this renders the calculation of any incidence impossible, so let's be optimistic and assume it is only 90%. One severe adverse effect would thus occur in about 5,700 spinal manipulations. Assuming that, on average, patients receive about 30 spinal manipulations during the course of a treatment (three per session, 10 sessions per course), the figure would indicate that one in about 1,900 patients could experience a severe adverse effect. Of course, this is back of the envelope stuff, but it nevertheless might indicate that the true incidence of adverse events is quite different from what chiropractors believe.

There seems to be a general consensus amongst the letter writers that my conclusions were ‘unjustified’. So let me re-state them: ‘Spinal manipulation, particularly when performed on the upper spine, is frequently associated with mild to moderate adverse effects. It can also result in serious complications such as vertebral artery dissections followed by stroke. Currently, the incidence of such events is not known. In the interest of patient safety we should reconsider our policy towards the routine use of spinal manipulation.’ To reconsider policy is not to ban! But to ignore such data would be to fail the public's interest.

Specific comments

Several commentators make specific comments that cannot be left unchallenged. The Chairman of the GCC states that his institution ‘requires all chiropractors to explain to patients the risks and benefits’ of chiropractic. Langworthy et al. recently showed that ‘only 23% [of UK chiropractors] report always discussing serious risk’.3 Is Dixon implying that 77% of all UK chiropractors are being summoned before the GCC's disciplinary panel?

The President of the BCA accuses me of ‘misquotes and errors’ and of puffing up evidence ‘out of all proportion’. Should he not provide evidence for his allegation? He also asks whether we would ban injections because they cause inflammation and hurt—to which the answer must be yes, definitely, if these injections are not demonstrably effective!

Mr Johnson states that ‘systems are in place for adverse event reporting of spinal manipulation’. Yet the Chair of the NCOR confirms that ‘spinal manipulation is not currently subject to post-marketing surveillance’.

Professor Grunnet-Nilsson states that ‘at least 20 other papers’ have already addressed my topic. Does he mean to say that we therefore do not need to update our knowledge—which, of course, was the stated aim of my systematic review?

In conclusion, it is an important and positive move to keep potential risks of therapeutic interventions under close scrutiny. It is also good to discuss discrepancies of opinion openly. In doing so we should, however, abstain from ad hominem attacks and insults (e.g. ‘Professor Ernst... has a problem with chiropractic’ [Lewis], ‘Professor Ernst has published a so-called “systematic review”... unsubstantiated claims masquerading as a systematic review’ [Bolton and Thiel], ‘this... paper is embarrassing’... [Grunnet-Nilsson]). Scientific disputes are productive: mud battles are not.


Competing interests None declared.


1. Ernst E. Adverse effects of spinal manipulation: a systematic review. J R Soc Med 2007;100: 330-8 [PMC free article] [PubMed]
2. Stevinson C, Honan W, Cooke B, Ernst E. Neurological complications of cervical spine manipulation. J R Soc Med 2001;94: 107-10 [PMC free article] [PubMed]
3. Langworthy JM, le Flemming C. Consent or submission? The practice of consent within UK chiropractic. J Manipulative Physiol Ther 2005;28: 15-24 [PubMed]

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