In medicine interventions are assessed according to the principle of risk versus benefit. Interventions are never risk free, so that is not a reasonable criterion for a valid intervention (whether therapeutic, symptomatic, or diagnostic). Rather the benefit provided by the intervention must be substantially greater than the risk.
Related to this is the principle that the alternative with the lowest risk (assuming similar benefit) should always be preferred. For this reason the standard of care is always shifting as new evidence comes in altering the relative risk versus benefit calculation of available options. At least that is what happens within mainstream medicine.
The above, in my opinion, does not happen within the world of so-called complementary and alternative medicine (CAM), because of a philosophical opposition to the application of rigorous scientific standards in medicine (whether or not individual CAM proponents admit this). In fact the only purpose of the CAM category is to market and promote medical practices that are not supported by good science.
Neck manipulation, mostly performed by chiropractors, is an excellent example of this. Neurologists have been warning for years of growing evidence that neck manipulation carries a risk of stroke and death from trauma to the neck arteries. Chiropractors have generally denied or minimized this risk. A recent article in the BMJ (British Journal of Medicine) reviews this controversy and concludes that neck manipulation, based upon relative risk vs benefit, should be abandoned as a therapy.
The risk of high cervical manipulation or the violent and rapid neck manipulation mostly performed by chiropractors (90%) is that it will cause a tear (called a dissection) in a carotid or vertebral artery feeding the brain. Blood can then clot around the tear, and that clot can break off and lodge distally in the brain, causing a stroke. In this manner strokes causing serious debility or even death can result in young and otherwise healthy individuals.
The magnitude of this risk is a matter of some debate. There are no controlled clinical trials where patients are randomized to neck manipulation versus other therapies. We therefore have to rely on retrospective data - looking at patients with dissection to see if they were more likely to have had recent neck manipulation, or looking at those with neck manipulation to see if they are more likely to have a dissection. There are a number of weaknesses with this type of data, however. Dissection following neck manipulation is definitely under-diagnosed and under-reported, the only question is by how much. The connection to recent chiropractic manipulation may not always be made.
Further, the correlations found in this type of data does not necessarily indicate cause and effect. Chiropractors have claimed that patients with dissection have neck pain and seek chiropractic care for this neck pain, resulting in the correlation. This cannot be assumed, however, and this is also not a justification for neck manipulation. Even if correct it would mean that chiropractors are missing the diagnosis of arterial dissection and manipulating patients who have a dissection - something which is dangerous and contraindicated itself. This is hardly, therefore, a defense of neck manipulation.
In any case, estimates of the risk of arterial dissection from neck manipulation vary, but are definitely low. The overall rate of vertebral artery dissection is 1-1.7 per 100,000 person years in the US, according to the BMJ article. Estimates for vertebral dissection resulting from neck manipulation range from 1 in 400,000 to 1 in 5.8 million manipulations. The 5.8 million figure is certainly an underestimate, as it is based on litigation records and not clinical cases. The 1 in 400,000 figure is more reliable, and itself is likely an underestimate. It should further be noted that this refers to manipulations, not patients, and one patient may undergo many manipulations during a course of treatment.
In absolute terms this is a low risk, and we certainly accept higher chances of adverse outcomes in many mainstream treatments. But we need to also consider that, while the chance may be low, the risk we are talking about is stroke or death - a very serious adverse outcome. Further, this may occur in young and otherwise healthy individuals. In that context, the risk is relative high for a medical intervention.
We therefore need to ask about the other side of the equation - what is the benefit? There too, it should come as no surprise, there is controversy. In my opinion the evidence is not controversial, only the interpretation of this evidence by the chiropractic community.
A number of recent systematic reviews of spinal manipulation in general (but including neck manipulation for headaches) have concluded that there is no evidence to support that they are effective for any indication. Looking specifically at cervical manipulation for headaches, systematic reviews are also negative. The reviews indicate that the best controlled studies are negative. The less rigorous studies are mixed. This is a familiar pattern, consistent with an ineffective treatment combined with researcher and publication bias.
The BMJ article is actually more favorable, concluding that there is evidence for short term symptomatic benefit from cervical manipulation. However, the evidence shows that the benefits are no better than safer treatments, such as massage, medication, or neck mobilization (a gentler intervention favored by physical therapists). A recent study, for example found that neck manipulation was no better than simply applying tape (Kinesiotaping) to the affected muscles. (It should be noted that there was no placebo group, so the study could not establish that either treatment was more effective than placebo.)
Therefore, at best neck manipulation provides short term benefit that is no better than other safer methods. That is a devastating assessment of any medical intervention, and certainly justifies abandoning that method.
Some critics of neck manipulation (such as Sam Homola linked to in the SBM article above) argue that it should not be abandoned completely but should be reserved for highly selective cases in which there is no contraindication and the safer treatments have been tried and found to be ineffective. This too is reasonable, but is still based upon the notion that neck manipulation has a significant benefit, which has not been established by rigorous clinical evidence.
The response of the chiropractic community so far has been predictable. The British Chiropractic Association is quoted by the BBC:
"The cherry-picking of poor quality research needlessly raises alarm in patients and does little to help the people suffering from neck pain and headaches to choose the most appropriate treatment."
As is typical of CAM apologists, they are begging the question - does neck manipulation help those suffering from neck pain? The answer, in my opinion and based on published systematic reviews (the very antithesis of cherry picking) is no. Further, claiming that a reasonable and thorough assessment of risk vs benefit is needlessly alarmist says volumes about the approach of the chiropractic community to their own practice and the scientific evidence.
My primary criticism of the CAM community in general, and the chiropractic profession specifically, is that they do not have a culture and philosophy of ethical science-based practice. If they did they would be practicing real medicine, not the "alternative." The issue of neck manipulation and risk of arterial dissection reflects this basic reality, and is not an isolated case but a systemic problem.
Steven Novella, M.D. is the JREF's Senior Fellow and Director of the JREF’s Science-Based Medicine project.
Dr. Novella is an academic clinical neurologist at Yale University School of Medicine. He is the president and co-founder of the New England Skeptical Society and the host and producer of the popular weekly science show, The Skeptics’ Guide to the Universe. He also authors the NeuroLogica Blog.