Cervical manipulation: How risky is it?

The commentary by John Norris and colleagues¹ is an excellent example of pseudoscience.

The data in this article were collected retrospectively, not prospectively as suggested by Norris and the media. This type of research is fraught with examination bias.

The most obvious error is the equation of correlation or temporal coincidence with cause and effect. Norris and colleagues claim that 21 of 74 cases of stroke (28%) were caused by cervical manipulation by a chiropractor. What if the term “automobile accidents” was substituted for “stroke”? If 21 patients over the last year had car accidents after seeing a chiropractor, would it be reasonable to suggest that the chiropractor caused the accidents?

What criteria did the authors use for including patients in their survey? What was the cut-off time after chiropractic adjustment? Would it not be absurd to include patients who had visited a chiropractor 95 days, or even 6 days, before the arterial dissection? How many other confounding variables did they control for? What if a patient had a chiropractic adjustment and later that day went to their dentist or had their hair washed at a beauty parlour and then 2 days later had a violent sneeze or cough followed by a stroke?

The authors state that if a patient has neck pain after a chiropractic manipulation it represents an arterial dissection. I would like to see some hard evidence to support this statement. Some patients have neck pain after chiropractic adjustment because their spines are badly misaligned with a concomitant inflammatory process and there sometimes is correctional stress after the adjustment, such as the stress an orthodontist would create when adjusting braces.

Finally, what is the mandate of the Canadian Stroke Consortium? Have the members of the consortium applied as much effort to the study of other causes of stroke, such as adverse reactions to drugs, as they have to their study of adverse events caused by chiropractic?

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Alan O'Connor
Chiropractor Ayr, Ont.