In his book "Galileo's Revenge," attorney Peter Huber describes "junk science" as "A hodgepodge of biased data, spurious inference, and logical legerdemain...It is a catalog of every conceivable kind of error: data dredging, wishful thinking, truculent dogmatism, and, now and again, outright fraud." (1)

An excellent example of "junk science" is the popular notion that chiropractic adjustments cause strokes.

Although individual case reports of adverse events following "manipulation" have been reported in the medical literature for decades, recent exposes in the popular media seem to have led some gullible patients (and more than a few chiropractors) to accept this premise at face value. Careful examination will reveal that these individuals have fallen prey to a classic case of "junk science."

A common error in logic is equating correlation with cause and effect. The fact that a temporal relationship exists between two events does not mean that one caused the other.

As Keating explained, "To mistake temporal contiguity of two phenomena for causation is a classic fallacy of reasoning known as 'post hoc, ergo propter hoc,' from the Latin meaning 'after this, therefore caused by this.'" (2)

Simple examples of the "post hoc, ergo propter hoc" fallacy include the notions that germs cause disease, or rats cause garbage. Consider the application of this fallacy in the case of chiropractic adjustments and strokes.

Lee attempted to obtain an estimate of how often practicing neurologists in California encountered unexpected strokes, myelopathies, or radiculopathies following "chiropractic manipulation." Neurologists were asked the number of patients evaluated over the preceding two years who suffered a neurologic complication within 24 hours of receiving a "chiropractic manipulation." 55 strokes were reported. The author stated, "Patients, physicians, and chiropractors should be aware of the risk of neurologic complications associated with chiropractic manipulation." (3)

What's wrong with this picture? Let's change "neurologic complications" to automobile accidents. Would it be reasonable to suggest that if 55 patients over the last two years had car accidents within 24 hours of seeing a chiropractor that the D.C. caused the accidents? Want to see how absurd this can get? Change "neurologic complications" to ice cream consumption. Or sleep. Or orgasm.

Is there anything we can do that would either strengthen or weaken a case of alleged causality? Yes. If we have reliable reporting, we can compare the number of times the event in question (in this case, strokes) occurs as a random event to the number of times the event occurs following the putative causative event (in this case, a "chiropractic manipulation").

In a letter to the editor of JMPT, Myler posed an interesting question: "I was curious how the risk of fatal stroke after cervical manipulation, placed at 0.00025% compared with the risk of (fatal) stroke in the general population of the United States." (4)

According to data obtained from the National Center for Health Statistics, the mortality rate from stroke was calculated to be 0.00057%. If Myler's data is accurate, the risk of death from stroke after cervical manipulation is less than half the risk of fatal stroke in the general population!

But is Myler's data accurate? His 0.00025% figure is from a paper by Dabbs and Lauretti. (5)

Their estimate is probably as good as any, since the basis for it was a reasonably comprehensive review of literature. Yet, there is potentially conflicting information which must be considered.

Jaskoviak reported that not a single case of vertebral artery stroke occurred in approximately five million cervical "manipulations" at The National College of Chiropractic Clinic from 1965 to 1980. (6)

Not one.

Osteopathic authors Vick et al reported that from 1923 to 1993, there were only 185 reports of injury out of "several hundred million treatments." (7)

All of the figures which I found concerning stroke following "manipulation" involve estimates, not hard data.

In the "Back Letter" it was wisely observed that, "In scientific terms, all these figures are rough guesses at best... There is currently no accurate data on the total number of cervical manipulations performed every year or the total number of complications. Both figures would be necessary to arrive at an accurate estimate. In addition, none of the studies in the medical literature adequately control for other risk factors and co-morbidities." (8)

But we're not finished yet.

Leboeuf-Yde et al suggested that there may be an over-reporting of "spinal manipulative therapy" related injuries. The authors reported cases involving two fatal strokes, a heart attack, a bleeding basilar aneurysm, paresis of an arm and a leg, and cauda equina syndrome which occurred in individuals who were considering chiropractic care, yet because of chance, did not receive it. (9)

Had these events been temporally related to a chiropractic office visit, it is likely that they would have been inappropriately attributed to the chiropractic care.

Furthermore, there are cases of strokes attributed to chiropractic care where the "operator" was not a chiropractor at all.

Terrett observed that "manipulations" administered by a Kung Fu practitioner, GPs, osteopaths, physiotherapists, a wife, a blind masseur, and an Indian barber were incorrectly attributed to chiropractors. (10)

As Terrett wrote, "The words chiropractic and chiropractor have been incorrectly used in numerous publications dealing with SMT injury by medical authors, respected medical journals and medical organizations. In many cases, this is not accidental; the authors had access to original reports that identified the practitioner involved as a non-chiropractor. The true incidence of such reporting cannot be determined. Such reporting adversely affects the reader's opinion of chiropractic and chiropractors."

Alas, we're still not done.

Another error made in these reports is failure to differentiate "cervical manipulation" from specific chiropractic adjustment. They're simply not the same.

Klougart et al published risk estimates which reveal differences depending upon the type of technique used by the chiropractor. (11)

There is simply no competent evidence that specific chiropractic adjustments, or even "cervical manipulations" cause strokes. This conclusion begs the question, "What about screening tests to identify patients at risk?" More smoke and mirrors.

After examining 12 patients with dizziness reproduced by extension-rotation and 20 healthy controls with Doppler ultrasound of the vertebral arteries, Cote et al concluded, "We were unable to demonstrate that the extension-rotation test is a valid clinical screening procedure to detect decreased blood flow in the vertebral artery. The value of this test for screening patients at risk of stroke after cervical manipulation is questionable." (12)

Terrett noted, "There is also no evidence which suggests that positive tests have any correlation to future VBS (vertebrobasilar stroke) and SMT (spinal manipulative therapy)." (13)

Despite this, attorneys continue to file stroke related lawsuits against chiropractors, and muckrakers masquerading as journalists stir the emotions of the populace. It is time to put the misconception that chiropractic adjustments cause strokes to rest.

It's junk science.

References

1. Huber PW: "Galileo's Revenge. Junk Science in the Courtroom." Basic Books. 1991. Page 3.

2. Keating JC Jr: "Toward a Philosophy of the Science of Chiropractic." Stockton Foundation for Chiropractic Research, 1992. Page 189.

3. Lee K: "Neurologic complications following chiropractic manipulation: a survey of California neurologists." Neurology 1995;45:1213.

4. Myler L: Letter to the editor. JMPT 1996;19:357.

5. Debbs V, Lauretti WJ: "A risk assessment of cervical manipulation vs. VSAIDS for the treatment of neck pain." JMPT 1995;18:530.

6. Jaskoviac P: "Complications arising from manipulation of the cervical spine." JMPT 1980;3:213.

7. Vick D, McKay C, Zengerie C: "The safety of manipulative treatment: review of the literature from 1925 to 1993." JAOA 1996;96:113.

8. "What about serious complications of cervical manipulation?" The Back Letter 1996;11:115.

9. Leboeuf-Yde C, Rasmussen LR, Klougart N: "The risk of over-reporting spinal manipulative therapy-induced injuries; a description of some cases that failed to burden the statistics." JMPT 1996;19:536.

10. Terrett AGJ: "Misuse of the literature by medical authors in discussing spinal manipulative therapy injury." JMPT 1995;18:203.

11. Klougart N, Leboeuf-Yde C, Rasmussen LR: JMPT 1996;19:371.

12. Cote P, Kreitz B, Cassidy J, Thiel H: "The validity of the extension-rotation test as a clinical screening procedure before neck manipulation: a secondary analysis." JMPT 1996;19:159.