Criterion
Assessment for the Association Between Cervical Manipulation and CAD
1. Strength of the association 2. Consistency of the association 3. Outcome specific to exposure
The association is modest.
Four of five class II and III studies demonstrate an association.
As seen in Cassidy et al., exposure to a primary care doctor and exposure to a chiropractor are equally likely to result in CAD [5] . In this case the outcome is not specific.
4. Temporal relationship
A temporal relationship is necessary but not sufficient to establish causation. In this case, the onset of symptoms following cervical manipulation is variable and often delayed.
5. Biological gradient
There are no data to support or refute a dose-response hypothesis.
Are there increased rates of CAD in regions with increased utilization of chiropractic manipulation? No relevant data are available to address this criterion.
6. Plausibility
Tests on human cadavers have revealed that vertebral artery strains during spinal manipulative therapy do not place significant strain on the vertebral artery [23] . A review of data related to this topic sponsored by the American Heart Association concluded that: “Current biomechanical evidence is insufficient to establish the claim that spinal manipulation causes [CAD], including data from a canine model showing no significant changes in [vertebral artery] lesions before and after cervical manipulation” [11] .
7. Coherence
8. Experimental evidence 9. Analogous to proven association
The available animal models do not support the association.
While severe trauma most certainly causes dissection, it may be debated whether the situation in chiropractic care is analogous.
TABLE 2: Hill’s criteria for assigning causation to association [22] .
CAD = Cervical artery dissection
In spite of the very weak data supporting an association between chiropractic neck manipulation and CAD, and even more modest data supporting a causal association, such a relationship is assumed by many clinicians. In fact, this idea seems to enjoy the status of medical dogma. Excellent peer reviewed publications frequently contain statements asserting a causal relationship between cervical manipulation and CAD [4,25,26] . We suggest that physicians should exercise caution in ascribing causation to associations in the absence of adequate and reliable data. Medical history offers many examples of relationships that were initially falsely assumed to be causal [27] , and the relationship between CAD and chiropractic neck manipulation may need to be added to this list.
2016 Church et al. Cureus 8(2): e498. DOI 10.7759/cureus.498
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