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Cervical Artery Dissection

Several studies have shown that evidence is lacking for a causal relationship between cervical spine manipulation and cervical artery dissection. Recently, another systematic review and meta-analysis conducted within the Department of Neurosurgery at Penn State Hershey Medical Center independently came to the same conclusion (1). Study authors found an association between a visit to a doctor of chiropractic and cervical artery dissection, but no evidence for causation.

How there can be an association without evidence for causation? To illustrate this concept, the authors included a list of 9 tests first postulated by Sir Austin Hill. These logical tests are considered necessary to conclude causation when only an association can be found (2). While applying current evidence to these tests, the authors found only 1 passed, 4 failed, and 4 others were ambiguous due to a scarcity of analyzable data. This doesn’t mean there is no possibility that manipulation causes or increases the risk for cervical artery dissection. However, the preponderance of evidence suggests there likely isn’t a causal element. A summary of the 9 tests is listed below.

1. Strength of association: Only modest strength of association exists for cervical manipulation and arterial dissection

2. Consistency of association: 4 of 5 studies demonstrate an association

3. Outcome specific to exposure: Exposure to chiropractic and primary care doctors equally results in likelihood of cervical arterial dissection. Therefore, the outcome is not specific to exposure.

4. Temporal relationship: Onset of symptoms following cervical manipulation varies and are often delayed, thus reducing the likelihood of a consistent injury mechanism

5. Biological gradient: No data are available to support or refute a dose-response effect

6. Plausibility: No data exists to evaluate whether increased rates of cervical artery dissection occur with increased chiropractic care utilization.

7. Coherence: Human cadaveric testing have revealed cervical artery strains are not substantial during cervical manipulation.

8. Experimental evidence: Animal research evidence does not support the association

9. Analogous to proven association: Severe trauma is known to cause cervical artery dissection. However, cervical manipulation is not analogous to severe trauma, especially given the millions of treatments provided annually and clinical trial evidence suggesting adverse events are mostly mild.

References

1. Church E W, Sieg E P, Zalatimo O, et al. (February 16, 2016) Systematic Review and Meta-analysis of
Chiropractic Care and Cervical Artery Dissection: No Evidence for Causation. Cureus 8(2): e498. DOI
10.7759/cureus.498
2. Hill AB: The environment and disease: association or causation?. Proc R Soc Med. 1965,
58:295–300.

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