The result: they found no evidence for causation. Here are the details on a contentious issue.
The authors of the study all hailed from the neurosurgery departments of either Penn State Hershey Medical Centre, Loma Linda University Medical Center or Pennsylvania State University. They undertook to examine the case reports and case control studies that suggested an association between chiropractic neck manipulation and cervical artery dissection by means of a systemic review and meta analysis .
They used a GRADE rating to establish the quality of the evidence[2,3,4]. This starts by examining the study design, before looking sequentially at features with potential to enhance or diminish confidence. The eventual rating took into consideration potential for bias given the controversial nature of the topic and the legal ramifications of the study’s findings. This is where it gets interesting.
The search took them through some 253 articles with just two eligible class II and four class III studies among the number. Though the meta-analysis seemed to reveal a small association between chiropractic care and dissection, the authors of the study deemed the evidence to be of ‘very low’ quality according to the GRADE rating.
This lead the authors to reason that the relationship (between chiropractic care and CAD) may be explained by “the high risk of bias and confounding in the available studies, and in particular by the known association of neck pain with CAD [cervical artery dissection] and with chiropractic manipulation and CAD. Belief in a causal link may have significant negative consequences such as numerous episodes of litigation .”
Once again, it appears that the truth may be getting in the way of a good story when it comes to so-called ‘risks’ tied up with chiropractic. The existing literature pointing to a correlation between spinal manipulative therapy and CAD is, according to the researchers, very low quality and potentially loaded with bias.
“While this study controlled for possible confounders such as neck pain, there were several limitations. Head and neck pain as well as chiropractor visit were assessed in a retrospective fashion by mail survey, very possibly introducing both recall and survivor bias. The reason for reporting to the chiropractor (e.g., trauma) was not assessed. Further, there was significant variability among diagnostic procedures, which may reflect increased motivation by physicians to rule out dissection in patients with a history of SMT. Such motivation could result in interviewer bias,” they wrote .
This isn’t just a study that failed to dig up any evidence. It’s a study that points to a potentially serious misconception. The authors wrote:
“There is no convincing evidence to support a causal link, and unfounded belief in causation may have dire consequences .”
So there you have it. Chiropractic care and cervical artery dissection, at this point in time, there is no evidence for causation.
 Church E, Sieg E, Zalatimo O, Hussain N, Glantz M, Harbaugh R (2016) “Chiropractic Care and Cervical Artery Dissection: No Evidence for Causation,” Penn State Neurosurgery Channel, http://www.cureus.com/articles/4155-systematic-review-and-meta-analysis-of-chiropractic-care-and-cervical-artery-dissection-no-evidence-for-causation retrieved 29 March 2017
 Guyatt G, Oxman AD, Akl EA, et al.: GRADE guidelines: 1. Introduction-GRADE evidence profiles and summary of findings tables. J Clin Epidemiol. 2011, 64:383–394. 10.1016/j.jclinepi.2010.04.026
 Guyatt GH, Oxman AD, Kunz R, et al.: GRADE guidelines: 2. Framing the question and deciding on important outcomes. J Clin Epidemiol. 2011, 64:395–400. 10.1016/j.jclinepi.2010.09.012
 Balshem H, Helfand M, Schünemann HJ, et al.: GRADE guidelines: 3. Rating the quality of evidence. J Clin Epidemiol. 2011, 64:401–406. 10.1016/j.jclinepi.2010.07.015