Systematic Review and Meta-analysis of Chiropractic Care and Cervical Artery Dissection: No Evidence for Causation

Abstract

BackgroundCase reports and case control studies have suggested an association between chiropractic neck manipulation and cervical artery dissection (CAD), but a causal relationship has not been established. We evaluated the evidence related to this topic by performing a systematic review and meta-analysis of published data on chiropractic manipulation and CAD.MethodsSearch terms were entered into standard search engines in a systematic fashion. The articles were reviewed by study authors, graded independently for class of evidence, and combined in a meta-analysis. The total body of evidence was evaluated according to GRADE criteria.ResultsOur search yielded 253 articles. We identified two class II and four class III studies. There were no discrepancies among article ratings (i.e., kappa=1). The meta-analysis revealed a small association between chiropractic care and dissection (OR 1.74, 95% CI 1.26-2.41). The quality of the body of evidence according to GRADE criteria was “very low.”ConclusionsThe quality of the published literature on the relationship between chiropractic manipulation and CAD is very low. Our analysis shows a small association between chiropractic neck manipulation and cervical artery dissection. This relationship 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 and with chiropractic manipulation. There is no convincing evidence to support a causal link between chiropractic manipulation and CAD. Belief in a causal link may have significant negative consequences such as numerous episodes of litigation.

Does case misclassification threaten the validity of studies investigating the relationship between neck manipulation and vertebral artery dissection stroke? Yes

“…Therefore, inaccurate assignment of exposure to the putative trigger (SMT) is possible, and recall bias may have contributed to their data given the study design. A recent meta-analysis pooling all published studies found a nearly two fold higher risk of CAD associated with SMT [33]. But when limited to the 4 studies with imaging confirmation of cervical arterial dissection as the endpoint, SMT was associated with a significant 4-fold increase in risk [34].…”

“…Given the prevalence of SMT exposure (~8 % of adults and ~3 % of children annually) [38], even a modest increase in risk of dissection associated with SMT [33] could translate to thousands of avoidable dissections and strokes worldwide each year. So, on a population level, even a modest association between SMT and CAD could translate into a meaningful impact on public health.…”

“…So, on a population level, even a modest association between SMT and CAD could translate into a meaningful impact on public health. While there are several methodological challenges to this question [33, 39]-including accurate measurement of SMT procedures, and reverse causation-valid case classification should be a top priority. There are several ways forward to address the data quantity-quality tradeoff.…”

Does case misclassification threaten the validity of studies investigating the relationship between neck manipulation and vertebral artery dissection stroke? No

“…These data suggest that the most plausible explanation for the association between visits to chiropractors and VAD is that CMT is not a cause of VAD [11], but rather that patients who experience neck pain and/or headache resulting from the arterial dissection seek the services of a practitioner of CMT for relief of this pain, then go on to develop a stroke after this visit, independent of the CMT. This would also explain the similar associations of stroke between chiropractic and PCP patients; some patients with these symptoms will see their PCP and others a chiropractor.…”

“…Control for what Church et al [11] refer to as “interviewer bias.” Because of the highly publicized nature of many case reports and anecdotes about the relationship between visits to practitioners of CMT and stroke, emergency department physicians and neurologists who see patients with posterior circulation stroke may be more likely to attribute such a stroke to VAD resulting from CMT. Thus, many cases may be erroneously coded as VAD in the administrative database.…”