Cervical artery dissection: a biomechanical perspective.

Introduction Although there has been a putative link between cervical spinal manipulative treatment (cSMT) and cervical artery dissection (CAD) ever since Thornton’s report in the literature in 19341, recent evidence suggests that this is an association rather than a causal relationship. Since 2008, several studies published by Cassidy and co-workers2-4 have attributed the association between cSMT and CAD to patients seeking chiropractic care for neck pain and headaches during the prodrome of a stroke. Most reviews in the literature now generally report that there are no convincing data, either to prove or disprove, any causality between cSMT and CAD.5 However, case reports and case series still accumulate that identify chiropractic as the sole cause of CAD.6-7 Furthermore, Tuchin8 recently tested the causality between CAD and SMT using Hill’s criteria, and concluded that there is no evidence that SMT is causally related to stroke. Nevertheless, some authors continue to claim that cSMT causes CAD. Rather than using an epidemiologic approach to assess the risk of whether cSMT can cause CAD, another approach is to investigate the mechanism(s) of how cSMT can cause CAD. Since 20029, our laboratory has focused on the latter strategy. Using cadaveric vertebral arteries (VAs) as a model for the in vivo neck, we have measured the strains experienced by VAs using ultrasonography to dynamically measure the changes in VA segment lengths during manipulative procedures. The details of the experimental procedures have been described elsewhere.9-11 We have now replicated these experiments on a total of 16 VAs obtained from 10 cadavers9-11 in 3 different papers. Please note that we were unable to pool these data due to statistical considerations and advances in the experimental procedure. More recently, we have extended these experiments to investigate the strains experienced by the internal carotid artery (ICA) during cSMT utilizing essentially the same experimental protocol.12 Table 1 shows a summary of the data obtained thus far. The mechanical engineering strains experienced by the V3 segment of the VA, the segment which exits from the C2 transverse foramen and loops around C1 into the foramen magnum, during a Diversified-style cervical manipu-