Terminology
Dissection:
A disruption or tearing of the inner layer of an artery.
Embolus (singular) or emboli (plural):
An arterial dissection may form a clot that is capable of lodging free and traveling down the source artery.
Stroke:
When a traveling embolus plugs and disrupts arterial blood flow, it is known as a stroke. Strokes result in a variety of neurological signs and symptoms.
Modern chiropractors are extensively trained about the anatomy and mechanical physiology of the vertebral artery, particularly as related to dissection and stroke. In reviewing the literature on the topic, several central themes become apparent:
Estimates of the incidence of alleged injury to the vertebral artery from spinal manipulation is extremely rare, so rare that it is extremely difficult to quantify and extremely difficult to study. An estimate of the incidence appeared in the 2004 book Neck Pain, published by the American Academy of Orthopedic Surgeons a (1). The authors state:
“Major complications from manual therapies are extremely rare but, nonetheless, have been a source of much discussion.”
“Estimates of vertebral artery dissections or stroke rates associated with cervical manipulation have ranged from 1 per 400,000 to 1 per 10 million manipulations.”
“An estimate of 1 per 5.85 million manipulations, based on 1988 to 1997 medical record and chiropractic malpractice data from Canada, reflects the experience of practitioners of manipulation.”
“No serious complications from spinal manipulation or other chiropractic forms of manual treatment have been reported from any of the published clinical trials involving manipulation or mobilization for neck pain.”
“It should be noted that complications rates from medications, surgery, and most other neck pain treatments for which data are available are estimated to be higher than those from manual and manipulative therapies.”
When it is alleged that spinal manipulation causes a vertebral artery dissection, much of the published literature on the topic considers “chiropractic” and “manipulation” to be synonymous. Chiropractors are extensively trained in the science and art of manipulation, while lay practitioners often are not. Reported case study analysis shows that when an untrained person manipulates a patient and allegedly causes an injury, the literature often inappropriately labels the manipulator as being a chiropractor (2). The list of discovered manipulators included:
A published review concluded (2):
“This study reveals that the words chiropractic and chiropractor commonly appear in the literature to describe spinal manipulative therapy, or practitioner of spinal manipulative therapy, in association with iatrogenic complications, regardless of the presence or absence of professional training of the practitioner involved.”
“The words chiropractic and chiropractor have been incorrectly used in numerous publications dealing with spinal manipulative therapy injury by medical authors, respected medical journals and medical organizations.”
“In many cases, this is not accidental; the authors had access to original reports that identified the practitioner involved as a non-chiropractor. The true incidence of such reporting cannot be determined.”
“Such reporting adversely affects the reader’s opinion of chiropractic and chiropractors.”
“It has been clearly demonstrated that the literature of medical organizations, medical authors and respected, peer-reviewed, indexed journals have, on numerous occasions, misrepresented the facts regarding the identity of a practitioner of manual therapy associated with patient injury.”
“Such biased reporting must influence the perception of chiropractic held by the reader, especially when cases of death, tetraplegia and neurological deficit are incorrectly reported as having been caused by chiropractic.”
“Because of the unwarranted negative opinion generated in medical readers and the lay public alike, erroneous reporting is likely to result in hesitancy to refer to and underutilization of a mode of health care delivery.”
This misuse of the literature, attributing manipulation vascular accidents to a chiropractor when in fact the manipulation was not performed by a chiropractor continues, as does the rebuttals designed to set the record straight (3, 4, 5).
Pre-manipulation tests designed to screen for individuals who might have an increased risk of a vascular injury as a consequence of a spinal manipulation are often non-revealing; such testing does not adequately identify patients who may have an increased risk of injury.
For example, a 2002 study (6), published in the journal Spine, was a retrospective review of 64 medicolegal records describing cerebrovascular ischemia after cervical spine manipulation. The authors note, that up to the publication of their article in 2002, only about 117 cases of post-manipulation cerebrovascular ischemia had been reported in the English language literature.
The authors further indicate that proposed risk factors for cerebrovascular ischemia secondary to spinal manipulation include age, gender, migraine headaches, hypertension, diabetes, birth control pills, cervical spondylosis, and smoking, and that it is often assumed that these complications may be avoided by clinically screening patients and by pre-manipulation positioning of the head and neck to evaluate the patency of the vertebral arteries. However, after an extensive review, these authors conclude:
“This study was unable to identify factors from the clinical history and physical examination of the patient that would assist a physician attempting to isolate the patient at risk of cerebral ischemia after cervical manipulation.”
“Cerebrovascular accidents after manipulation appear to be unpredictable and should be considered an inherent, idiosyncratic, and rare complication of this treatment approach.”
Additional, more recent studies have arrived at similar conclusions (7, 8, 9, 10).
Recent large studies, looking at millions of follow-up years and/or millions of participants are indicating that chiropractic spinal manipulation does not cause vertebral artery dissection, but that in contrast the patient is presenting to a chiropractic office in the middle of spontaneous dissection of the artery.
A 2008 study published in the journal Spine included all residents of Ontario, CAN, over a period of 9 years, amounting to more than 109 million person years of observation. The authors noted (11):
“We found no evidence of excess risk of vertebral artery stroke associated with chiropractic care.”
“Neck pain and headache are common symptoms of vertebral artery dissection, which commonly precedes vertebral artery stroke.”
“The increased risks of vertebral artery stroke associated with chiropractic and primary care physicians visits is likely due to patients with headache and neck pain from vertebral artery dissection seeking care before their stroke.”
“Because patients with vertebrobasilar artery dissection commonly present with headache and neck pain, it is possible that patients seek chiropractic care for these symptoms and that the subsequent vertebral artery stroke occurs spontaneously, implying that the association between chiropractic care and vertebral artery stroke is not causal.”
“Our results suggest that the association between chiropractic care and vertebral artery stroke found in previous studies is likely explained by presenting symptoms attributable to vertebral artery dissection.”
A 2011 study published in the Journal of Manipulative and Physiological Therapeutics used a population-based case series with administrative health care records of all Ontario, CAN, residents hospitalized with vertebral artery stroke between April 1, 1993, and March 31, 2002. These authors note (12):
“The current evidence suggests that association between chiropractic care and vertebrobasilar artery (VBA) stroke is not causal. Rather, recent epidemiological studies suggest that it is coincidental and reflects the natural history of the disorder.”
“Because neck pain and headaches are symptoms that commonly precede the onset of a VBA stroke, these patients might seek chiropractic care while their stroke is in evolution.”
In a 2011 editorial published in The Open Neurology Journal noted (13):
“The current best-evidence indicates no causal relationship between spinal manipulation (‘chiropractic maneuver’) and vertebrobasilar artery (VBA) stroke.”
“Evidence is mounting that the association between spinal manipulation and stroke is coincidental rather than causal and reflects the natural history of the disorder.”
“The prevailing hypothesis is that patients with vertebral artery dissections often have initial symptoms that cause them to seek care from a chiropractic or medical physician and the stroke is independent of their visit.”
“The latest scientific evidence questions whether spinal manipulation is a risk factor at all for cervical artery dissection.”
“Chiropractic spinal manipulations may very well be a demerging risk factor for stroke since there may not be any risk.”
“The evidence, albeit limited to date, suggests that spinal manipulative treatments produce stretches of the vertebral artery that are much smaller than those that are produced during normal everyday movements, and thus they appear harmless.”
A 2015 study published in the journal Chiropractic & Manual Therapies, assessed commercially insured and Medicare Advantage (MA) health plan members in the U.S. The data set encompassed 35,726,224 commercial and 3,188,825 MA members, therefore looking at approximately 39 million people, making this the largest case–control study to investigate the association between chiropractic manipulation and vertebral artery stroke. These authors concluded (14):
“There was no association between chiropractic visits and VBA stroke found for the overall sample, or for samples stratified by age.”
“We found no significant association between exposure to chiropractic care and the risk of vertebral artery stroke. We conclude that manipulation is an unlikely cause of vertebral artery stroke.”
A 2016 study published in the journal Cureus evaluated the evidence by performing a systematic review and meta-analysis of published data on chiropractic manipulation and cervical artery dissection (CAD). These authors state (15):
“We found no evidence for a causal link between chiropractic care and CAD. This is a significant finding because belief in a causal link is not uncommon, and such a belief may have significant adverse effects such as numerous episodes of litigation.”
“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. 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, and the relationship between CAD and chiropractic neck manipulation may need to be added to this list.”
“There is no convincing evidence to support a causal link, and unfounded belief in causation may have dire consequences.”
“The association between a chiropractor visit and dissection may be explained by” understanding that “patients with cervical artery dissection more frequently have headache and neck pain” and understanding that “patients with headache and neck pain more frequently visit chiropractors.”
“Because (on average) patients with headache and neck pain visit chiropractors more frequently, and patients with cervical artery dissection more frequently have headache and neck pain, it appears that those who visit chiropractors have more cervical artery dissections.”
Globally, there is only one lab engaging in primary research to assess the biomechanical risk of cervical spinal manipulation and vertebral artery dissection. This research is being done at the University of Calgary, CAN, and is headed by Walter Herzog, PhD. In 2012, Dr. Herzog and colleagues published a study in the Journal of Electromyography and Kinesiology presenting the first ever data on the mechanics between C1/C2 during cervical manipulation performed by chiropractic clinicians (16). These authors concluded:
“VA strains obtained during SMT are significantly smaller than tho