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.
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 those obtained during diagnostic and range of motion testing, and are much smaller than failure strains.”
“We conclude from this work that cervical SMT performed by trained clinicians does not appear to place undue strain on VA, and thus does not seem to be a factor in vertebro-basilar injuries.”
“In summary, the maximal strain values for the ROM testing at each segmental level were always greater than the corresponding strain values for the SMTs, suggesting that neck SMTs impose less stretch than turning your head, or extending your neck while looking up at the sky.”
“Therefore, based on the mechanical tests performed here, one should be able to conclude that stretching of VA during neck SMTs does not cause any damage of the VAs.”
“The VA is never really strained during spinal manipulative treatments but that the VA is merely taking up slack as the neck and head are moved during SMT, but that there is no stress and thus no possibility for microstructural damage.”
“The results from this study demonstrate that average and maximal VA strains during high-speed low-amplitude cervical spinal manipulation are substantially less than the strains that can be achieved during ROM testing for all vertebral artery segments.”
“We conclude that cervical spinal manipulations, as tested here, are safe from a mechanical point of view for normal, healthy VA.”
The Whiplash Injury Connection
Whiplash injury is a common cause of neck pain, headache, dizziness, etc. (17). These same symptoms are consistent with vertebral artery injury. As noted here, individuals with these symptoms often present to chiropractors looking for relief of their problems.
Could Whiplash Injury Be Responsible for Vertebral Artery Injury?
Studies implicating whiplash injury as causing vertebral artery injury have been found in the medical literature for six decades. Examples include:
In 1958 a study published in the Journal of the American Medical Association states (18):
“Very little slack exists in the vertebral artery and, during severe hyperextension and hyperflexion and especially during extreme lateral rotation, partial to complete obstruction of the vertebral artery has been demonstrated by arteriography.”
“The vertebral artery is the pipeline carrying blood and oxygen to the brain stem.”
“Angiography has shown constriction or occlusion of the vertebral artery in patients with persistent symptoms of vertigo, ataxia, headache, diplopia, and unsteadiness of gait.”
“A great majority of symptoms that have been designated as psychoneurotic, namely, attacks of vertigo, ataxia, diplopia, severe attacks of migraine-like headache, hemicrania with nausea and vomiting, and, at times disturbances of speech and swallowing, are all due to disturbed circulation of the vertebral artery after neck sprain.”
In 1995 a study was published in the American Journal of Roentgenology where the authors reviewed 37 cases of cervical spine injury with magnetic resonance angiography (MRA) (19). The authors concluded:
“Vertebral artery injuries due to major cervical spine trauma as determined by MR angiography are common.”
“Noninvasive assessment of the vertebral arteries by means of MR imaging should be an integral part of the evaluation of the acutely injured cervical spine.”
Also in 1995, a case report was published in the journal Stroke documenting a vertebral artery dissection and stroke following a whiplash trauma. The authors state (20):
“We conclude that the whiplash injury caused a lesion of the right vertebral artery.”
“We suggest that in patients with disturbances of the vertebrobasilar circulation, attention should be paid to occurrence of neck trauma in the preceding 3 months.”
In 1997 a study was published in the European Spine Journal where the researchers exposed seven fresh human cadavers to rear-end type whiplash collisions while measuring the stretch to their vertebral arteries. The authors note (21):
“Vertebral artery (VA) stretch during trauma is a possible pathomechanism that could explain some aspects of the whiplash symptom complex.”
The authors documented that the vertebral artery significantly exceeded its physiological range in every experiment completed, adding to the evidence the vertebral artery is injured during a whiplash trauma.
In 2000 a case study was published in the European Journal of Emergency Medicine (22). The authors document a case of vertebral artery dissection caused by a head-on type whiplash injury.
In 2002 a study was published in the journal Neurological Research where researchers reviewed 29 patients with vertebrobasilar dissections (VBD) to investigate the correlation between minor trauma and VBD (23). They discovered that whiplash injury may in fact result in vertebral artery dissection.
In 2003, a study published in the Canadian Journal of Neurological Sciences reviewed all consecutive cases of traumatic vertebrobasilar ischemia referred to a single neurovascular practice over 20 years, identifying 80 patients, categorized as follows (24):
“Recent media exposure of strokes from chiropractic manipulation have focused attention on traumatic vertebrobasilar ischemia. However, chiropractic manipulation, while the easiest cause to recognize, is probably not the most common cause of this condition.”
“Five were diagnosed as due to chiropractic manipulation, but the commonest attributed cause was motor vehicle accidents (MVAs), which accounted for 70 cases; one was a sports injury, and five were industrial accidents.”
“In some cases neck pain from an MVA led to chiropractic manipulation.”
“Traumatic vertebrobasilar ischemia is most often due to MVAs; the diagnosis is often missed, in part because of the delay between injury and onset of symptoms.”
“Though chiropractic manipulation is perhaps the best-known cause [alleged], it is important to recognize that MVAs are a much more common cause, which is often missed.”
In 2005 a study published in the Journal of Manipulative and Physiological Therapeutics compiled an extensive review of the literature pertaining to cervical spine manipulation vs. motor vehicle collision as causation of vertebral artery dissection (25). The authors state:
“Long-lasting abnormalities of blood flow velocity within the vertebral artery have been reported in patients following common whiplash injuries, whereas no significant changes in vertebral artery peak flow velocity were observed following cervical chiropractic manipulative therapy.”
“Perceived causation of reported cases of cervical artery dissection is more frequently attributed to chiropractic manipulative therapy procedures than to motor vehicle collision related injuries, even though the comparative biomechanical evidence makes such causation unlikely.”
“The direct evidence suggests that the healthy vertebral artery is not at risk from properly performed chiropractic manipulative procedures.”
In 2006, the European Spine Journal published a study in which the authors examined 20 patients to assess the correlation between vertigo or dizziness and the vertebral arteries after whiplash injury using MRA. Abnormal MRA findings were seen in 60%. They state (26):
“Whiplash injury is not only limited to neck injury but also brainstem injury that does not involve direct damage to the neck or head.”
“Our findings suggest that some subjects with persistent vertigo or dizziness after whiplash injury are more likely to have VBI on MRA.”
“VBI might be an important background factor to evoke cervical vertigo or dizziness after whiplash injury.”
In 2008, a study was published in the journal European Neurology which was to estimate the incidence of posttraumatic dissections of cervical arteries in patients with whiplash injury acquired in a car accident. The authors retrospectively analyzed the medical records of 500 patients with whiplash injury acquired in car accidents and searched for dissections of cervical arteries occurring within 12 months after injury. They identified eight such cases, or one per every 62 injured patients. Recall the risk from spinal manipulation is one per 5.8 million procedures. The authors note that this incidence makes the risk of artery dissection from whiplash injury 200 times greater that in the general population. The authors make these points:
“There is an increased risk of posttraumatic dissection and cerebrovascular events within 12 months after whiplash injury.”
“The victims of car accidents should be screened for arterial dissections.”
“The incidence of cervical arterial dissections in patients with whiplash injury was much higher than the overall incidence of cervical arterial dissections in the general population. Therefore, we assume a causal relationship between arterial dissection and cervical spine distortion injury.”
“Many dissections of cervical arteries remain clinically asymptomatic, and the association with a car accident is not recognized.”
“Motor vehicle collisions should be considered as a risk factor for cervical arterial dissections.”
“There is an association between whiplash injury with arterial dissection and delayed cerebrovascular events occurring months after a car accident.”
Spinal manipulation is a published risk factor for vertebral artery dissection and stroke.
The published literature agrees that the incidence of arterial dissection caused by manipulation is extremely rare, in fact so rare that most chiropractors would have to be in clinical practice for hundreds of years to statistically be associated with one such event.