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The Vertebral Artery

The brain is supplied by blood from two arterial sources: the paired internal carotid arteries and the paired vertebral arteries. The blood supply to brain from the carotid arteries is referred to as the anterior circulation to the brain. The blood supply to brain from the vertebral arteries is referred to as the posterior circulation to the brain.

The vertebral arteries are exceptionally unique: they ascend to the brain through an opening, a foramen, in the transverse process of the cervical vertebrae.

This opening is called the foramen transversarium. The foramen transversarium exists in the cervical vertebrae C6-C1. The vertebral arteries ascend in the foramen transversarium before entering the skull through the foramen magnum.

After entering the skull, the paired vertebral arteries merge to become the singular basilar artery (drawing from reference 1).

The singular basilar artery ascends along the anterior surface of the brain stem, supplying its vascular needs through the pontine arteries. The basilar artery ends when it bifurcates into the paired posterior cerebral arteries (drawing from reference 1).

The posterior cerebral arteries form the posterior aspect of the Circle of Willis. The Circle of Willis is the unique anatomical location where the posterior circulation (originates with the vertebral arteries) and the anterior circulation (originates with the internal carotid arteries) to the brain amalgamate together.

The atlas-axis (C1-C2) vertebral articulation of the cervical spine is mechanically unique. It is designed for the function of rotational motion. When one maximally turns one’s head, approximately 55% of that motion occurs at the atlas-axis articulation. The vertebral artery in the foramen transversarium between the atlas and axis must accommodate this rotational motion. This places the vertebral artery at increased risk of tractional types of stress and potential injury as a consequence of a variety of upper cervical spine mechanical loads.

The potential tractional injury to the vertebral artery is a dissection, and usually referred to as vertebral artery dissection, or VAD.

Right cervical spine (head) rotation, showing the tension on the left vertebral artery between the atlas and axis (drawing from reference from 1).

Cervical arterial dissection is one of the main causes of ischemic stroke in young adults. Cervical arterial dissections can be categorized as traumatic or spontaneous. Cervical artery dissections occur when a tear forms in the tunica intima and blood enters into the space between intima and media. This can lead to a complete occlusion of the vessel lumen, which is mostly followed by recanalization after several months (2).

Approximately 2/3 of cervical artery dissections are spontaneous and approximately 1/3 of them are posttraumatic. The overall annual incidence of spontaneous and posttraumatic dissections of the carotid artery is 26 / 1 million. The incidence of vertebral arterial dissection (spontaneous and posttraumatic) is 15 / 1 million. As noted, spontaneous cervical artery dissections occur twice as often as posttraumatic cervical artery dissections (2).

Signs and symptoms that would warn of a possible vertebral artery dissection with ischemia are often summarized as the 5 Ds And the 3 Ns (1):

Dizziness (vertigo, light-headedness)

Drop attacks

Diplopia (or other visual problems)

Dysarthria [Speech Disorder]

Dysphagia [Difficult or Painful Swallowing]

Ataxia of gait (Hemiparesis)

Nausea (possibly with vomiting)


Numbness (hemianesthesia)

A history that would warn of a possible vertebral artery dissection with ischemia involves a sudden onset of severe head and/or neck pain, which is like no other pain the patient has previously suffered. This is especially important if the patient can isolate the pain to the suboccipital region (1).

According to a review of the literature by Alan Terrett (1), a number of non-manipulative mechanical events have been linked to vertebral artery dissections. These mechanical events usually involve rotation and/or extension, and include:


By Surgeon or Anesthetist During Surgery

Calisthenics, Athletics, Fitness Exercise


Overhead Work, Painting a Wall

Hanging Out the Washing

Neck Extension during Radiography

Neck Extension for a Bleeding Nose

Turning the Head while Driving a Vehicle

Tonic Clonic Convulsive Seizure

Amusement Park Ride

Protracted Dental Work


Sneezing/Nose Blowing/Coughing


Emergency Resuscitation

Star Gazing, Watching Aircraft

Sleeping Position


Break Dancing


Beauty Parlor Stroke, Sitting in a Barber’s Chair

Tai Chi

Sexual Intercourse

With respects to risk of vertebral artery dissection associated with cervical manipulation, all chiropractors are well aware of the issue. Vertebral artery dissection is extensively discussed in both chiropractic undergraduate and post graduate continuing educational programs. Entire books are written on the subject and are a part of core curriculum at chiropractic colleges (1). Chiropractors are well schooled on the pertinent anatomy, signs/symptoms, clinical presentations, examination findings, and procedures that may possibly be associated with increased risk. Although the risk of vertebral artery dissection is quite rare (as infrequent as 1/ 3,800,000 cervical manipulations in one study (4)), it appears to have a higher risk with the coupling of rotation with extension of the atlas (C1) on the axis (C2).

In an important article published in 1995 (3), Alan Terrett reviewed the published literature pertaining to the incidence of reported adverse events associated with chiropractic spinal adjusting (manipulation). Astonishingly, his results revealed that in many of the published adverse events ascribed to chiropractic manipulation were, in fact, not associated with chiropractic in any manner. Apparently, the authors of the articles assumed “chiropractic” and “manipulation” were synonyms. When untrained laypersons or physicians performed a manipulation resulting in a reported adverse event, authors would claim that the manipulation was performed by a chiropractor. The list of discovered manipulators included:

A Blind Masseur

An Indian Barber

A Wife

A Kung-Fu Practitioner

Self Manipulation

Often the manipulation was performed by a medical doctor, an osteopath, a naturopath, or a physical therapist.

Dr. Terrett concluded:

“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.”

In 2002, Dr. Scott Haldeman from the Department of Neurology, University of California, Irvine, and colleagues, published a study titled (5):

“Unpredictability of cerebrovascular ischemia associated with cervical spine manipulation therapy: a review of sixty-four cases after cervical spine manipulation”

The study, published in Spine, was a retrospective review of 64 medicolegal records describing cerebrovascular ischemia after cervical spine manipulation. The authors note, that up to 2002, only about “117 cases of post-manipulation cerebrovascular ischemia have 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.”

In 2008, Dr. David Cassidy and colleagues published the most comprehensive study to date pertaining to the risk of vertebral artery dissection as related to chiropractic cervical spine manipulation (6). The article was published in Spine, and titled:

“Risk of Vertebrobasilar Stroke and Chiropractic Care:

Results of a Population-Based Case-Control and Case-Crossover Study”

Key points from this article include:

1) “Vertebrobasilar artery stroke is a rare event in the population.”

2) “We found no evidence of excess risk of vertebral artery stroke associated chiropractic care.”

3) “Neck pain and headache are common symptoms of vertebral artery dissection, which commonly precedes vertebral artery stroke.”

4) “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.”

5) Most cases of vertebral arterial dissection occur spontaneously.

6) “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.”

7) “Since it is unlikely that primary care physicians cause stroke while caring for these patients, we can assume that the observed association between recent primary care physician care and vertebral artery stroke represents the background risk associated with patients seeking care for dissection-related symptoms leading to vertebral artery stroke. Because the association between chiropractic visits and vertebral artery stroke is not greater than the association between primary care physicians visits and vertebral artery stroke, there is no excess risk of vertebral artery stroke from chiropractic care.”

8) Neck manipulation “is unlikely to be a major cause” of these rare vertebral artery stroke events.

9) “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.”

10) “There is no acceptable screening procedure to identify patients with neck pain at risk of vertebral artery stroke.”

In 2004, the American Academy of Orthopedic Surgeons published a monograph titled Neck Pain (7). The second to last chapter in the monograph, chapter 7, is titled:

“Manual Therapy Including Manipulation For Acute and Chronic Neck Pain”

The editor of the monograph is Jeffery Fischgrund, MD, from the Department of Orthopaedic Surgery at William Beaumont Hospital in Royal Oaks, Michigan. This monograph has twelve respected contributors, including the authors of chapter 7, Scott Haldeman, Clinical Professor of Neurology at the University of California, Irvine, and Eric Hurwitz, Associate Professor of Epidemiology at the University of California, Los Angeles. With respect to the safety of spinal manipulation, the authors make the following comments:

“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 form 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.”

Whiplash Trauma and Vertebral Artery Dissection

On January 1, 2011, I performed a PubMed search of the National Library of Medicine database using the words “whiplash AND vertebral artery” and 60 titles were produced. The first published study was dated in 1961.

A 1991 study reported on three cases of posttraumatic vertebral artery dissection (8). All patients were young or middle-aged (range 27 to 49 years). Pain preceded neurological symptoms from hou