Spinal Manipulation and
Vascular Risk Safety:

The Safety Evidence Continues to Grow

Both health care providers and lay people may manipulate the spine. The health care provider group most likely to employ spinal manipulation is chiropractic. A recent (2017) in-depth analysis indicates that there are approximately 70,000 practicing chiropractors in the United States, the majority of whom use spinal manipulation in their clinical practice (1). There are eighteen government accredited chiropractic colleges located throughout the United States. Many of them have achieved university status, granting academic degrees in addition to chiropractic degrees (DC degree).

The lay press and occasionally peer-reviewed journals claim that cervical spine manipulation may cause injury to a cervical artery. This claim is exceptionally controversial because proof of such an occurrence is impossible and the alleged incidence is so incredibly rare that definitive conclusions are also impossible.

The most recent credible evidence (March 2019) estimates the claim of cervical artery injury to be as few as 1 per 8.1 million chiropractic office visits and 1 per 5.9 million cervical manipulations by practicing chiropractors (2). Assuming that a typical chiropractor has 20 patient visits per day, 100 patient visits per week, 5,000 patient visits per year, and a 40-year career, this would total approximately 200,000 patient visits. Such a chiropractor would have to be in clinical practice, at that volume, for 1,200 years before statistically seeing a single alleged vascular injury event.

Although cervical artery dissection primarily occurs spontaneously, physical trauma to the neck, especially traumas involving hyperextension and rotation, has been suspected to trigger them. This is especially noted with whiplash-type injury mechanisms (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13).

Despite this incredibly low incidence of risk, students in chiropractic college are taught about such risks out of an abundance of caution; chiropractors are licensed health care professionals. The cervical arteries at risk are the internal carotid artery and the vertebral artery.

The artery that has the greatest risk for injury is the vertebral artery. This is because the vertebral artery ascends in the cervical vertebrae, in a hole called the foramen transversarium.

The atlas-axis (C1-C2) vertebral articulation of the cervical spine is mechanically unique. It is designed for the function of rotational motion. Theoretically, such rotation places the vertebral artery at increased risk of tractional stress, increasing the potential for injury. Students in chiropractic college are taught not to apply a rotational manipulative thrust of C1 on C2. Furthermore, biomechanical studies indicate that the vertebral artery will experience additional tractional stress if the upper cervical spine is in extension. Chiropractic college students are taught not to use the combination of C1—C2 rotation—extension—thrust manipulations (adjustments).

Cervical Artery Injury 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 breaking free and traveling distal from 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.

The signs and symptoms that would warn of a possible vertebral artery dissection with ischemia are summarized as the 5 Ds And the 3 Ns (14):

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)
Nystagmus
Numbness (hemianesthesia)

A history that would warn of a possible acute 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 (14).

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 (14):

Childbirth
By Surgeon or Anesthetist During Surgery
Calisthenics, Athletics, Fitness Exercise
Yoga
Overhead Work, Painting a Wall
Hanging Out the Wash
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
Archery
Sneezing/Nose Blowing/Coughing
Wrestling
Emergency Resuscitation
Star Gazing, Watching Aircraft
Sleeping Position
Swimming
Break Dancing
Football
Beauty Parlor Stroke, Sitting in a Barber’s Chair
Tai Chi
Sexual Intercourse

Peer-reviewed journals that ascribe cervical artery dissections to chiropractic manipulation have been proven to be incorrect (15). 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, despite knowing that it was not the case. The list of discovered manipulators included:

A Blind Masseur
An Indian Barber
A Wife
A Kung-Fu Practitioner
Self-Manipulation
Medical Doctor
Osteopath
Naturopath
Physical Therapist

Several other peer-reviewed studies have confirmed a similar misrepresentation of chiropractic in the literature (16, 17).

The Major Controversy: Correlation/Association v. Causation

These questions are perpetually debated:

• Did the manipulation cause an artery injury? If yes, it is causation.
• Did the patient already have an artery injury that produced symptoms and the patient subsequently went to a provider that manipulates to treat the symptoms? In other words, the manipulation did not cause the injury because it pre-existed. If yes, it is correlation/association, and NOT causation.

••••••••••

Selective Review of Credible Publications

In 2002, Dr. Scott Haldeman from the Department of Neurology, University of California, Irvine, and colleagues, published a study in the journal Spine titled (18):

Unpredictability of Cerebrovascular Ischemia Associated
with Cervical Spine Manipulation Therapy:
A Review of Sixty-four Cases After Cervical Spine Manipulation

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 a comprehensive study pertaining to the risk of vertebral artery dissection as related to chiropractic cervical spine manipulation. The article was published in Spine, and titled (19):

Risk of Vertebrobasilar Stroke and Chiropractic Care:
Results of a Population-Based Case-Control and Case-Crossover Study

Key points from this article include:

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

“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.”

•••••

In 2010, Dr. Donald Murphy published an article in the journal Chiropractic and Osteopathy, titled (20):

Current Understanding of the Relationship
Between Cervical Manipulation and Stroke:
What Does it Mean for the Chiropractic Profession?

In this article, Dr. Murphy states:

“The understanding of the relationship between cervical manipulative therapy (CMT) and vertebral artery dissection and stroke (VADS) has evolved considerably over the years.”

“In the beginning the relationship was seen as simple cause-effect, in which CMT was seen to cause VADS in certain susceptible individuals. This was perceived as extremely rare by chiropractic physicians, but as far more common by neurologists and others.”

“Recent evidence has clarified the relationship considerably, and suggests that the relationship is not causal, but that patients with VADS often have initial symptoms which cause them to seek care from a chiropractic physician and have a stroke some time after, independent of the chiropractic visit.”

•••••

In 2011, the Journal of Manipulative and Physiological Therapeutics published a population-based case series using administrative health care records of all Ontario, CAN, residents hospitalized with vertebral artery stroke between April 1, 1993, and March 31, 2002, titled (21):

A Population-based Case-series of Ontario Patients Who Develop a Vertebrobasilar Artery Stroke After Seeing a Chiropractor

These authors note:

“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.”

•••••

Also in 2011, The Open Neurology Journal published an editorial by Drs. Dean Smith and Gregory Cramer, titled (22):

“Spinal Manipulation is Not an Emerging Risk Factor for Stroke Nor is it Major Head/Neck Trauma. Don’t Just Read the Abstract!”

Dean L. Smith is Clinical Faculty, Department of Kinesiology and Health, Miami University, Oxford, Ohio, and Gregory D. Cramer is Professor and Dean of Research, National University of Health Sciences, Lombard, Illinois. Their editorial includes:

We would like to address two points in this letter:

1) The current best-evidence indicates no causal relationship between spinal manipulation (‘chiropractic maneuver’ in the paper) and vertebrobasilar artery (VBA) stroke.

2) Spinal manipulation or ‘chiropractic maneuvers’ are not major head/neck trauma as suggested in the abstract of this article.

“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.”

“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.”

•••••

In 2012, Dr. Walter Herzog and colleagues published a study in the Journal of Electromyography and Kinesiology titled (23):

Vertebral Artery Strains During High-speed, Low Amplitude
Cervical Spinal Manipulation

This study presents the first ever data on the mechanics between C1/C2 during cervical SMT performed by chiropractic clinicians. The authors compared the results of human VA strains during high-speed, low-amplitude SMTs administered by qualified chiropractic clinicians and compared them to the strains encountered during full range of motion (ROM) tests. They used a total of 3,034 segment strains obtained during SMTs and 2,380 segment strains obtained during full ROM testing, making this is an extensive study. The authors conclude:

“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.”

“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.”

•••••

An extensive review of the literature pertaining to the relationship between cervical spine manipulation and cervical artery dissection was published in the journal Stroke in 2014 (24). Stroke is the official journal of the American Heart Association. The title of the article is:

Cervical Arterial Dissections and Association
With Cervical Manipulative Therapy

Key points from this publication include:

• Cervical artery “dissections can be either spontaneous or traumatic.”
• “Current biomechanical evidence is insufficient to establish the claim that cervical manipulation causes cervical artery dissection.”
• “The underlying pathogenesis responsible for spontaneous cervical artery dissections is unknown.”
• The vertebral artery (VA) between C1-C2, where most of cervical spine rotation occurs, “is most susceptible to injury.”
• “Current biomechanical evidence is insufficient to establish the claim that spinal manipulation causes cervical artery dissection, including data from a canine model showing no significant changes in VA lesions before and after cervical manipulation.”
• “Because patients with VAD commonly present with neck pain, it is possible that they seek therapy for this symptom from providers, including cervical manipulation practitioners, and that the VAD occurs spontaneously, implying that the association between cervical manipulation and VAD/vertebrobasilar artery stroke is not causal.”
• There is no gold standard diagnostic test for cervical artery dissection.

•••••

In 2015, Dr. Thomas Kosloff and colleagues published a study in the journal Chiropractic & Manual Therapies titled (25):

Chiropractic Care and the Risk of Vertebrobasilar Stroke:
Results of a Case–control Study in U.S. Commercial
and Medicare Advantage Populations

The main purpose of this study was to replicate the case–control epidemiological design study published by Cassidy, et al. in 2008 (19), and to investigate the association between chiropractic care and vertebral artery stroke. The authors assessed commercially insured and Medicare Advantage (MA) health plan members in the U.S. The data set included health plan members located in 49 of 50 states (excluded North Dakota) and encompassed national health plan data for 35,726,224 commercial and 3,188,825 MA members. Hence, this study looked 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:

“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.”

•••••

In 2016, authors from the Department of Neurosurgery, Penn State Hershey Medical Center, and the Department of Neurosurgery, Johns Hopkins University School of Medicine, published a study in the journal Cureus titled (26):

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

These authors evaluated the evidence related to this topic by performing a systematic review and meta-analysis of published data on chiropractic manipulation and cervical artery dissection (CAD). They state:

“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.”  

“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.”

•••••

As noted at the beginning of this article, additional evidence has been added to the topic of cervical artery injury and cervical spine manipulation. The article was published March 2019 in the journal Annals of Medicine, and titled (2):

A Risk–benefit Assessment Strategy to Exclude Cervical Artery Dissection in Spinal Manual Therapy: A Comprehensive Review

The authors note that conducting sufficiently powered clinical manual-therapy randomized controlled trials to evaluate causality of spinal manipulation and cervical artery dissection is “nearly impossible” because “to scientifically establish the prevalence of CAD as a direct trigger of cervical mobilization and/or manipulation intervention, a prospective study would need to include 1000 manual therapists treating the cervical spine 100 times per week for 52 weeks.”

Overall, key concepts from this study include:

“There is no strong evidence in the literature that manual therapy provokes cervical artery dissection.”

“It is highly unlikely that mobilization and manipulative techniques that tend to be specific with minimal force and amplitude affect the internal carotid arteries.”

“All people execute several different head and neck movements every day, including side-to-side neck rotations that consequently stretch the VA. Fortunately, this usually does not trigger cervical artery dissection.”

“The assumption that the cervical manual-therapy intervention triggers cervical artery dissection in rare cases has been dominated by single-case reports and retrospective case series or surveys from neurologists who naturally lack substantial methodological quality to establish definitive causality.”

“The reality is, there is no firm scientific basis for direct causality between cervical spinal manipulative therapy and cervical artery dissection.”

•••••

Chiropractic students and chiropractors are extensively trained in the anatomy and biomechanics of the upper cervical spine. They are also extensively trained in the science and art of spinal adjusting (specific directional manipulation). Vertebral artery injury ascribed to chiropractic manipulation in the peer-reviewed literature is often inappropriate as the actual manipulation was done by an untrained layperson or untrained healthcare provider.

All therapeutic interventions have risk. The risk of cervical artery dissection from cervical manipulation is extremely low, and may be nonexistent. The symptoms associated with spontaneous vertebral artery dissection may bring the patient into chiropractic offices.

Despite the uncertainty of the relationship between cervical manipulation and cervical artery injury, informing each patient of the potential risk is prudent. If any of the 5 Ds And the 3 Ns are present, either before or after spinal manipulation, an appropriate referral should be made.

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“Authored by Dan Murphy, D.C.. Published by ChiroTrust® – This publication is not meant to offer treatment advice or protocols. Cited material is not necessarily the opinion of the author or publisher.”