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The Chiropractic Impact Report

Courtesy Of Gary G Johnson

November 2019

Neck Manipulation Facts

Those who are politically engaged probably recall the last presidential debate between Donald Trump and Hillary Clinton. It occurred in Las Vegas on October 19, 2016. It was an event that under normal circumstances would have dominated the following day’s news. However, headlines in all news platforms led with a different story: A young former Playboy model had died from a stroke, and the media was attributing her injury to neck manipulation. Rebuttals to this manipulation/stroke claim were a combination of both offense and defense. An edited version of one such rebuttal is presented here:

Earlier this year the British Medical Journal published a study noting that medical errors in hospitals kill 251,000 Americans yearly (the upper range was 440,000). Assuming that medical error deaths outside of the hospital (extended care facilities, nursing homes, at home, etc.) results in an equal number of deaths, an estimated total number of yearly medical error deaths would be about 502,000. [1]

Some years back, the Journal of the American Medical Association published a study indicating that in the hospital, taking the correct drug for the correct diagnosis in the correct dosage resulted in the death of 106,000 Americans per year (the upper range was 137,000). These are considered non-error deaths as the drug, diagnosis, and dosage were all correct. The article notes that this number constitutes the 4th to 6th leading cause of yearly death in the US. Again, assuming that a similar number of deaths occur from taking the correct drug in the correct dose for the correct problem outside of the hospital setting (extended care facilities, nursing homes, at home, etc.), the number of yearly non-error deaths from medical care would be approximately 212,000. [2]

Adding the error deaths and the non-error deaths from medical care would total approximately 714,000 yearly.

Interestingly, from the Journal of the American Medical Association article, 2,216,000 Americans suffer serious adverse reactions from correctly taken drugs in the hospital yearly, but don’t die. The authors defined a serious adverse reaction as one that requires a hospital stay to recover and/or an event that resulted in a lifelong disability. [2]

In comparison, chiropractic is exceedingly safe. There are about 70,000 practicing chiropractors in the United States, and over 10,000 in California. In a typical year, chiropractic healthcare results in no deaths, and when one is alleged, it tends to make headline news. There are studies comparing chiropractic to the best pain drugs for chronic neck and/or back pain, published in the best journals, concluding that chiropractic is better than 5 times more effective than drugs; the chiropractic care had zero adverse events, while those taking the drugs had more adverse events that were benefited. [3] One of the drugs in that study was Vioxx. Vioxx was only on the market for 5 years, from 1999 to 2004. It was pulled off the market after is was realized that it was responsible for more American deaths in those 5 years (about 60,000) than the Vietnam war killed in 10 years (about 58,000).

Another example is the regular consumption of non-steroidal anti-inflammatory drugs (NSAIDs) for pain relief. Researchers from Stanford’s Medical School published an article in the world’s most prestigious medical journal, the New England Journal of Medicine, indicating that the taking of prescription NSAIDs resulted in fatal gastrointestinal bleeding 16,500 times (people) yearly, making that the 15th leading cause of yearly death in the US. [4] These same drugs are linked to increased risk of Alzheimer’s disease, deep vein thrombosis, end stage renal disease, liver damage, hearing loss, atrial fibrillation, erectile dysfunction, and more.

The young lady who is alleged to have died following a chiropractic adjustment is problematic on multiple fronts. The press release on her death mentions 2 different arteries, the carotid and the vertebral artery. Chiropractic spinal adjusting has never been linked to injury to the carotid artery. Which artery was it?

It is documented that when both the professional and lay press ascribe a manipulative injury to the vertebral artery that they apply the words “chiropractic” and “manipulation” as being synonymous; they are not. Many people “manipulate” and yet they are not chiropractors. Published studies have documented neck manipulations by lay people (barber, masseuse, hair dresser, kung fu instructor, untrained family member, etc.), resulting in vertebral artery injury, and attributing the injury to “chiropractic manipulation” when in fact it was not. [5, 6, 7] Only one type of adjustment has the potential to injure the vertebral artery, and trained-licensed chiropractors are taught not to perform that maneuver; a lay manipulator is not trained and hence would be associated with an increased risk of injury. Who did the manipulation in the case? Was it a chiropractor or a lay untrained manipulator being called a chiropractor by the press?

Recent studies, published in the best journals, have attempted to quantify the risk of a vertebral artery injury as a consequence of a chiropractic neck adjustment. One such study was published this year from researchers at John Hopkins’s Medical School. [8] These studies are suggesting that there is no risk. In contrast, they are suggesting that it appears that the patient is having a post-injury or spontaneous vertebral artery dissection, causing symptoms that bring them to a chiropractic office, and that the chiropractic adjustment has nothing to do with it. Ironically, one study, in the best medical journal, suggested that being adjusted by a chiropractor actually reduced the chances of the dissection progressing to a stroke as compared to those that had similar pathophysiology and symptoms and went to a medical doctor [9]; importantly, that study included 109 million-person years of follow-up to make their conclusions. Another study from last year with a similar conclusion evaluated about 39 million people; the point is that these are the best and biggest studies on the topic, and they are concluding that there is no stroke risk from a properly delivered chiropractic adjustment. [10] It is more probable that the injury that brought the young lady to the chiropractor’s office was responsible for her artery injury than anything the chiropractor did to try and help her (if in fact it was a chiropractor).

Even if these studies are incorrect and there is a stroke risk from a chiropractic adjustment, it is so rare that the incidence cannot be quantified. Good studies have suggested that risk might be 1 in every 3 million adjustments, which would mean that a typical chiropractor would have to be in clinical practice for literally hundreds of years to statistically be associated with a single such event, and the majority of chiropractors will never see such an event. Even so, modern chiropractors are trained to recognize the signs and symptoms of a spontaneous or traumatic vertebral artery dissection walking into their office and are educated that such a presentation is an emergency and the patient should be referred to the hospital emergency room. My partner has made 2 such referrals in the past 13 years, to the amazement of the hospital personnel and a credit to her education and experience.

Every incidence of driving one’s car is more dangerous than seeing a chiropractor.


In the first nine months of this year (2019), three new studies from prestigious medical journals have added to the understanding and statistics of the risks of a cervical artery injury (including the vertebral artery) from cervical spinal manipulation. They are reviewed here:


The first reviewed study was published in March in the journal Annals of Medicine and titled (11):

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

The authors are from the Head and Neck Research Group, Akershus University Hospital, University of Oslo, Norway. This study has 93 references. These authors note that cervical spine mobilization and/or manipulation have been suspected to be able to trigger cervical artery dissection. However, these assumptions are based on case studies which are unable to establish direct causality. The controversy relates to the chicken and the egg discussion, i.e. whether the cervical artery dissection (symptoms lead the patient to seek cervical manual-therapy or whether the cervical manual-therapy provoked cervical artery dissection.) The authors note that the controversy is a nearly impossible causality hypothesis. The authors note that cervical artery dissection is primarily thought to occur spontaneously, but that it may also be related to physical trauma to the neck. The neck positions that are thought to be most at risk are a coupling of “hyperextension and rotation.” The authors reiterate that cervical artery dissection is very rare, and that manipulation induced cervical artery dissection is extremely rare. They note that conducting sufficiently powered clinical manual-therapy randomized controlled trials to evaluate causality is nearly impossible. Their best estimate is that cervical artery dissection may be as few as 1 per 8.1 million chiropractic office visits and 1 per 5.9 million cervical manipulations by practicing chiropractors. The authors believe that the cervical artery most vulnerable to abnormal stresses is the vertebral artery. They state:

“The vertebral artery is thought to be most susceptible to injury due to extreme rotatory head movements, especially in the transverse foramen in the first cervical vertebrae, as the vertebral artery abruptly transitions from a vertical path to a horizontal orientation.”

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

Key comments from these authors in this comprehensive review include:

“The lack of established causality relates to the chicken and egg discussion, i.e. whether the cervical artery dissection symptoms lead the patient to seek cervical spinal manipulative therapy or whether the cervical spinal manipulative therapy provokes cervical artery dissection along with the non- cervical artery dissection presenting headache and/or neck complaint.”

“Several extensive cohort studies and meta-analyses have found no excess risk of cervical artery dissection resulting in secondary ischaemic stroke for chiropractic spinal manipulative therapy compared to primary care follow-up.”

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

“There is no firm scientific basis for direct causality between cervical SMT and cervical artery dissection.”

“No serious adverse events were reported in a large prospective national survey conducted in the UK that assessed all adverse events in 28,807 chiropractic treatment consultations, which included 50,276 cervical spine manipulations.”

Manual therapists, including chiropractors are taught to perform pre-manipulation provocative vertebral artery assessment testing in order to ensure that such manipulation is “safe” for the patient. However, over the last fifteen years, there has been criticism of these vertebral artery tests because of an excessive incidence of both false positives and false negatives. These author state:

“There is no sufficient evidence to support cervical vertebral artery tests to identify patients with a higher risk, and the validity and reliability of these tests are low.”

These authors end their study with a discussion that advises that if a patient has signs and/or symptoms or other warning indications of a cervical artery vascular compromise, that it is best to refer the patient for a more detailed medical vascular evaluation. Chiropractors are so taught and concur.


The second study on this topic this year was published in May in the journal BMJ Open and titled (12):

Effect of Cervical Manipulation on Vertebral Artery and Cerebral Haemodynamics in Patients with Chronic Neck Pain: A Crossover Randomised Controlled Trial

The authors are from Canadian Memorial Chiropractic College, the University of Ontario Institute of Technology, McMaster University Faculty of Engineering, and the University of Toronto. This study cites 67 references. This study took place in the Imaging Research Centre at St. Joseph’s Hospital in Hamilton, Ontario, Canada. These authors aimed to determine whether cervical spine manipulation is associated with meaningful changes in vertebral artery and cerebrovascular hemodynamics measured with 3-Telsa MRI compared with neutral neck position and maximum neck rotation in patients with chronic neck pain. Twenty subjects aged 23–66 years were enrolled in the study. The cervical manipulation procedure was a supine high velocity, low amplitude impulse, with targeted contact at C1–C2 on the side of most discomfort as elicited on palpation. The subject’s head was in combined axial rotation, flexion and lateral flexion postures. The authors note that this is the first study to measure cerebral blood flow, vertebral artery blood flow and velocity in patients undergoing neck manipulation for neck pain. The authors note that patients with neck pain frequently consult chiropractors and manipulation of the cervical spine is commonly performed for symptomatic relief. This, coupled with the fact that vertebrobasilar artery stroke secondary to vertebral artery dissection is so rare, that “very little is known about the risk factors for vertebrobasilar artery stroke.” Key findings and comments from these authors include:

“We found no significant changes within the cerebral haemodynamics following cervical manipulation or maximal neck rotation.”

“The changes observed were found to not be clinically meaningful and suggests that cervical manipulation may not increase the risk of cerebrovascular events through a haemodynamic mechanism.”

“When compared with neutral neck position, maximal neck rotation and cervical manipulation did not significantly alter cerebral perfusion within the posterior cerebrum or cerebellum.” [This is the territory supplied by the vertebral arteries].

“Our work is the first to show that cervical manipulation does not result in brain perfusion changes compared with a neutral neck position or maximal neck rotation.”

“None of the participants during any of the experimental procedures reported, or were observed by the investigators, to have any signs or symptoms of neurological compromise.”

“No major adverse events were reported.”

“Together with previous work, our results support the position that the association between cervical manipulation and stroke is due to protopathic bias.” [Protopathic Bias is when a treatment for the symptoms of a disease or injury appears to cause the outcome].

“In conclusion, we found no significant change in blood flow in the posterior cerebrum or cerebellum in chronic neck pain participants after maximum head rotation and cervical manipulation.”

“Our study adds to a growing body of knowledge regarding the impact of head position and cervical manipulation on vascular and neural activity in patients with neck pain.”

“Our study does not support the hypothesis that neck manipulation or neck rotation are associated with vasospasm of the vertebral artery.”

In an interesting irony, the authors suggest that their research showed that physiological head/neck rotation was more likely to alter cervical and cranial blood flow than the manipulative thrust. They note:

“Given the changes in vertebral artery haemodynamics are more pronounced following maximal head rotation compared with cervical manipulation, specifically in contralateral flow, the changes may be the result of the head turning rather than the effect of the thrust associated with cervical manipulation.”

“This assumption is supported by those who suggest that cervical manipulation imposes less stretch to the vertebral artery than the turning of the head.”

This unique study adds to the evidence that cervical manipulation is quite safe and unlikely to cause vertebral artery injury. It should be emphasized that, chiropractors are trained to not deliver manipulation thrust to C1-C2 in maximum rotation and extension, and if cranial vascular signs or symptoms occur prior, during, or after any patient contact, that additional evaluation and perhaps referral may be in the patient’s interest.


The third study on this topic this year was published in July (as an epub) in the Journal of Orthopaedic & Sports Physical Therapy and titled (13):

Effects of Head and Neck Positions on Blood Flow in the Vertebral, Internal Carotid and Intracranial Arteries: A Systematic Review

The authors are from Hanze University, Groningen, The Netherlands; University of Groningen, The Netherlands; Rotterdam University, Rotterdam, The Netherlands; HAN University of Applied Sciences, Nijmegen, The Netherlands; University of Nottingham, UK. This study cites 59 references. This study is a systematic review of the literature that initially identified 1,453 studies and used 31 that met their inclusion criteria. In total, they used studies involved 2,254 participants. The mean age of these participants was 55 years ranging from 18–98 years. The objective was to investigate the effects of cranio-cervical positions and movements (manual therapy interventions) on hemodynamic changes (blood flow velocity and/or volume) of cervical and cranio-cervical arteries, including the vertebral arteries. Blood flow was tested in multiple patient positions (supine, sitting, prone), but for the vertebral artery, maximum rotation and the combination of maximum rotation and extension were the positions tested most frequently. Manual therapy is used for the management of people with head and neck pain. Manual therapy is performed utilizing various positions and movements of the craniocervical region. Cervical manual therapy interventions have “rarely been associated with adverse events,” but the exact incidence rates of such adverse events are unknown. One of the most frequently claimed adverse events following cervical treatment techniques is arterial dissection. Yet, “studies have been unable to identify specific variables which relates to the increase or mediation of risk for adverse events.” A commonly described symptom of cervical arterial dysfunction is neck or head pain. These patients may seek assistance from a manipulative therapist for evaluation and treatment for relief of pain and improvement of function. It is plausible that a cervical arterial dysfunction is not an adverse event of the treatment itself, but exists in situ prior to treatment. Key findings and comments from these authors in this systemic review include:

Most of the studies in this review “mentioned no significant hemodynamic changes during maximal rotation.”

“Three studies focused on high velocity thrust positioning and movement, all reported no hemodynamic changes.”

“The positions and movements utilized in high velocity thrust techniques do not seem to alter blood flow.”

“Based on these data it is unlikely that head and neck movement alone, even if forceful, could mechanistically explain the aetiology of adverse events which have conventionally been purported to be related to therapeutic interventions.”

“Conventional thought within the domain of manual therapy has been that rapid, forceful interventions such as high velocity thrust techniques are considered to constitute a higher risk for neuro-vascular events resulting from cervical arterial compromise. However, we found that studies which focused specially on high velocity thrust reported no hemodynamic changes.”

“The synthesized data suggest that in the majority of people most positions and movements of the cranio-cervical region do not have an effect on blood flow.”

“The data synthesized from 31 experimental and quasi-experimental studies suggest that in most people cranio-cervical positions and movements had no effect on blood flow.”

“A clinical implication from this review is that the relationship between cranio-cervical movement and alterations in blood flow does not seem to be as obvious as previous data suggested.”

This study “suggests that adverse events related to cervical spine interventions might be the result of something other than the therapeutic positioning or movement of the head and neck.”

“Conclusion: Our results suggest that in most people, healthy as well as patients with vascular pathologies, cranio-cervical positions do not alter cervical blood flow. This includes vascular test positions, pre-manipulative positions and manipulations.”

“A key clinical implication from this review is that the relationship between cranio-cervical movement and blood flow does not seem to be as previously suggested.”

These authors also point out that pre-manipulative vascular integrity tests (functional positional tests) are unable to establish a relationship between vertebral artery blood flow changes and symptom reproduction. “Therefore, the rationale and value of the tests should be questioned.” These authors end their study with a discussion claiming that there may be small sub-groups of the population with underlying arterial pathology where the small hemodynamic changes may be sufficient to induce or exacerbate a neuro-vascular compromise. They suggest that it might be wise to initially use treatment techniques with less than 45 degrees of cervical rotation.


Taken together, these studies support these points:

  • Cervical spine vascular accidents occur spontaneously. Linking cervical vascular accidents to cervical manipulation may be nonexistent at best and at worse overstated in prior publications.
  • Cervical spine vascular accidents occur so rarely that it is essentially impossible to study their occurrence and mechanisms.
  • The available evidence indicates that that cervical adjusting (specific manipulation) is extremely safe, especially in the hands of trained professionals, like chiropractors.
  • Some patients may have elevated risk factors for cervical spine vascular injury, and these risk factors are essentially impossible to ascertain.
  • Patients who are suffering from cervical artery compromise often present to chiropractic offices for treatment.
  • Pre-manipulation positional cervical artery testing is probably not valid.
  • It may be prudent to not rotate the head/neck in excess of 45 degrees when initially manipulating the cervical spine.
  • It is probably ill advised to combine C1-C2 rotation/extension/thrust manipulation.


  1. Makary MA, Daniel M; Medical Error: The Third Leading Cause of Death in the United States; British Medical Journal; May 3, 2016; Vol. 353; i2139.
  2. Lazarou J, Pomeranz BH, Corey PN; Incidence of Adverse Drug Reactions in Hospitalized Patients: A Meta-analysis of Prospective Studies; Journal of the American Medical Association; Vol. 279; No. 15; April 15, 1998; pp. 1200-1205.
  3. Giles GFL, Muller R; Chronic Spinal Pain: A Randomized Clinical Trial Comparing Medication, Acupuncture, and Spinal Manipulation; Spine; July 15, 2003; Vol. 28; No. 14; pp. 1490-1502.
  4. Wolfe MM, Lichtenstein DL, Singh G; Gastrointestinal Toxicity of Nonsteroidal Anti-inflammatory Drugs; The New England Journal of Medicine; June 17, 1999; Vol. 340; No. 24; pp. 1888-1899.
  5. Terrett AG; Misuse of the literature by medical authors in discussing spinal manipulative therapy injury; Journal of Manipulative and Physiological Therapeutics; May 1995; Vol. 18; No. 4; pp. 203-210.
  6. Weban A, Beck J, Raabe A, Dettmann E. Seifert V; Misuse of the terms chiropractic and chiropractor; J Neurol Neurosurg Psychiatry; May 2004; Vol. 75; No. 5; p. 794.
  7. Weban A; Inappropriate use of the title ‘chiropractor’ and term ‘chiropractic manipulation’ in the peer-reviewed biomedical literature; Chiropractic and Osteopathy; August 2006; Vol. 22; Vol. 14; p. 16.
  8. Church EW, Sieg EP, Zalatimo O, Hussain NS, Glantz M, Harbaugh RE; Systematic Review and Meta-analysis of Chiropractic Care and Cervical Artery Dissection: No Evidence for Causation; Cureus; February 16, 2016; Vol. 8; No. 2; e498.
  9. Cassidy, J David DC, PhD; Boyle, Eleanor PhD; Côté, Pierre DC, PhD; He, Yaohua MD, PhD; Hogg-Johnson, Sheilah PhD; Silver, Frank L. MD; Bondy, Susan J. PhD; Risk of Vertebrobasilar Stroke and Chiropractic Care: Results of a Population-Based Case-Control and Case-Crossover Study; Spine; Vol. 33(4S); February 15, 2008; pp. S176-S183.
  10. Kosloff TM, Elton D, Tao J, Wade M Bannister WM; Chiropractic Care and the Risk of Vertebrobasilar Stroke: Results of a Case–control Study in U.S. Commercial and Medicare Advantage Populations; Chiropractic & Manual Therapies 2015; Vol. 23; No. 19; pp. 1-10.
  11. Chaibi A, Russell MJ; A Risk–benefit Assessment Strategy to Exclude Cervical Artery Dissection in Spinal Manual Therapy: A Comprehensive Review; Annals of Medicine; March, 2019; Vol. 19; pp. 1-10.
  12. Moser N, Mior S, Noseworthy M, Cote P, Wells G, Behr M, Triano J; Effect of Cervical Manipulation on Vertebral Artery and Cerebral Haemodynamics in Patients with Chronic Neck Pain: A Crossover Randomised Controlled Trial; BMJ Open; May 28, 2019; Vol. 9; No. 5; pp. e025219.
  13. Kranenburg R, Tyer R, Schmitt M, Luijckx GJ, van der Schans C, Hutting N, Kerry R; Effects of Head and Neck Positions on Blood Flow in the Vertebral, Internal Carotid and Intracranial Arteries: A Systematic Review; Journal of Orthopaedic & Sports Physical Therapy; July 2019 [epub].

“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.”