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The Evidence-Informed Chiropractor


The Evidence Regarding the Risks of Chiropractic Care



Manipulation and VBA Stroke in the U.S.

A recent publication again brings to light the controversial topic of vertebrobasilar stroke and chiropractic manipulation. This newest attempt to clarify any association between manipulation and VBA stroke was conducted in the U.S. and is the largest study to date.


The purpose of this 2015 U.S. case-control study was:

  • To replicate the case–control epidemiological design published by Cassidy, et al.
  • Study the association between chiropractic care and VBA stroke
  • And compare the association between recent PCP care and VBA stroke in samples of the U.S. commercial and Medicare Advantage (MA) populations

The patient population studied and sampled was from the Membership in a Commercial or MA Health Plan

  • Members had to be either residing or working in a region where health care coverage was offered
  • And must have Medicare Part A and Part B to join a MA plan
  • 49 states were represented. The Only state not represented was North Dakota
  • There were over 35,million unique commercial
    members and just over 3 million unique MA members

This study is the largest case– control study to investigate the association between chiropractic manipulation and VBA stroke with a total of 1,829 VBA stroke cases

The Prevalence of VBA Stroke was very low In the Commercial population

It was 0.021%. And for the Medicare Advantage population it was 0.0032%


The data indicates that there is no association between chiropractic visits and VBA stroke regardless of age stratification (< 45 or > 45 y/o) in either the commercial or MA populations


There was a significant association between PCP visits and VBA stroke regardless of the length of the hazard period


Link to Featured Publication

2015 Chiropractic and Manual Therapies Article

Manipulation and VBA Stroke in a U.S. Population


Spinal Manipulation and Adverse Events in Seniors: Two Medicare Beneficiary Studies

Recently, two studies comparing risk association to manipulation published in 2015 was based on all Medicare beneficiaries. One focuses on stroke related to chiropractic visits and the other is broader looking at all serious adverse events. This is the first large-scale data study to address issues specifically with the senior population. The concern is that the understanding of the results will be confused with a cause and effect relationship. Any relationship to adverse events in these two studies is likely coincidental to the time frame of the "hazard period" for both DCs and MDs.

All beneficiaries covered under Medicare B, aged 66-99 with at least one allowed Medicare B claim in 2007 for an office visit to either a chiropractor or PCP, with an associated ICD-9 diagnosis code for a neuromusculoskeletal problem

Chiropractic Cohort Compared to Primary Care Cohort within seven days of an office visit . . .

  • 28 per 10,000 in the chiropractic cohort
  • 36 per 10,000 in the primary care cohort

Cumulative probability of injury was lower in the chiropractic cohort as compared to the primary care cohort (1 vs. 21 injury incidents per 100,000)

Adjusting for differences in patient characteristics, risk of injury in the chiropractic cohort was 76% lower compared to the primary care cohort (hazard ratio 0.24; 95% CI 0.23-0.25)

In the Medicare study on stroke related to cervical spine pain, the specific incidence of VBS was too small to report.

2014 Spine Study on Medicare Patients and Adverse Events with Manipulation

2015 JMPT Medicare Study on Stroke



The 2014 AHA Stroke Report

The American Heart Association with the American Stroke Association published recommendations to healthcare providers about cervical artery stroke in relation to cervical manipulation. Their conclusions leave much to be desired. Their interpretation of the literature seems to ignore the facts and rest largely on a biased concern.


·    Cervical dissection accounts for only 2% of all ischemic strokes, but accounts for 8% to 25% of stroke in patients <45 years of age


·    Internal carotid artery (ICA) dissection has an annual incidence of 2.5 to 3 per 100 000 patients


·    Vertebral artery (V A) dissection (V AD) has an annual incidence of 1 to 1.5 per 100 000 people


·    Aberrations of dermal collagen fibrils and elastic fibers have been reported in ≈50% of patients with spontaneous CDs


·    The reported prevalence of trivial trauma is estimated to be between 12% - 34% in which cervical manipulation is combined with non-manipulative events

Basic science evidence AGIANST CMT as a potential cause . . .

·         Evidence that blood flow is not decreased with rotation


·         Evidence that the strain forces with SMT do not exceed failure rates of arteries


·         Evidence that strain forces with SMT are no greater than normal activities

Take-Home Points from Cassidy et al. Study:

  •  In those under 45 years old, individuals were three times more likely to see a chiropractor OR a primary care practitioner (PCP) before their stroke compared to controls
  •  There was no increased association between VB stroke and chiropractic visits in those older than age 45
  •  There was an association between VB stroke and patients of all ages visiting a PCP prior to stroke
  •  Cause was not studied only the association between stroke, time, and a visit to either a chiropractor or medical doctor

The 2014 VA Study on Vertebral Artery Stroke Obvious limitations

· Exposure to SMT for individual patients was not available in the VA database and was not collected

  • The VA population was 90% male
  • Previous Canadian studies investigated a broader demographic population over a longer period using different coding and administrative processes
  • The researchers went as far as creating hypothesized rates of VBA rates based on time after exposure to a non-existent chiropractic visit (manipulation)
  • Given the authors want to attribute atherosclerotic (emboli) causes for posterior circulation strokes, it must also be allowed for chiropractors given the hazard period was ONE MONTH after a visit
  • If patients with cardiovascular risk factors are at higher risk and, therefore, the cause of the increased association with MDs, why is it that in the Cassidy et al. study: hypertension, heart disease, and high cholesterol were 2-3 times higher in the control group (those who did not have a stroke?

VAI Incidence with Cervical Surgery . . .

• Overall the incidence was 0.07% (7/10,000)

• The incidence was higher for those who had performed 300 or less procedures 0.33% (3/1,000)

• For those with more than 300 procedures the incidence was 0.06% (6/10,000)

• Are there measures that can be taken to decrease VAI for cervical spine surgeries?

• Patients should be warned of the statistics regarding their procedure

• Patients should be made aware of the significantly increased risk when being operated on by a less experienced surgeon

• Patients scheduled for upper cervical procedures should consider requiring a CT with contrast be performed prior to that surgery to identify anomalous vertebral artery locations

Summary of Evidence

• The rational, evidence-based approach is to simply state that CMT is a safe procedure with extremely rare association to stroke also found with visits to medical doctors, and that it has never been directly linked to cause and effect.

• In the vast majority of cases, it is likely that the patient is in the process of dissection complaining of severe neck or headache pain


The 2014 AHA Stroke Article

The 2014 Systematic Review of Internal Carotid Artery Dissection in JMPT




A body of evidence suggests that chiropractic care is generally safe; however, as with any form of treatment, some risk may be involved. Listed below are summaries of both common and rare side-effects/complications reported to be associated with chiropractic care:


Common (1, 2)

  • Reactions most commonly reported are local soreness/discomfort (53%), headaches (12%), tiredness (11%), radiating discomfort (10%), dizziness, the vast majority of which resolve within 48 hours

Rare (3, 4)

  • Fractures or joint injuries in isolated cases with underlying physical defects, deformities or pathologies
  • Burns due to some physiotherapy procedures
  • Disc herniation
  • Cauda equina Syndrome (2) (1 case per 100 million adjustments)
  • Vertebrobasilar artery (VBA) stroke (1 case per 400,000 to 1 million cervical spine adjustments [manipulations]).

A similar level of association to vertebrobasilar stroke is found for patients under the age of 45 when consulting with a medical doctor; for those older than age 45, the association to vertebrobasilar stroke is higher when seeing a medical doctor than a chiropractic doctor.

Why is the association similar for visiting an M.D. or chiropractor? Because manipulation is not the cause.


Remember this is an association; not a cause-and-effect relationship. Patients who are in the process of dissection (tearing of the inner layer of the artery) are often experiencing headache or neck pain. They then seek attention from their M.D. or chiropractor while in the process of having a stroke. Given M.D.s are not likely to perform manipulation, manipulation is incorrectly assumed as the mechanical cause when patients are seen by a chiropractor. Given that the association to VBA stroke and seeing an M.D. is equal to or greater than that associated with seeing a chiropractor, the only logical explanation is that the dissection is already in progress creating symptoms that cause the patient to seek help.


There is no in-office test that can determine if a patient is at risk for dissection. The only clue for the doctor is a headache that is "first or worse" meaning a headache that is "new" to the patient and the worst headache they have experienced.


Patients are directed to please indicate to your doctor if you have headache or neck pain that is the worst you have ever felt(3)


1. Thiel HW, Bolton JE, Docherty S, Portlock JC. Safety of chiropractic manipulation of the cervical spine: a prospective national survey. Spine. Oct 1 2007;32(21):2375-2378; discussion 2379.
2. Rubinstein SM, Leboeuf-Yde C, Knol DL, de Koekkoek TE, Pfeifle CE, van Tulder MW. The benefits outweigh the risks for patients undergoing chiropractic care for neck pain: a prospective, multicenter, cohort study. J Manipulative Physiol Ther. Jul-Aug 2007;30(6):408-418.
3. Cassidy JD, Boyle E, Cote P, et al. Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case-control and case-crossover study. Spine. Feb 15 2008;33(4 Suppl):S176-183.
4. Boyle E, Cote P, Grier AR, Cassidy JD. Examining vertebrobasilar artery stroke in two Canadian provinces. Spine. Feb 15 2008;33(4 Suppl):S170-175.

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