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Healthcare Risks and Safety

The realization that trying to stay healthy can be risky became international headlines in 1994 when Harvard’s Lucian Leape, MD, indicated that medical error was responsible for 180,000 deaths per year (1, 2). Dr. Leape’s analogy was that this was “the equivalent of three jumbo-jet crashes every 2 days (2).”

Dr. Leape’s premise of “Error in Medicine” was updated earlier this year (2016), showing that the problem has not improved in the past two decades. Published in the British Medical Journal, Johns Hopkins University School of Medicine professor Martin A. Makary (MD, MPH) and research fellow Michael Daniel (medical student) produced an article titled (3):

Medical Error The Third Leading Cause of Death in the United States

In this study, Makary and Daniel analyzed the scientific literature on medical error to identify its contribution to US deaths. They note that medical error harm and deaths occur as a consequence of:

In their appraisal of the magnitude of the problem, they note:

“We calculated a mean rate of death from medical error of 251,454 a year.”

“We believe this understates the true incidence of death due to medical error because the studies cited rely on errors extractable in documented health records and include only inpatient deaths.”

“Medical error is the third biggest cause of death in the US and therefore requires greater attention.”

Importantly, Makary and Daniel note that the annual list of the most common causes of death in the United States, compiled by the Centers for Disease Control and Prevention (CDC), has a major limitation as it relies on assigning an International Classification of Disease (ICD) code to the cause of death, and ICD code does not include error. They state:

“Medical error is not included on death certificates or in rankings of cause of death.” Death certificates “have no facility for acknowledging medical error.”

“The system for measuring national vital statistics should be revised to facilitate better understanding of deaths due to medical care.”

Following the publication of this study, Makary, Daniel, and colleagues sent a letter to Dr. Thomas Frieden, Director, US Centers for Disease Control and Prevention (May 1, 2016). This letter, in part, notes:

Dear Dr. Frieden,

“We are writing this letter to respectfully ask the Centers for Disease Control and Prevention (CDC) to change the way it collects our country’s national vital health statistics each year.”

“The list of most common causes of death … has neglected to identify the third leading cause of death in the U.S.—medical error.”

“The limitation stems from a historic policy that says death certificates can only be tabulated with an ICD billing code.”

“From studies that analyzed documented health records, we calculated a pooled incidence rate of 251,454 deaths per year. If we project this quantity into the total number of deaths in the year 2013 (2,596,993 deaths), they would account for 9.7% of all deaths in the nation. This figure far surpasses the current third leading cause of death on the CDC’s most recent rank order. Moreover, the 251,454 estimate we derived from the literature is an underestimate because the studies conducted did not include outpatient deaths or deaths at home due to a medical error.”

“Causes of death not associated with an ICD code, such as human and system factors in medical care, are not captured.”

“We suggest that the CDC allow clinicians to list medical error as the cause of death, and, in the interim, the CDC should list medical error as the third most common cause of death in the U.S. after heart disease (611,105 deaths per year) and cancer (584,881 deaths per year) and replacing respiratory disease (149,205 deaths per year).”

“The ICD code book is limited in its ability to be a classification system for keeping national health vital statistics due to its inability to capture most types of medical error.”

“Reducing costly medical errors is critical towards the important goal of creating a safer, more reliable health care system. Measuring and understanding the problem is the first step.”

As noted, the 251,000 deaths from medical error underestimates the actual number because it represents only medical error deaths that occur in the hospital setting. Medical error deaths occurring in non-hospital facilities or at home are not included in the estimated number.

In addition, correctly applied medical care (medical care that is not considered to be an error), is also capable of causing death and serious adverse events. A study quantifying such non-error death and serious adverse events was published in the Journal of the American Medical Association, and titled (5):

Incidence of Adverse Drug Reactions in Hospitalized Patients A Meta-analysis of Prospective Studies

The objective of this study was to estimate the incidence of serious and fatal adverse drug reactions (ADR) in hospital patients. Serious ADRs were defined as those that required hospitalization, were permanently disabling, or resulted in death. The authors performed a meta-analysis of 39 prospective studies done in the United States over a period of 32 years on the incidences of Adverse Drug Reactions (ADRs). The goal of this study was to “estimate injuries incurred by drugs that were properly prescribed and administered.” If the event was determined to be a “Possible ADRs” it was excluded from this study. The authors noted:

“We estimated that in 1994 overall 2,216,000 (1,721,000-2,711,000) hospitalized patients had serious ADRs and 106,000 (76,000-137,000) had fatal ADRs, making these reactions between the fourth and sixth leading cause of death.”

“We have found that serious ADRs are frequent and more so than generally recognized. Fatal ADRs appear to be between the fourth and sixth leading cause of death. Their incidence has remained stable over the last 30 years.”

“It is important to note that we have taken a conservative approach, and this keeps the ADR estimates low by excluding errors in administration, overdose, drug abuse, therapeutic failures, and possible ADRs. Hence, we are probably not overestimating the incidence of ADRs.”

This study on ADRs excluded medicatio “to show that there are a large number of serious ADRs even when the drugs are properly prescribed and administered.”

“The incidence of serious and fatal ADRs in US hospitals was found to be extremely high.”

Once again, these “fallout” numbers result in an underestimation of the magnitude of the global problem because the authors only assessed death and serious averse events in the hospital setting. Similar deaths and serious adverse events outside of the hospital setting and/or in the home would not be included in the author’s numbers.

These “fallout” deaths and serious adverse events from taking the proper drug in the proper dose for the correct diagnosis represent a different patient population than those who die as a consequence of hospital error, and as such the numbers would be additive in estimating medical care induced death (251,000 + 106,000 = 357,000, yearly).

How Safe is Chiropractic?

The most notorious adverse event with a supposed link to chiropractic spinal manipulation is Cervical Artery Dissection. Allegations of cervical artery dissection caused by chiropractic spinal manipulation have appeared in the published literature for decades. However, recent large critical reviews of the topic have appeared in the scientific literature, and they question the causation between cervical spine manipulation and cervical artery dissection. Some of this literature is reviewed below.


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

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

This study included all residents of Ontario, CAN, over a period of 9 years, amounting to 109,020,875 person years of observation. Restating, this article had more than 100 million person years of observation. Associations between chiropractic visit and vertebral artery dissection versus primary care physician (PCP) visits and vertebral artery dissection were compared.

The authors found that there were associations between both chiropractic visit and vertebral artery dissection, and PCP visit and vertebral artery dissection. The authors noted:

“The association for chiropractor visit was not greater than for PCP visit. This data was interpreted as evidence that a confounder such as neck pain may account for the association between chiropractor visit and vertebral artery dissection.”

“Cassidy et al. hypothesized that, although an association between chiropractor visits and vertebrobasilar artery stroke is present, it may be fully explained by neck pain and headache.”

“The authors conclude that, since patients with vertebrobasilar stroke were as likely to visit a PCP as they were to visit a chiropractor, these visits were likely due to pain from an existing dissection.”

“We found no evidence of excess risk of vertebral artery stroke associated 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.”

“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.”

“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 January of 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 (7):

“A population-based case-series of Ontario patients who develop a vertebrobasilar artery stroke after seeing a chiropractor”

These authors noted:

“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 January 2011, The Open Neurology Journal published an “open access” editorial by Drs. Dean Smith and Gregory Cramer, titled (8):

“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, and,

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

“First, evidence is mounting that the association between spinal manipulation and stroke is coincidental rather than causal and reflects the natural history of the disorder.” (ref 7)

“The largest population-based study to date was conducted by Cassidy et al. and included all vertebrobasilar artery (VBA) strokes in Ontario, Canada over a period of 9 years. The authors found no evidence of excess risk (i.e. no risk) of VBA stroke associated with chiropractic care.” (ref 6)

“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.” (ref 6, 7)

“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.”

“Spinal manipulations delivered by licensed chiropractors do not fulfill the criteria for major trauma and should not be considered major trauma.”


The biomechanics of cervical spine manipulation and vertebral artery stress is important. The world leader on this type of biomechanical assessment is Walter Herzog, PhD, from the University of Calgary, CAN. In 2012, Dr. Herzog and colleagues published a study in the Journal of Electromyography and Kinesiology titled (9):

Vertebral artery strains during high-speed, low amplitude cervical spinal manipulation

Dr. Herzog notes that spinal manipulative therapy (SMT) is recognized as an effective treatment modality for many back, neck and musculoskeletal problems. Yet, one of the major issues of the use of SMT is its safety, especially with regards to neck manipulation and the risk of stroke. It has been assumed [wrongly as per this study] that the vertebral artery (VA) experiences considerable stretch during extension and rotation of the neck, which may lead to occlusions and damage to the VA, predisposing the patient to stroke. Therefore, this study presents the first ever data on the mechanics between C2/C1 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. Dr. Herzog and colleagues 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.”

“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.”


In 2015, a study was published in the journal Chiropractic & Manual Therapies, and titled (10):

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 (6), and to investigate the association between chiropractic care and vertebral artery stroke; and compare it to the association between recent primary care physician (PCP) 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.”

“Our results increase confidence in the findings of a previous study [6], which concluded there was no excess risk of vertebral artery stroke associated with chiropractic care compared to primary care.”


In 2016, a study from the Department of Neurosurgery, Penn State Hershey Medical Center, and the Department of Neurosurgery, Johns Hopkins University School of Medicine, was published in the journal Cureus, and titled (11):

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

The authors note that case reports and case control studies have suggested an association between chiropractic neck manipulation and cervical artery dissection (CAD), but a causal relationship has not been established. 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). Their meta-analysis used 2 class II and 4 class III studies.These authors 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.”

“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 quality of the published literature on the relationship between chiropractic manipulation and CAD is very low. Our analysis shows a small association between chiropractic neck manipulation and cervical artery dissection. This relationship may be explained by the high risk of bias and confounding in the available studies, and in particular by the known association of neck pain with CAD and with chiropractic manipulation.”

“Cervical artery dissection is a rare event, creating a significant challenge for those who wish to understand it. A prospective, randomized study design is best suited to control for confounders, but given the infrequency of dissection, performing such a study would be logistically and also ethically challenging.”

“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.”


Few people, health care providers, politicians, and government officials are aware that every year hundreds of thousands of Americans are killed or suffer serious adverse events as a consequence of medical error and “fallout.” In contrast, chiropractic spinal manipulation, even to the cervical spine, is incredibly safe.

Chiropractic students and chiropractors are extensively trained in spinal anatomy and spinal biomechanics. They are also extensively trained in the science and art of spinal adjusting (specific directional manipulation).

The studies presented here suggest that the symptoms associated with spontaneous vertebral artery dissection may bring the patient into chiropractic offices, and as such, the chiropractic manipulation is actually not causing the dissection.


“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.”


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