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Chiropractic Safety Research
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Passive Care:
Adjustments - Safety (Stroke)
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1. Symons, B et al. Internal forces sustained by the vertebral artery during spinal manipulative therapy. J Manipulative Physiol Ther. 2002 Oct; 25(8):504-10.
Spinal manipulative therapy (SMT) has been established as a clinically effective modality for the management of several musculoskeletal disorders. One major issue with the use of SMT is its safety, especially with respect to neck manipulation and the risk of stroke in the vertebrobasilar system. The objective of this study was to quantify the strains and forces sustained by the vertebral artery (VA) in situ during SMT.
This was a cadaveric study involving six unembalmed postrigor cadavers.
{Panjabi et a. reported that the biomechanical properties of cadaveric spinal specimens did not alter significantly even after 232 days of storage at -20°C, and Yamada showed that the tensile properties of common carotid arteries harvested from cattle did not change appreciably after 4 days of refrigeration in normal saline solution.}
The cephalad/distal (C0-C1) and caudad/proximal (C6-subclavian artery) loops of the vertebral artery were carefully exposed and instrumented with a pair of piezoelectric ultrasonographic crystals. The strains between each crystal pair were recorded during range of motion testing and diagnostic tests and during a variety of SMT procedures. The vertebral artery was then dissected free and strained on a materials testing machine until mechanical failure occurred.
RESULTS:
SMT performed on the contralateral side of the cervical spine resulted in an average strain of 6.2% distal (C0-C1) loop of the vertebral artery and a 2.1% strain to the proximal (C6) loop. These values were similar to or lower than the strains recorded during diagnostic and range of motion testing.
Failure testing demonstrated that the vertebral arteries could be stretched to 139% to 162% of their resting length before mechanical failure occurred. Therefore the strains sustained by the vertebral artery during SMT represent approximately one ninth of the strain at mechanical failure.
CONCLUSIONS:
SMT resulted in strains to the vertebral arteries that were almost 10 times lower than the strains required to mechanically disrupt it.
We conclude that under normal circumstances, a single typical (high-velocity/low-amplitude) SMT thrust is very unlikely to mechanically disrupt the vertebral artery.
2. Chestnut, J. The Stroke Issue: Paucity of Valid Data, Plethora of Unsubstantiated Conjecture. J Manipulative Physiol Ther 2004;27:368-72.
This paper reviews the literature on cervical spine manipulation and the risk of stroke.
This review is based on the opinion of one author, Dr. James L. Chestnut.
It is a compelling review of the evidence (or as this author so thoroughly publishes; lack of evidence) regarding the debate between the allopathic community and Chiropractic cervical manipulation and subsequent risk of stroke.
The first paragraph sets the tone for the remainder of this short 4+ page commentary and reads:
"The debate regarding chiropractic cervical adjustments (manipulation) and the potential risk of vertebrobasilar artery (VBA) dissection has become increasingly more emotional and political than scientific.
As a scientist and a practitioner, I find it disconcerting that the published literature contains more unsubstantiated misinformation than useful scientifically valid information. Depending on which "expert" a person references, the chance of VBA dissection after chiropractic adjustment ranges anywhere from 1 in 5000 to 1 in 5 million.
How is such a range of expert opinion possible?
The answer, quite bluntly, is due to the fact that none of these risk estimates are based on valid scientific information."
The commentary then continues to point out the flaws in the extrapolation of data for the most commonly cited literature on this topic, especially with regards to:
(1) Norris JW, Beletsky V, Nadareishvili ZG. Sudden neck movement and cervical artery dissection. The Canadian Stroke Consortium. CMAJ 2000;163:38-40.
(2) Rothwell D, Bondy S, Williams J. Chiropractic manipulation and stroke: a population-based case-control study. Stroke 2001;32:1054-60.
The commentary is concluded with what the author titles "Concluding Summary of Facts." In the section the author lists 8 facts about cervical manipulation and risk of stroke. Listed below is as summary of the 8 facts according to this author:
Fact 1:
The vast majority of VBA dissections and occlusions (and all forms of stroke) occur without any association to chiropractic cervical adjustment.
Fact 2:
There are millions of chiropractic cervical adjustments performed every year without incidence of VBA dissection, occlusion, or stroke.
Fact 3:
There are no valid scientific data available to establish the cause of any VBA dissection, because the only available data are from studies with methodologies incapable of validly establishing causation.
Fact 4:
There are no valid data that can identify any variable as the cause of any VBA dissection.
Fact 5:
The most commonly reported VBA dissection case reports in the literature have no identified precipitating factors and are classified as spontaneous.
This can skew the published data and makes any reference to rate of risk of any particular precipitating event invalid speculation. There are no valid data available from which to extract rates of risk of VBA dissection or occlusion associated with any precipitating event.
Fact 6:
The only data available on the forces transmitted to the vertebral artery during chiropractic adjustment indicate that a chiropractic adjustment represents less force to the vertebral artery than mundane common activities of daily living (ie, less force than turning the head within the normal range of motion).
*This research study is summarized on this website as Symons, B et al. Internal forces sustained by the vertebral artery during spinal manipulative therapy. J Manipulative Physiol Ther. 2002 Oct; 25(8):504-10.
Fact 7:
Every VBA dissection victim in history has had recent exposure to mundane common activities of daily living that have been identified as a common precipitating event in VBA dissection and occlusion and thus cannot be eliminated as the possible cause.
Fact 8:
The fact that VBA dissection is so rare and the fact that so many millions of chiropractic cervical adjustments are performed each year would mean that a valid study to determine if there is a true risk from chiropractic cervical adjustment would require millions of subjects.
Considering that common medical treatments (NSAIDS, surgery) for neck pain and other health problems stemming from the joints, nerves, and muscles of the neck carry a much greater known risk than that hypothesized with chiropractic adjustments and the fact that these are considered acceptable risks within the medical field, the importance of such a study does not seem to warrant the cost.
Considering that more than 98% of VBA dissections and occlusions are associated with events other than chiropractic cervical adjustment, it becomes obvious that studies to identify these factors warrant much more attention and resources.
3. Haldeman, S. et al. Clinical perceptions of the risk of vertebral artery dissection after cervical manipulation: the effect of referral bias. Spine J. 2002 Sep-Oct; 2(5):334-42.
Recent surveys have reported that many neurologists will encounter cases of vertebral artery dissection that occur at various times after cervical manipulation, whereas most practitioners of spinal manipulation are of the opinion that these events are extremely rare.
The objective of this study was to assess the effect of referral bias on the differences in perceived incidence of vertebral artery dissection after cervical manipulation between neurologists and chiropractors in Canada.
This study was a retrospective review of cases where neurological symptoms consistent with cerebrovascular ischemia were reported by chiropractors in Canada.
An analysis of data from a chiropractic malpractice insurance carrier (Canadian Chiropractic Protective Association [CCPA]) and results of a survey of chiropractors was performed to determine the likelihood that a vertebral artery dissection after cervical manipulation would be reported to practicing chiropractors. This was compared with the likelihood that a neurologist would be made aware of such a complication.
RESULTS:
For the 10-year period 1988 to 1997, there were 23 cases of vertebral artery dissection after cervical manipulation reported to the CCPA that represents 85% of practicing chiropractors in Canada.
Based on the survey, an estimated 134,466,765 cervical manipulations were performed during this 10-year period.
This gave a calculated rate of vertebral artery dissection after manipulation of 1:5,846,381 cervical manipulations.
Based on the number of practicing chiropractors and neurologists during the period of this study, 1 of every 48 chiropractors and one of every two neurologists would have been made aware of a vascular complication from cervical manipulation that was reported to the CCPA during their practice lifetime.
CONCLUSIONS:
The perceived risk after cervical manipulation by chiropractors and neurologists is related to the probability that a practitioner will be made aware of such an incident.
In active practice each patient who has a stroke after manipulation will likely be seen by only one chiropractor but by three or more neurologists partly explains the difference in experience and the perception of risk of these two professions.
This selection or referral bias is important in shaping the clinical opinions of the various disciplines and distorts discussion on the true incidence of these complications of cervical manipulation.
The nature of this study, however, describes the likelihood that a clinician will be made aware of such an event and cannot be interpreted as describing the actual risk of stroke after manipulation.
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