Flaws in a Recent Vertebral Artery Dissection Study by Smith et al

Abstract

The recent publication by Smith et al1Smith WS Johnston SC Skalabrin EJ Weaver M Azari P Albers GW et al.Spinal manipulative therapy is an independent risk factor for vertebral artery dissection.Neurology. 2003; 60: 1424-1428Crossref PubMed Scopus (220) Google Scholar in Neurology addressing vertebral artery dissection (VAD) represents another chapter of regrettable studies that, despite serious flaws that raise substantial questions as to their internal validity, go to great lengths to selectively disparage the advisability of performing cervical manipulations as a means of patient care while obscuring the larger picture.2Lee KP Carlini WG McCormick GF Walters GW Neurologic complications following chiropractic manipulation: a survey of California neurologists.Neurology. 1995; 45: 1213-1215Crossref PubMed Scopus (186) Google Scholar, 3Bin Saeed A Shuaib A Al-Sulaiti G Emery D Vertebral artery dissection: warning symptoms, clinical features and prognosis in 26 patients.Can J Neurol Sci. 2000; 27: 292-296Crossref PubMed Scopus (155) Google Scholar, 4Hufnagel A Hammers A Schonle P-W Bohm K-D Leonhardt G Stroke following chiropractic manipulation of the cervical spine.J Neurol. 1999; 246: 683-688Crossref PubMed Scopus (143) Google Scholar, 5Norris JW Beletsky V Nadareishvilli ZG Canadian Stroke Consortium.Can Med Assoc J. 2000; 163: 38-40PubMed Google Scholar, 6Rothwell DM Bondy SJ Williams JI Chiropractic manipulation and stroke: a population-based case-control study.Stroke. 2001; 32: 1054-1060Crossref PubMed Google Scholar Larger picture in this instance means (1) the well-documented benefits of this procedure; (2) the equally well-chronicled risks of alternatives to cervical manipulation (including the use of medications, which is deeply entrenched in our society and obviously far more prevalent than any applications of manipulation); and (3) any evidence showing that the mechanisms of cervical manipulation provide trauma to the vertebrobasilar system, leading to dissections in the normal vertebral artery (VA). The fact that the Smith et al1Smith WS Johnston SC Skalabrin EJ Weaver M Azari P Albers GW et al.Spinal manipulative therapy is an independent risk factor for vertebral artery dissection.Neurology. 2003; 60: 1424-1428Crossref PubMed Scopus (220) Google Scholar study has been so extensively and immediately propagated in the printed and televised media, in contrast to the many investigations that have supported cervical manipulations with no reports of substantial side effects,7McCrory DC Penzien DB Hasselblad V Gray RN Evidence report: behavioral and physical treatments for tension-type and cervicogenic headache. Foundation for Chiropractic Education and Research, Des Moines2001: 58-61Google Scholar, 8Boline P Kassak K Bronfort G Nelson C Anderson AV Spinal manipulation vs. amiltriptyline for the treatment of chronic tension-type headaches: a randomized clinical trial.J Manipulative Physiol Ther. 1995; 18: 148-154PubMed Google Scholar, 9Hoyt WH Shaffer F Bard DA Benesler JS Blankenhorn GD Gray JH et al.Osteopathic manipulation in the treatment of muscle contraction headache.J Am Osteopath Assoc. 1979; 78: 322-325PubMed Google Scholar, 10Nilsson N A randomized controlled trial of the effect of spinal manipulation in the treatment of cervicogenic headache.J Manipulative Physiol Ther. 1995; 18: 435-440PubMed Google Scholar, 11Nilsson N Christensen HW Hartvigsen J The effect of spinal manipulation in the treatment of cervicogenic headaches.J Manipulative Physiol Ther. 1997; 20: 326-330PubMed Google Scholar, 12Parker G Tupling H Pryor D A controlled trial of cervical manipulation for migraine.Aust N Z J Med. 1978; 8: 589-593Crossref PubMed Scopus (79) Google Scholar, 13Jensen IK Nielsen FF Vosmar L An open study comparing manual therapy with the use of cold packs in the treatment of post-traumatic headache.Cephalalgia. 1990; 10: 243-250Google Scholar, 14Nelson C Bronfort G Evans R Boline P Goldsmith C Anderson AV The efficacy of spinal manipulation, amitriptyline, and the combination of both therapies for the prophylaxis of migraine headache.J Manipulative Physiol Ther. 1998; 21: 511-519PubMed Google Scholar, 15Whittingham W Ellis WB Molyneux TP The effect of manipulation [toggle recoil] for headaches with upper cervical joint dysfunction: a pilot study.J Manipulative Physiol Ther. 1994; 17: 369-375PubMed Google Scholar, 16Mootz RD Dhami MSI Hess JA Cook RD Schorr DB Chiropractic treatment of chronic episodic tension type headache in male subjects: a case series analysis.J Can Chiropr Assoc. 1994; 38: 152-159Google Scholar, 17Droz JM Crot F Occipital headaches: statistical results in the treatment of vertebrogenic headache.Ann Swiss Chiropr Assoc. 1985; 8: 127-136Google Scholar, 18Vernon HT Spinal manipulation and headaches of cervical origin.J Manipulative Physiol Ther. 1982; 5: 109-112PubMed Google Scholar, 19Wight JS Migraine: a statistical analysis of chiropractic treatment.Chiropr J. 1978; 12: 363-367Google Scholar, 20Stodolny J Chmielewski H Manual therapy in the treatment of patients with cervical migraine.Man Med. 1989; 4: 49-51Google Scholar, 21Turk Z Ratkolb O Mobilization of the cervical spine in chronic headaches.Man Med. 1987; 3: 15-17Google Scholar, 22Bove G Nilsson N Spinal manipulation in the treatment of episodic tension-type headache.JAMA. 1998; 280: 1576-1579Crossref PubMed Scopus (123) Google Scholar, 23Davis PT Hulbert JR Kassak KM Meyer JJ Comparative efficacy of conservative medical and chiropractic treatments for carpal tunnel syndrome: a randomized clinical trial.J Manipulative Physiol Ther. 1998; 21: 317-326PubMed Google Scholar, 24Froehle RM Ear infection: a retrospective study examining improvement from chiropractic care and analyzing for influencing factors.J Manipulative Physiol Ther. 1996; 19: 169-177PubMed Google Scholar, 25Fallon J The role of chiropractic adjustment in the care and treatment of 332 children with otitis media.J Clin Chiropr Pediatr. 1997; 2: 167-183Google Scholar, 26Degenhardt BF Kuchera ML Efficacy of osteopathic evaluation and manipulative treatment in reducing the morbidity of otitis media in children.J Am Osteopath Assoc. 1994; 94: 673Google Scholar, 27Klougart N Nilsson N Jacobsen J Infantile colic treated by chiropractors: a prospective study of 316 cases.J Manipulative Physiol Ther. 1989; 12: 281-288PubMed Google Scholar, 28Wiberg JMM Nordsteen J Nilsson N The short-term effect of spinal manipulation in the treatment of infantile colic: a randomized controlled trial with a blinded observer.J Manipulative Physiol Ther. 1999; 22: 517-522Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar, 29Reed WR Beavers S Reddy SK Kern G Chiropractic management of primary nocturnal enuresis.J Manipulative Physiol Ther. 1994; 17: 596-600PubMed Google Scholar, 30Yates RG Lamping DL Abram NL Wright C Effects of chiropractic treatment on blood pressure and anxiety: a randomized, controlled trial.J Manipulative Physiol Ther. 1989; 11: 484-488Google Scholar represents a major disservice to the American public, which threatens its access to the best alternatives in health care available. This critique will be discussed from 2 vantage points, in terms of both internal flaws and its analysis in the larger context. To begin, there is no indication that the 151 dissection cases were randomly identified; only the control patients were so chosen. The fact that some demographic features of the 2 groups such as age or dimensions of the arteries involved differ implies a more basic and global characteristic pertaining to arterial dissections that lies outside cervical adjustments, a point to be discussed in detail below regarding spontaneous arterial dissections. This would seem to be particularly true because the number of patients in which spinal manipulative therapy (SMT) has been reported to occur within 30 days is just 7, compared with 3 in the control group. The differential of just 4 individuals between the 2 groups is a paltry number, indeed, on which to base association, let alone any hint of causality over the extended period of 30 days. The fact that 2 patients actually experienced a stroke or transient ischemic attack immediately after SMT is clearly more compelling, but even here the authors fail to make a distinction between stroke and transient ischemic attack, which is far more benign. The fact that strokes could happen at the time of SMT, but not necessarily reflect it as a risk factor, will be discussed below. To one's amazement, the authors excluded a larger number of patients (8) because of “iatrogenic dissection with or without stroke” than actually were listed as having a dissection within 30 days of SMT.7McCrory DC Penzien DB Hasselblad V Gray RN Evidence report: behavioral and physical treatments for tension-type and cervicogenic headache. Foundation for Chiropractic Education and Research, Des Moines2001: 58-61Google Scholar In addition to making the low number of dissection cases within 30 days of SMT appear even more absurd, the authors raise the more serious question as to exactly what had caused the “iatrogenic dissections in the first place.” By most common definitions, iatrogenic is thought to have been brought on by medical interventions, a point to be discussed in more detail below. This study bases its conclusions only on the association of a single observation (presence of VAD) with previous events recalled by the patient. There are no baseline (control) readings to accompany this. One could argue that, without a control hospital laboratory finding (eg, elevated blood urine creatinine or presence of an arterial artery occlusion), the frequencies of possible precipitating events before the primary finding and the presence of arterial artery dissection are meaningless. By the reasoning put forth in this study, we would be forced to the rather strange conclusion that patients who recall cervical manipulation before their yielding elevated urine creatinine, for example, could be used as evidence that this form of intervention is necessarily associated with the aberrant blood chemistry levels obtained. Other than SMT, the authors have produced no indication that cervical manipulations were administered to every patient listed, so their attempts to link VADs and manipulation become that much more problematic. Until an actual relationship is struck between the location and actual number of adjustments and vertebral dissections is given and until some light can be shed on the mechanisms that could produce this result, any speculation of causality of manipulation and arterial dissection gleaned from the data in this study must be greeted with only the most extreme skepticism. Furthermore, the authors appear to have given little consideration to the fact that cerebrovascular accidents (CVAs) appear to be a cumulative rather than a traumatic event. This fact is emphatically driven home in that no less than 68 everyday activities have been implicated in disrupting cerebral circulation.31Rome PL Perspective: an overview of comparative considerations of cerebrovascular accidents.Chiropr J Aust. 1999; 29: 87-102Google Scholar, 32Terrett AGL Vascular accidents from cervical spine manipulation.J Aust Chiropr Assoc. 1987; 17: 15-24Google Scholar, 33Terrett AGL Vertebral stroke following manipulation. National Chiropractic Mutual Insurance Company, West Des Moines (IA)1996: 15Google Scholar Among those activities listed, 18 have actually been associated with vascular accidents but are decidedly nonmanipulative (Table 1).33Terrett AGL Vertebral stroke following manipulation. National Chiropractic Mutual Insurance Company, West Des Moines (IA)1996: 15Google ScholarTable 1Nonmanipulative manuevers associated with CVAs38Terrett AGJ Malpractice avoidance for chiropractors 1. Vertebrobasilar stroke following manipulation. National Chiropractic Mutual Insurance Company, Des Moines1996: 60-80Google ScholarChildbirthBy surgeon or anesthetist during surgeryCalisthenicsYogaOverhead workNeck extension during radiographyNeck extension for a bleeding noseTurning the head while driving a vehicleArcheryWrestlingEmergency resuscitationStar gazingSleeping positionSwimmingRap dancingFitness exerciseBeauty parlor strokeTai Chi Open table in a new tab The risk of fatal stroke after cervical manipulation has been assessed in an exhaustive systematic literature review of many sources to be 3 per 10 million manipulations34Hurwitz EL Aker PD Adams AH Meeker WC Shekelle PG Manipulation and mobilization of the cervical spine: a systematic review of the literature.Spine. 1996; 21: 1746-1760Crossref PubMed Scopus (405) Google Scholar or about .00025%.35Dabbs V Lauretti W A risk assessment of cervical manipulation vs. NSAIDS for the treatment of neck pain.J Manipulative Physiol Ther. 1995; 18: 530-536PubMed Google Scholar The mortality rate from stroke in the general population in 1992 and 1993 was .00057%, which raises the possibility that the death rate from stroke in the general population could conceivably be higher than that among chiropractic patients.36Myler L A risk assessment of cervical manipulation vs. NSAIDs for the treatment of neck pain.J Manipulative Physiol Ther. 1996; 19: 357PubMed Google Scholar Given the frequency of significant consequences from cervical manipulations (6 per 10 million manipulations or .0006%)34Hurwitz EL Aker PD Adams AH Meeker WC Shekelle PG Manipulation and mobilization of the cervical spine: a systematic review of the literature.Spine. 1996; 21: 1746-1760Crossref PubMed Scopus (405) Google Scholar and given the many lifestyle activities shown above to trigger CVAs, it would seem nearly impossible, as this study has done, to attribute the VADs reported at indefinite time periods after chiropractic manipulation to the latter. This association, based on a vague recollection of the patient of events in the past, cannot be counted on to have definitively identified spinal manipulation as a causative event. Identifying the chiropractor in this association is even more problematic, as will be shown immediately below. Did the 7 cases of VAD, attributed to cervical manipulation in the study, actually follow manipulation by a licensed chiropractor? There is no validation of this fact in the study as reported. The actual number of iatrogenic complications specifically ascribed to chiropractic has been shown to be significantly overestimated because the practitioner actually involved is, in many cases, a nonchiropractor. Rather, a major portion of these accidents have occurred at the hands of an individual with inadequate professional training but incorrectly represented in the medical literature as a chiropractor. This particular review is alarming in that it suggests that for many years chiropractors have been overrepresented (possibly in a systematic manner) in the literature as having brought on VAs.37Terrett AGJ Misuse of the literature by medical authors in discussing spinal manipulative therapy injury.J Manipulative Physiol Ther. 1995; 18: 203-210PubMed Google Scholar, 38Terrett AGJ Malpractice avoidance for chiropractors 1. Vertebrobasilar stroke following manipulation. National Chiropractic Mutual Insurance Company, Des Moines1996: 60-80Google Scholar Risks are inherent in every medical procedure or lifestyle activity that we encounter. In terms of interventions of the spine, chiropractic has been shown to be many orders of magnitude safer than medication or surgery. Assuming that each patient receives an average of 10 manipulations in treatment,61Carey TS Garrett J Jackman A McLaughlin C Fryer J Smucker DR The outcomes and costs of care for acute low back pain among patients seen by primary care practitioners, chiropractors, and orthopedic surgeons.N Engl J Med. 1995; 333: 913-917Crossref PubMed Scopus (473) Google Scholar death rates after cervical manipulation calculate to anywhere between 1/100 to 1/400 the rates seen in the use of nonsteroidal anti-inflammatory drugs for the same condition.35Dabbs V Lauretti W A risk assessment of cervical manipulation vs. NSAIDS for the treatment of neck pain.J Manipulative Physiol Ther. 1995; 18: 530-536PubMed Google Scholar, 39Gabriel SE Jaakkimainen L Bombardier C Risk of serious gastrointestinal complications related to the use of nonsteroidal anti-inflammatory drugs: a meta-analysis.Ann Intern Med. 1991; 115: 787-796Crossref PubMed Scopus (1228) Google Scholar Death rates from lumbar spine surgeries have been reported to be 300 times higher than the rate produced by CVAs in spinal manipulation40Deyo RA Cherkin DC Loesser JD Bigos SJ Ciol MA Morbidity and mortality in association with operations on the lumbar spine.J Bone Joint Surg. 1992; 74A: 536-543Google Scholar, 41Boullet R Treatment of sciatica: a comparative survey of the complications of surgical treatment and nucleolysis with chymopapain.Clin Orthop. 1990; 251: 144-152PubMed Google Scholar; for cervical surgeries, recent death rates have been estimated to be 700-fold greater.40Deyo RA Cherkin DC Loesser JD Bigos SJ Ciol MA Morbidity and mortality in association with operations on the lumbar spine.J Bone Joint Surg. 1992; 74A: 536-543Google Scholar As Rome31Rome PL Perspective: an overview of comparative considerations of cerebrovascular accidents.Chiropr J Aust. 1999; 29: 87-102Google Scholar has pointed out, risks of virtually all medical procedures ranging from the taking of blood samples42Horowitz SH Peripheral nerve injury and causalgia secondary to routine venipuncture.Neurology. 1994; 44: 962-964Crossref PubMed Google Scholar; use of vitamins,43Caswell A MIMS Annual. Australian ed. 22nd ed. MediMedia Publishing, St. Leonards, New South Wales1998Google Scholar drugs,43Caswell A MIMS Annual. Australian ed. 22nd ed. MediMedia Publishing, St. Leonards, New South Wales1998Google Scholar and “natural” medications44Anonymous Readers' Q & A.Aust Med. October; 1998; 5: 18Google Scholar; and vaccinations45Burgess MA McIntyre PB Heath TC Rethinking contraindications to vaccination.Med J Aust. 1998; 168: 476-477PubMed Google Scholar are routinely accepted by the public as a matter of course. How risks are interpreted is another matter. The VA rate for chiropractic as described above, although extremely low, does represent a challenge to be improved on. On the other hand, as Rome31Rome PL Perspective: an overview of comparative considerations of cerebrovascular accidents.Chiropr J Aust. 1999; 29: 87-102Google Scholar points out, such phenomena as (1) patient informed consent, (2) “low and acceptable rates of complications” stated in a policy by the Australian College of Ophthalmologists,46Toy MA Vision for laser surgery loses its shine—seeing is believing.Age. 1998; (Nov 7): 15PubMed Google Scholar or (3) “trading off” risks of surgeries and stroke as stated in a recent study of endarterectomies47European Carotid Surgery Trialists' Collaborative GroupRandomized trial of endarterectomy for recently symptomatic carotid stenosis: final results of the MRC European Carotid Surgery Trial (ECST).Lancet. 1998; 351: 1379-1387Abstract Full Text Full Text PDF PubMed Scopus (2945) Google Scholar all attest to the fact that certain levels of risk have been habitually accepted in our society until improvements can be made. Why should chiropractic be singled out as having an unacceptable risk? In his distinction of specific provider types associated with CVAs, Terrett37Terrett AGJ Misuse of the literature by medical authors in discussing spinal manipulative therapy injury.J Manipulative Physiol Ther. 1995; 18: 203-210PubMed Google Scholar has identified 34 deaths associated with manipulation over 61 years worldwide. For the sake of comparison, 12,000 deaths per year from unnecessary surgery, 7000 deaths per year from medication errors in hospitals, approximately 80,000 deaths per year from nosocomial infections in hospitals, and 106,000 deaths per year from nonerror, adverse effects of medications have been recently reported with regard to conventional medicine.48Leape L Unnecessary surgery.Annu Rev Public Health. 1992; 13: 363-383Crossref PubMed Scopus (50) Google Scholar, 49Phillips D Christenfeld N Glynn L Increase in US medication-error deaths between 1983 and 1993.Lancet. 1998; 351: 643-644Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar, 50Lazarou J Pomeranz B Corey P Incidence of adverse drug reactions in hospitalized patients.JAMA. 1998; 279: 1200-1205Crossref PubMed Scopus (4099) Google Scholar These data are presented simply to prevent our losing perspective on the entire issue of risk/benefit ratios raised by the study published in Neurology.1Smith WS Johnston SC Skalabrin EJ Weaver M Azari P Albers GW et al.Spinal manipulative therapy is an independent risk factor for vertebral artery dissection.Neurology. 2003; 60: 1424-1428Crossref PubMed Scopus (220) Google Scholar This discussion would not be complete without considering acceptable lifestyle risks, which should be common knowledge if we are to evaluate the safety of any health care intervention, chiropractic or otherwise. Table 2 from the study of Dinman51Dinman BD The reality and acceptance of risk.JAMA. 1980; 244: 1226-1228Crossref PubMed Scopus (41) Google Scholar clearly indicates that the risk of death per person per year in many of the activities that we accept as normal and engage in are for the most part many orders of magnitude greater than those seen in serious VA complications after chiropractic manipulation. Once again, we must be skeptical if cervical chiropractic manipulation seems to have been singled out as a particularly conspicuous and noxious threat to our livelihood.Table 2Voluntary risks51Dinman BD The reality and acceptance of risk.JAMA. 1980; 244: 1226-1228Crossref PubMed Scopus (41) Google ScholarVoluntary riskRisk of death/position/yearSmoking: 20 cigarettes/day1 in 200Drinking: 1 bottle of wine/day1 in 13,300Soccer, football1 in 25,500Automobile racing1 in 1000Automobile driving (United Kingdom)1 in 5900Motorcycling1 in 50Rock climbing1 in 7150Taking contraceptive pills1 in 5000Power boating1 in 5900Canoeing1 in 100,000Horse racing1 in 740Amateur boxing1 in 2 millionProfessional boxing1 in 14,300Skiing1 in 4350Pregnancy (United Kingdom)1 in 4350Abortion: legal <12 weeks1 in 50,000Abortion: legal > 14 weeks1 in 5000 Open table in a new tab From a mechanistic viewpoint, the most direct means of assessing the effects of spinal manipulative therapy on the integrity of the VAs would be to directly measure how the forces anticipated during manipulations might be transmitted through the various skeletal and soft tissue layers of the cervical milieu to the region of the VA and how such forces compare with the limits of arterial integrity assessed by deliberately stretching the VA until it ruptures. Such a study was recently accomplished at the University of Calgary on the VAs excised from unembalmed postrigor patients who had died within the past 72 hours.52Symons BP Herzog W Internal forces sustained by the vertebral artery during spinal manipulative therapy.J Manipulative Physiol Ther. 2002; 25: 504-510Abstract Full Text PDF PubMed Scopus (75) Google Scholar In this investigation, the distal C0-1 and proximal C6-subclavian loops of the VAs were exposed and fitted with a pair of piezoelectric ultrasonic crystals. Strains between each crystal pair were recorded during range of motion testing, diagnostic tests, and a variety of procedures employed in spinal manipulation. Afterward, the VA was dissected and strained on a materials testing machine until mechanical failure occurred. For manipulation, the elongations of the C0-1 and C6-subclavian artery segments of the VA were 6.2% and 2.1%, respectively. For normal head rotation, on the other hand, these elongations were, respectively, 12.5% and 4.8%. The elongations of these same regions needed to reach VA failure were 53.1% and 62.3%, respectively. Two conclusions are readily apparent: (1) the values measured during spinal manipulative therapy were less than those recorded during range of motion and diagnostic testing; and (2) the VA strains measured during spinal manipulation were less than 1/9 those needed to achieve arterial failure.52Symons BP Herzog W Internal forces sustained by the vertebral artery during spinal manipulative therapy.J Manipulative Physiol Ther. 2002; 25: 504-510Abstract Full Text PDF PubMed Scopus (75) Google Scholar The implications of this study shed considerable light on the controversy regarding VADs and spinal manipulation. First, it is evident that the forces experienced during spinal manipulation are virtually an order of magnitude below those needed to produce an arterial failure in a single event. Secondly, it is apparent that routine neck maneuvers during the assessments (rather than the manipulations) registered greater forces in the region of the VAs. This immediately raises the possibility that spontaneous rather than induced CVAs are likely to occur in the VA, an issue that will be explored in depth in the following section. There are a number of significant cautionary notes that must be sounded to this study, however:1.The portion of the artery most commonly involved in VADs associated with spinal manipulation (C1-2, as pointed out earlier) was not measured; rather, the entire VA was used to obtain mechanical failure points53Good C Letter to the editor.J Manipulative Physiol Ther. 2003; 26: 338-339Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar;2.Stretch by tensile forces rather than compression by combined forces (particularly at the C2 foramen, proposed to be the actual force causing damage during manipulation)53Good C Letter to the editor.J Manipulative Physiol Ther. 2003; 26: 338-339Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar was measured, which may not reflect the suspected type of artery deformation occurring in patients;3.The strain created to the thrust side VA when the neck is fully rotated contralaterally, representing the most forceful manipulation, was not measured53Good C Letter to the editor.J Manipulative Physiol Ther. 2003; 26: 338-339Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar;4.The ranges of motion from the 80- to 99-year-old cadavers would be expected to be more restricted than those more typical of younger patients seen in chiropractic offices, limiting the strains on the VAs that were measured by the researchers and perhaps not representative of those seen in actual practice52Symons BP Herzog W Internal forces sustained by the vertebral artery during spinal manipulative therapy.J Manipulative Physiol Ther. 2002; 25: 504-510Abstract Full Text PDF PubMed Scopus (75) Google Scholar;5.There were wide variations in force ranges (4N-18N) and strains (31%-75%)52Symons BP Herzog W Internal forces sustained by the vertebral artery during spinal manipulative therapy.J Manipulative Physiol Ther. 2002; 25: 504-510Abstract Full Text PDF PubMed Scopus (75) Google Scholar;6.Preparing the arterial specimens in ultrasound gel may have artificially increased their flexibility;7.One may question whether the overall arterial failures observed bear compelling resemblance to the intimal tearing experienced in vivo during arterial dissections; and finally8.Because arterial dissections may well represent the culmination of multiple arterial insults as outlined in the ensuing text, it is necessary that this experiment be repeated to assess arterial integrity after dozens and perhaps hundreds of applied stretches to the VA. The most compelling information that needs to be brought forward to bring the debate about cervical manipulations onto a level playing field pertains to the fact that a significant number and most likely the majority of vertebral artery dissections happen to be spontaneous cervical artery dissections (sCADs). The numerous reports addressing both the frequency of occurrence of VADs and their association with virtually any activity associated with turning the head should reduce the usefulness of attributing strokes to cervical manipulations to an academic exercise. As shown in Table 3, the annual incidence of spontaneous VADs in hospital settings has been estimated to occur at the rate of 1 to 1.5 per 100,000 patients.54Schievink WT Mokri B O'Fallon WM Recurrent spontaneous cervical-artery dissection.N Engl J Med. 1994; 330: 393-397Crossref PubMed Scopus (436) Google Scholar The corresponding VAD incidence rate in community settings has been reported to be twice as high.55Schievink WT Mokri B Whisnant JP Internal carotid artery dissection in a community: Rochester, Minnesota, 1987-1992.Stroke. 1993; 24: 1678-1680Crossref PubMed Scopus (289) Google Scholar, 56Giroud M Fayolle H Andre N Dumas R Becker F Martin D et al.Incidence of internal carotid artery dissection in the community of Dijon [Letter].J Neurol Neurosurg Psychiatry. 1994; 57: 1443Crossref PubMed Scopus (183) Google Scholar Using an estimated value of 10 from the literature to represent an average number of manipulations per patient per episode,61Carey TS Garrett J Jackman A McLaughlin C Fryer J Smucker DR The outcomes and costs of care for acute low back pain among patients seen by primary care practitioners, chiropractors, and orthopedic surgeons.N Engl J Med. 1995; 333: 913-917Crossref PubMed Scopus (473) Google Scholar it becomes apparent that the proposed exposure rate for CVAs attributed to spinal manipulation is equivalent to the spontaneous rates for cervical arterial dissections as reported.54Schievink WT Mokri B O'Fallon WM Recurrent spontaneous cervical-artery dissection.N Engl J Med. 1994; 330: 393-397Crossref PubMed Scopus (436