SPINE Volume 33, Number 4S, pp S176–S183 ©2008, Lippincott Williams & Wilkins
Risk of Vertebrobasilar Stroke and Chiropractic Care Results of a Population-Based Case-Control and Case-Crossover Study J. David Cassidy, DC, PhD, DrMedSc,*†‡ Eleanor Boyle, PhD,* Pierre Coˆte´, DC, PhD,*†‡ § Yaohua He, MD, PhD,* Sheilah Hogg-Johnson, PhD,† § Frank L. Silver, MD, FRCPC,¶ ! and Susan J. Bondy, PhD†
Study Design. Population-based, case-control and case-crossover study. Objective. To investigate associations between chiro- practic visits and vertebrobasilar artery (VBA) stroke and to contrast this with primary care physician (PCP) visits and VBA stroke. Summary of Background Data. Chiropractic care is popular for neck pain and headache, but may increase the risk for VBA dissection and stroke. Neck pain and head- ache are common symptoms of VBA dissection, which commonly precedes VBA stroke. Methods. Cases included eligible incident VBA strokes admitted to Ontario hospitals from April 1, 1993 to March 31, 2002. Four controls were age and gender matched to each case. Case and control exposures to chiropractors and PCPs were determined from health billing records in the year before the stroke date. In the case-crossover analysis, cases acted as their own controls. Results. There were 818 VBA strokes hospitalized in a population of more than 100 million person-years. In those aged ! 45 years, cases were about three times more likely to see a chiropractor or a PCP before their stroke than controls. Results were similar in the case control and case crossover analyses. There was no increased association between chiropractic visits and VBA stroke in those older than 45 years. Positive associations were found between PCP visits and VBA stroke in all age groups. Practitioner visits billed for headache and neck From the *Centre of Research Expertise for Improved Disability Outcomes (CREIDO), University Health Network Rehabilitation Solutions, Toronto Western Hospital, and the Division of Heath Care and Outcomes Research, Toronto Western Research Institute, Toronto, ON, Canada; †Department of Public Health Sciences, Management and Evaluation, University of Toronto, Toronto, ON, Canada; ‡Department of Health Policy, Management and Evalua- tion, University of Toronto, Toronto, ON, Canada; §Institute for Work & Health, Toronto, ON, Canada; ¶University Health Net- work Stroke Program, Toronto Western Hospital, Toronto, ON, Canada; and ! Division of Neurology, Department of Medicine, Fac- ulty of Medicine, University of Toronto, Toronto, ON, Canada. Supported by Ontario Ministry of Health and Long-term Care. P.C. is supported by the Canadian Institute of Health Research through a New Investigator Award. S.H.-J. is supported by the Institute for Work & Health and the Workplace Safety and Insurance Board of Ontario. The opinions, results, and conclusions are those of the authors and no endorsement by the Ministry is intended or should be inferred. The manuscript submitted does not contain information about medical device(s)/drug(s). University Health Network Research Ethics Board Approval number 05-0533-AE. Address correspondence and reprint requests to J. David Cassidy, DC, PhD, DrMedSc, Toronto Western Hospital, Fell 4-114, 399 Bathurst Street, Toronto, ON, CanadaM5T 2S8; E-mail: dcassidy@uhnresearch.ca
complaints were highly associated with subsequent VBA stroke. Conclusion. VBA stroke is a very rare event in the population. The increased risks of VBA stroke associated with chiropractic and PCP visits is likely due to patients with headache and neck pain from VBA dissection seek- ing care before their stroke. We found no evidence of excess risk of VBA stroke associated chiropractic care compared to primary care. Key words: vertebrobasilar stroke, case control stud- ies, case crossover studies, chiropractic, primary care, complications, neck pain. Spine 2008;33:S176–S183 Neck pain is a common problem associated with consid- erable comorbidity, disability, and cost to society. 1–5 In North America, the clinical management of back pain is provided mainly by medical physicians, physi- cal therapists and chiropractors. 6 Approximately 12% of American and Canadian adults seek chiropractic care annually and 80% of these visits result in spinal manipulation. 7,8 When compared to those seeking medical care for back pain, Canadian chiropractic pa- tients tend to be younger and have higher socioeco- nomic status and fewer health problems. 6,8 In On- tario, the average number of chiropractic visits per episode of care was 10 (median 6) in 1985 through 1991. 7 Several systematic reviews and our best- evidence synthesis suggest that manual therapy can benefit neck pain, but the trials are too small to eval- uate the risk of rare complications. 9 –13 Two deaths in Canada from vertebral artery dissec- tion and stroke following chiropractic care in the 1990s attracted much media attention and a call by some neu- rologists to avoid neck manipulation for acute neck pain. 14 There have been many published case reports linking neck manipulation to vertebral artery dissection and stroke. 15 The prevailing theory is that extension and/or rotation of the neck can damage the vertebral artery, particularly within the foramen transversarium at the C1–C2 level. Activities leading to sudden or sus- tained rotation and extension of the neck have been im- plicated, included motor vehicle collision, shoulder checking while driving, sports, lifting, working over- head, falls, sneezing, and coughing. 16 However, most cases of extracranial vertebral arterial dissection are thought to occur spontaneously, and other factors such as connective tissue disorders, migraine, hyper- tension, infection, levels of plasma homocysteine, ves- sel abnormalities, atherosclerosis, central venous
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