Share this article on:

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

Cassidy, J David DC, PhD, DrMedSc*†‡; Boyle, Eleanor PhD*; Côté, Pierre DC, PhD*†‡§; He, Yaohua MD, PhD*; Hogg-Johnson, Sheilah PhD†§; Silver, Frank L. MD, FRCPC¶∥; Bondy, Susan J. PhD

doi: 10.1097/BRS.0b013e3181644600
Supplementary Research Studies

Study Design. Population-based, case-control and case-crossover study.

Objective. To investigate associations between chiropractic 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 headache 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 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 seeking care before their stroke. We found no evidence of excess risk of VBA stroke associated chiropractic care compared to primary care.

We estimated the association between chiropractic visits, primary care physician visits and vertebrobasilar artery (VBA) stroke. In those < 45 years, the risk of VBA stroke was elevated after visiting a chiropractor or primary care physician. This is likely explained by patients seeking care for symptoms of vertebral artery dissection before stroke.

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 Evaluation, University of Toronto, Toronto, ON, Canada; §Institute for Work & Health, Toronto, ON, Canada; ¶University Health Network Stroke Program, Toronto Western Hospital, Toronto, ON, Canada; and ∥Division of Neurology, Department of Medicine, Faculty 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, Canada M5T 2S8; E-mail:

© 2008 Lippincott Williams & Wilkins, Inc.