Comparative Safety of Chiropractic

Chiropractic has an excellent safety record but no healthcare method is completely free of risk. If spinal manipulation were a prescription medica­tion, its rate of major adverse effects would justify calling it remarkably safe. The area of greatest controversy is vertebrobasilar accident (VBA), or stroke. Chiropractic students are taught best practices for recognizing impending strokes, appropriate care and caution are given strong empha­sis, and the profession endorses the use of informed consent.

Full understanding of this issue hinges on the question of whether the rare stroke that occurs following a visit to a chiropractor was actually caused by chiropractic treatment or occurred for reasons not associated with it. Only recently has large-scale, rigorous research addressed this issue, with two large reviews of all records in the Canadian province of Ontario. Because Canada has publicly-funded universal healthcare, this data is presumed to be comprehensive. Questions of a possible causative role for spinal manipulation raised in the first study, by Rothwell et al appear to have been fully resolved in the later Cassidy et al study.

Rothwell Study (Canada, 2001)

Rothwell et al reviewed all records from 1993-1998 and found a total of 582 vertebrobasilar accident cases in the province. Each was age and gender matched to 4 controls from the Ontario population with no history of stroke at the event date. Public health insurance billing records were used to document utilization of chiropractic services during the year prior to VBA onset. Slightly more than 90% had no chiropractic visits in the year preceding their VBA. Of the 57 individuals with VBAs who did visit a chiropractor in the 365 days preceding the VBA (out of 50 million chiro­practic visits during the 5-year period studied), 27 are believed to have had cervical manipulation. Of these, 4 individuals visited a chiropractor on the day immediately preceding the VBA, 5 in the previous 2-7 days, 3 in the previous 8-30 days, and 15 in the previous 31-365 days.

Compared to the controls, there was an increased association of VBA among patients who saw a chiropractor 1-8 days prior to the VBA event, but a decreased association of CVA among patients who saw a chiroprac­tor 8-30 days before the event. Rothwell et al found no association between recent chiropractic visits and VBAs in patients over age 45. However, patients under age 45 were 5 times more likely to have visited a chiropractor within the week prior to the VBA and 5 times more likely to have had 3 or more visits with a cervical diagnosis in the month preceding the VBA. Though Rothwell and colleagues explicitly cautioned against using their data to infer a cause-and-effect relationship between spinal manipulation and stroke, some used their data to make such a connec­tion. There were a total of 6 strokes within 7 days of neck manipulation in the under-45 group, out of approximately 15 million total neck manipula­tions during the time period evaluated.

Cassidy Study (Canada, 2008)

Several years after the Rothwell study, Cassidy and colleagues completed a review of the same Ontario records evaluated by Rothwell’s group and extended the time period covered in the review by three years. They performed additional analyses to determine whether patients who had seen a chiropractor were more likely to have had a stroke than patients who had seen a medical physician. This question, which had not been part of the earlier Rothwell review, was crucial because patients in the early stages of a stroke commonly experience symptoms (headache, neck pain) that may lead them to consult either a chiropractor or a medical doctor.

Cassidy’s group found that it was no more likely for a stroke patient to have seen a chiropractor than a medical physician. In fact, those visiting a medical doctor rather than a chiropractor were more likely to have had a stroke, although this difference was not statistically significant. The authors concluded, “The increased risks of VBA stroke associated with chiropractic and PCP [primary care physician] 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 VB stroke associated chiropractic care compared to primary care.”

Rothwell DM, Bondy SJ, Williams JI. Chiropractic manipulation and stroke: a population-based case-control study. Stroke. May 2001;32(5):1054-1060.
Cassidy JD, Boyle E, Cote P, et al. Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case-control and case-crossover study. Spine. Feb 15 2008;33(4 Suppl):S176-183.