I read with great interest the commentary by Moira Kapral and Susan Bondy1 on the elegant study by Scott Haldeman and colleagues2 estimating the risk of vertebral artery dissections following chiropractic manipulation. Kapral and Bondy succintly summarized some of the main difficulties that investigators face in attempting to determine the true risk of vertebrobasilar accidents (VBA) following cervical manipulation.
However, I was surprised that Kapral and Bondy claimed that the population-based case–control study from Ontario estimating the risk of stroke from chiropractic manipulation3 “placed the risk of stroke for individuals aged under 45 years at about 1.3 per 100 000 chiropractic visits.” In fact, careful reading of this article demonstrates that it actually stated that “for every 100 000 persons aged < 45 receiving chiropractic, approximately 1.3 cases of VBA attributable to chiropractic would be observed.”
Each chiropractic patient frequently receives a series of visits, and thus it is essential to clearly differentiate between the number of chiropractic patients and the number of chiropractic visits. Careful discrimination between these concepts is especially crucial in this discussion, because the study by Haldeman and colleagues estimates the incidence of stroke following a chiropractic treatment at 1 per 8.06 million chiropractic office visits and 1 per 5.85 million cervical treatments and because Kapral and Bondy seem to imply that these figures are significant underestimates.
William J. Lauretti Chiropractor Bethesda, Md.