Re: Chiropractic Manipulation and Stroke
Anthony L. Rosner, PhD
To the Editor:
The study of Rothwell et al, recently published in Stroke,  attempts to add some light to the considerable heat generated by a long series of case studies,  some of which have implied that spinal manipulation is exceedingly dangerous, suggesting that "patients, chiropractors, and physicians should be aware of the potential adverse neurologic outcomes following chiropractic adjustment"  or (even worse) "since possible complications cannot be predicted and may be very severe, it seems of utmost importance to carefully evaluate the benefit-risk ratio of each cervical manipulation."  By adding a control patient population that did not report a vertebrobasilar accident (VBA) stroke but saw a chiropractor nevertheless, Rothwell and colleagues have attempted to clarify whether a visit to a chiropractor constitutes a significant risk factor leading to a VBA. Their design represents an improvement over the previous simplistic and largely undocumented recollections of patients and therapists attempting to attribute VBAs directly to cervical manipulations.
Unfortunately, the authors miss the point. Comparing stroke with nonstroke patients visiting the chiropractor begs the question; the fact remains that the vast preponderance of VBA stroke victims most likely never visited the chiropractors office before the vascular event in the first place. No less than 68 everyday activities have been implicated in disrupting cerebral circulation.  Among these activities, 18 (including childbirth, overhead work, turning the head while driving a vehicle, swimming, and beauty parlor events) have actually been associated with vascular accidents but are decidedly nonmanipulative. 
Assuming that VBAs are the result of blunt trauma may actually exonerate most cervical adjustments as a causative agent. Peak elongations of the vertebral artery during neck manipulative treatments have recently been shown to be at most approximately 11% of the elongations observed at the arterial failure limit; in fact, these elongations are consistently lower than those seen during routine range of motion and diagnostic testing.  What is becoming more and more apparent is that VBAs must be considered the result of cumulative events over an extended period of time rather than recent visits to the chiropractor.
In concrete terms, this would suggest that a subset of stroke patients who had sought chiropractic treatment for neck pain were already well on the way to experiencing a VBA accident. The study of Rothwell et al omitted the most obvious and convincing control group, which would have been a cohort of patients with neck pain seeking treatment by practitioners other than chiropractors, such as allopathic physicians. This would have more directly reflected the development of VBAs and avoided the highly conjectural attempt to lay the blame directly to chiropractic manipulation, as has been done in the studies of inferior design cited earlier. 
As shown in their Table 1, the entire argument as to whether spinal manipulation is a significant risk factor appears to hinge on a total of 5 cases over 5 years, or 1 case per year. To put this matter in the proper perspective, one should be forever cognizant of the fact that death rates following cervical manipulation calculate to be anywhere between 1/100 to 1/400 the rates seen in the use of NSAIDs for similar conditions. [11, 12] Death rates from lumbar spine operations have been reported to be 300 times higher than those produced by cerebrovascular accidents in spinal manipulation. [13, 14] For cervical surgeries, recent death rates have been estimated to be 700-fold greater.  As Rome  has pointed out, risks for "virtually all" medical procedures ranging from the taking of blood samples  or use of vitamins or drugs  are routinely accepted by the public as a matter of course.
Until these lifestyle risks are properly bundled into a study of the proper design, the public will continue to be misled by studies that appear to have magnified out of proportion the extremely low but admittedly problematic risk of cervical manipulation. One would hope that future studies would maintain a more balanced perspective on the likely causes of VBA and not miss the forest for the trees.
- Rothwell DM, Bondy SJ, Williams JI. Chiropractic manipulation and stroke: a population-based case-control study. Stroke. 2001; 32: 10541060.
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