Here's and interesting artical I found that I think neatly sums up the current position on this:

CHIROPRACTIC AND STROKE - THE EVIDENCE

The following information addresses the often exaggerated concern that chiropractic adjustments cause cerebrovascular accidents (stroke). Putting it plainly, there is no link, it is a red herring and perhaps is quite the opposite.

Chiropractic is one of the safest forms of healthcare in the world and is at the forefront of spinal care and the wellness movement.

Unfortunately there have been many unethical and anti-competitive attempts to discredit chiropractic (refs 1-3) which is the largest drugless health care profession in the world, and one of the fastest growing.(4)

A suggestion has been mooted which cannot be proved or disproved that chiropractic might be associated with stroke (not linked to or causing but associated – confused? Read on), one study showing showed that stroke occurred a short time after 1 in 5.85 million chiropractic neck interventions. One in almost six million?? Huh? How many strokes occur after a cup of tea? Or even any other daily activity – what about looking up? Straining to go to the toilet? What constitutes an association?

To create a study capable of proving or disproving an association or not, you would have to adjust 6 million people with a higher than average risk of stroke to see if one of them had an event related to that adjustment. To prove or disprove a link, a study would have to involve 600 million people to get a study group of perhaps 100 adjustment related strokes. This is an impossibility and the reason why such a red herring has continued to exist.

On examination, many of the strokes quoted in the literature have been falsely attributed to chiropractors when in fact the person carrying out the manipulation was not a trained chiropractor (examples include a kung fu practitioner, a blind masseur, someone’s wife, an Indian barber, GPs, osteopaths, and physiotherapists).(5)

In a German study published in Neurology in 2006, an attempt was again made to link chiropractic and stroke when in fact none of those adjustments/ manipulations were carried out by chiropractors.(6) Half of the manipulations (not skilled chiropractic adjustments) that resulted in stroke were carried out by orthopaedic surgeons the other half by untrained unqualified heilopraktkers masquerading as ‘chiro-practitioners.’

The point here should have been public protection, the safety record of manipulation by chiropractors and the need for legislation to protect both the public and the profession instead it was used to libel a profession. Indeed these same incidents in Germany were brought to public attention by a chiropractic researcher, Dr. Adrian Wenban, in such a vein at the 2005 European Chiropractic Convention, a full year previous to its publication in Neurology.(6)

In over thirty years involving billions of chiropractic adjustments in the US, there were ten cases of death within any sort of period of time that followed neck manipulation. Nine of these were carried out by medical doctors, even though chiropractors perform 94% of the cervical manipulations/ adjustments in America. In other words, medical manipulators caused 90% of the lethal complications in less than 6% of all those being manipulated, which sends out a strong message for the quality of care and safety of chiropractic.(7)

Sorry now hold on; it follows then that if the figure of association was one in six million for neck manipulation that figure now looks more like one in 60 million for chiropractic adjustments. The study group then needed to prove or disprove it? Yes that’s right, it would require six billion people all at a higher than average risk of stroke being adjusted and monitored pre and post adjustment for twenty four to forty eights hours after and then all that information collated, collaborated and reviewed – now you can see why it can neither be proved nor disproved. It is a red herring.

Put into perspective, what are the risks for every day activities and medication promoted everyday? Reversing the car, jogging, taking HRT, blood pressure medication, cholesterol lowering medication, even taking a neurofen, a pain killer or an anti-inflammatory instead of being adjusted?

Even if we were to agree this estimate of association of one in six million, this is over 700 times lower than the established risk of death from taking anti-inflammatories such as aspirin and ibuprofen, yet these are prescribed everyday for head, neck and back pain. The figure of association is also much less than that associated with many everyday activities including reversing a car, jogging, tai chi, various sleeping positions, coughing, stooping to get a bucket and even yawning.(8-10) Yes you are more likely to die from yawning than a chiropractic adjustment. Now do you see it?

In 2002, researchers announced they were calling a halt to a study after it had become clear that the risks of HRT, including stroke, outweighed its benefits. The study results, which appeared in the July 17, 2002 issue of the Journal of the American Medical Association, were released early because of the importance of the researchers' findings. (11) HRT is still being prescribed, long term, despite this.

There is interestingly enough evidence to show those being adjusted are less likely to have a stroke. When you compare estimates of the risk of stroke following neck adjustment/ manipulation (using the higher estimate of 0.00025%) to the risk of fatal stroke occurring in the general U.S. population (0.00057%) it is less than half.(12-16) There is also ample proof to show people adjusted regularly clearly benefit from regular chiropractic care and enjoy a higher level of health, mobility and an improved quality of life.

There is no link. An association has been mooted that cannot be either proved or disproved in an effort to smear the chiropractic profession in the public arena; a profession that has a high safety record and offers a choice for better health without the use of drugs or surgery. It is a red herring: neither proveable nor disproveable. What is alarming and is real is the risk of stroke from the very medications often given instead of being referred to a chiropractor.

Chiropractic does not cause stroke, it is not linked with stroke nor is it associated with stroke. Chiropractic is however linked with better health, a high safety record and established benefit.

References

1. Wilk CA. Medicine, monopolies, and malice. Garden City Park, NY: Avery Publishing Group; 1996. (renamed Chiropractic and Medicine: The Need to Work Together for Effectiveness)

2. Canadian Stroke Consortium

3. www.quackwatch.com and www.chirobase.com

4. Eisenberg DM, Davis RB, Ettner SL, Appel S, Wilkey S, Van Rompay M, Kessler RC. Trends in alternative medicine use in the United States, 1990-1997. Journal of the American Medical Association 1998; 280(18): 1569-1575.

5. Terrett AGJ. Misuse of the literature by medical authors in discussing spinal manipulative therapy injury. Journal of Manipulative and Physiological Therapeutics 1995;18(4): 203-10.

6. Vertebral artery dissections after chiropractic neck manipulation in Germany over three years. Reuter U, Hamling M, Kavuk I, Einhaupl KM, Schielke E; J Neurol. 2006 Jun;253(6):724-730.

7. http://www.chiroweb.com/archives/17/05/05.html

8. Dabbs V, Lauretti W. A risk assessment of cervical manipulation vs NSAIDs for the treatment of neck pain. Journal of Manipulative and Physiological Therapeutics 1995; 18(8): 530-536.

9. Wolfe MM, Lichtenstein DR, Singh G. Gastrointestinal toxicity of non-steroidal anti-inflammatory drugs. New England Journal of Medicine 1999; 340(24): 1888-99.

10. Graumlich JF. Preventing gastrointestinal complications of NSAIDs: Risk factors, recent advances, and latest strategies. Postgrad Med 2001; 109(5): 117-28.

11. Risks and Benefits of Estrogen Plus Progestin in Healthy Postmenopausal Women. Principal Results From the Women's Health Initiative Randomized Controlled Trial. Journal of the American Medical Association. 2002;288:321-333.

12. Myler L: Letter to the editor. Journal of Manipulative and Physiological Therapeutics 1996;19: 357.

13. Cohn A. A review of the literature regarding stroke and chiropractic. Journal Of Vertebral Subluxation Research 2001;4(3):42-59.)

14. Shievink WT, Mokri, B, O'Fallon WM. Recurrent spontaneous cervical-artery dissection. New England Journal of Medicine 1994; 330: 393-397.

15. Shievink WT, Mokri B, Whisnant JP. Internal carotid artery dissection in a community: Rochester, Minnesota, 1987-1992. Stroke 1993; 24: 1678-1680.

16. Giroud M, Fayolle H, Andre N, Dumas R, Becker F, Martin D, Baudoin N, Krause D. Incidence of internal carotid artery dissection in the community of Dijon [Letter]. Journal of Neurology and Neurosurgical Psychiatry 1994; 57: 1443.