May 12, 2003 -- If you've got a pain in the neck, think twice about getting your neck cracked. Spinal manipulative therapy, as chiropractors call it, increases your risk of stroke.

The overall risk is probably very small. But the link between stroke and neck cracking is real, says neurologist Wade S. Smith, MD, PhD, director of the neurovascular service at the University of California, San Francisco.

"Some neurologists think chiropractors are causing a lot of strokes, but we think it is a very low risk," Smith tells WebMD. "I don't think it is so low that a patient doesn't need to be informed about it. The consequences of a stroke can be enormous. People should be aware that spinal manipulation increases risk of stroke. Anybody who does a procedure of any kind that carries a risk should tell their patients about that risk."

One of the leading causes of stroke before age 45 is something called cervical arterial dissection. That's when one of the two arteries that wind through the back of the neck to the brain starts to tear. The lining of the artery bleeds and forms a blood clot. This clot can easily enter the brain and cause a fatal stroke.

Earlier studies in Canada compared stroke registries with medical records. Strokes in younger adults were strongly associated with seeing a chiropractor. Was there a real cause-and-effect connection? Smith looked for more evidence.

His team looked at all patients under the age of 60 who from 1995-2000 visited two large medical centers for cervical dissections resulting in strokes or the passing stroke-like episodes called transient ischemic attacks. They found 151 such patients; 51 were available for study. The patients were compared with 100 age-matched patients whose strokes were not due to arterial dissection. All were asked a battery of questions -- including whether they had head or neck pain in the 30 days before their stroke, and whether they got a spinal manipulation during that time.

Of the 51 patients, seven (14%) remembered getting their necks cracked before their stroke. Only 3% of the control patients remembered seeing a chiropractor in the month before their stroke. After controlling for all other factors, getting a spinal adjustment upped the risk of stroke 6.62-fold.