BOSTON -- Before your next trip to the chiropractor there's a warning from three of Boston's top neurologists.

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NewsCenter 5's Heather Unruh reported that while most chiropractic care is perfectly safe, there is one adjustment to the neck they say carries a small but potentially serious risk.

Darlene suffered a stroke caused by a tear in her vertebral artery in the back of her neck. She was just 34. It was a red flag for doctors who immediately wanted to know if she'd been treated recently by a chiropractor.

"Chiropractic neck manipulation is only one type of injury that can produce this pattern, and I would say that we see this uncommonly, but often enough that it's one of the first questions we ask when we see a young patient with a stroke," Massachusetts General Hospital Dr. Lee Schwamm said.

Schwamm said that he sees one to two cases a year, and top neurologists at two other Boston hospitals warn they're also concerned.

"It's a small risk, but my feeling is that people should know there's a risk," Beth Israel Deaconess Medical Center Dr. Lou Caplan said.

Documentation is growing. A new study in the journal Neurology found a "strong relationship" between spinal manipulation and artery tears. How high is the risk? No one really knows.

"I accept that we don't know how risky it is. I know they don't know how risky it is either," Tufts New England Medical Center's Dr. David Thaler said.

It's about as risky as stargazing, according to Dr. Anthony Rosner, who studies the issue for the American Chiropractic Association.

"We hear stories of people who were driving, you know, turn their heads, tennis matches, things like this. Yes, you know, it may happen in the chiropractor's office. It could happen a number of places," Rosner said.

Legally, chiropractors aren't required to warn patients, but some do.

"You should explain the possible side effects associated with cervical manipulation, whether they're documented or not," Dr. Ian Paskowski said.

In court, Darlene couldn't prove what caused her stroke.

"He might have helped it along. He did a good job helping it along though didn't he," Darlene said.

"People come to the chiropractors complaining of neck pain. So the question is, did they cause an accident or something in the manipulation? And you have to ask yourself was something in progress?" Rosner said.

While insisting it's safe, some chiropractors have altered their practice, and no longer do the full neck rotation.

"With that slight potential, I prefer not to use the procedure that might put the patient at risk," Dr. Matthew Kowalski said.

The neurologists NewsCenter 5 spoke to say most chiropractic care involves little to no risk, but if you choose neck manipulation, ask about the risk of stroke.

"And if the chiropractor says, 'No, there's not,' I tell my patients to leave the chiropractor's office because they're lying," Thaler said.