People who have undergone a hip replacement surgery have a four-fold increased risk of having a stroke, especially in the first two weeks after the surgery.

Researchers found that risk of ischemic stroke caused by artery blockage increases nearly 4.7-fold, and hemorrhagic stroke caused by bleeding in the brain 4.4-fold.

"This is the first study to evaluate the risk of stroke in patients undergoing total hip replacement compared to people in the general population who did not undergo the surgery, but were matched for age, sex and geographical region," said Frank de Vries, Ph.D., assistant professor of pharmacoepidemiology at Utrecht University in the Netherlands and lead author of the study.

Researchers said that each year about 1 million hip replacement surgeries are performed around the world, with about 300,000 in the U.S.

"It makes sense to evaluate the risk of stroke two weeks after surgery. There is an increasing tendency to decrease the length of hospital stay because of improved therapy and because of strategies to reduce costs and mobilize patients as soon as possible," de Vries said.

The study included 66,583 patients from Denmark who had undergone total hip replacement. Researchers compared these patients' stroke risk to the risk of stroke in 199,995 people who hadn't undergone the surgery.

The study found that for the first six weeks after the surgery the risk of an ischemic stroke remained high while the risk for a hemorrhagic stroke remained high for as long as 12 weeks.

"Up to one year following surgery, there is diminishing risk of stroke after six to 12 weeks. At one year, the stroke risk is comparable to those who did not undergo surgery," de Vries said.

The study is published in the journal Stroke.