(Reuters) – Older patients who have a hip or knee replaced face an increased risk of heart attack in the two weeks after the procedure, according to an international study.

Researchers, whose findings appeared in the Archives of Internal Medicine, said that people having joint surgery had up to 31 times the risk of a heart attack shortly afterward.

“The risk of acute myocardial infarction is substantially increased in the first 2 weeks after total hip replacement (25-fold) and total knee replacement surgery (31-fold) compared with controls,” wrote Arief Lalmohamed from Utrecht University in the Netherlands, who led the study.

The link between joint surgeries and heart problems was especially high for patients aged 80 or older, they found. But those under the age of 60 weren’t at any higher risk.

Although it’s not clear that the hip and knee procedures themselves triggered the heart attacks, researchers said it’s reasonable to think they would have some role.

“Surgery is a risk, because surgery and anesthesia that you need to have the surgery increase stress levels for patients,” said William Hozack, an orthopedic surgeon at the Rothman Institute in Philadelphia, who wasn’t involved in the study.

The findings come from hospital records for 95,000 people who had a hip or knee replaced in Denmark between 1998 and 2007. The researchers compared each patient with three people, of the same age and gender, who didn’t have a joint replaced.

Over the six weeks after their surgeries, one in 200 patients who had a hip replaced and one in 500 who underwent knee replacement had a heart attack.

The researchers couldn’t account for everything about patients that might affect both their risk of needing a joint replaced and having a heart attack, such as being overweight or obese, or having high blood pressure.

Lalmohamed expects the procedures do have some direct impact on heart risk. Cutting into bones could promote clot formation in the bone marrow, especially in hip surgery, his team said.

Blood loss and oxygen deprivation can also happen during any major surgery, he told Reuters Health.

“These stressors are known to increase the risk of heart attack. Furthermore, the perioperative period itself is a very stressful time for the patient,” he said, adding that patients should discuss their heart history with their doctor before surgery. SOURCE: bit.ly/MbBLbb

(Reporting from New York by Genevra Pittman at Reuters Health; Editing by Elaine Lies and Michael Perry)