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Knee, Hip Replacements Carry Blood Clot Risk

Study: About 1 in 100 Knee Replacement Patients Will Develop a Blood Clot Before Leaving the Hospital
By
WebMD Health News
Reviewed by Laura J. Martin, MD

Jan. 17, 2012 -- Doctors have long known that dangerous blood clots can occur after joint replacement surgery of the knees or hips.

Now, a new analysis puts numbers on the risk.

About 1 in 100 patients who undergo knee replacement surgery and 1 in 200 patients who have hip replacement surgery will develop a blood clot called venous thromboembolism before leaving the hospital. 

"Actual rates in hospitals might indeed be higher," says researcher Jean-Marie Januel, PhD, MPH, RN, senior researcher at the Institute of Social and Preventive Medicine at the University Hospital of Lausanne in Switzerland. The new figures were estimates after Januel and his team evaluated the results of 47 published studies on blood clot risks after joint replacement surgery.

"Actual rates in hospitals should be monitored and made available to patients," Januel tells WebMD.

The new report is published in the Journal of the American Medical Association.

The new estimates may not reflect the true risk of blood clots, according to two doctors familiar with the new analysis. That is because the blood clot risk persists beyond the study period, they tell WebMD.

Orthopaedic Surgery and Blood Clot Risk

Knee replacement surgery and hip replacement surgery are done to repair arthritic or injured joints. The number of these surgeries has increased in recent years. The surgeries are also being done on younger patients.

About 230,000 hip replacement surgeries were done in 2007, according to the CDC. More than 600,000 knee replacement surgeries were done in 2009, according to the Agency for Healthcare Research and Quality. Blood clots after the surgeries can occur in the deep veins of the legs or elsewhere. They often occur without symptoms. Some of these clots can travel to the lungs.

Doctors routinely prescribe anti-clotting drugs for the patients to help prevent blood clots from forming after the surgical procedure. However, they cannot prevent all clots.

Risk of Blood Clots After Hip, Knee Surgery

Januel's team researched the medical literature to find studies that assessed the risk of blood clots after knee replacement or hip replacement surgery. They focused on studies that looked at clots that occurred before leaving the hospital.

They evaluated the results of 47 studies. Most were clinical trials. Of the 47, 21 studies included patients having hip replacement, 20 included those having knee replacement, and six included both. The studies included nearly 45,000 patients.

One unexpected finding: the risk of deep vein clots was higher after knee replacement than hip, the researchers say. Other studies have found that the clots are more common after hip surgery when the period after the hospital stay is included.

Risk of Blood Clots ‘Extends Beyond the Hospital Stay’

The estimates may not be accurate for a number of reasons, says John A. Heit, MD, professor of medicine and a cardiologist at Mayo Clinic in Rochester, Minn. He wrote an editorial to accompany the study.

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