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Arthritis Health Center

Knee, Hip Replacements Carry Blood Clot Risk

Study: About 1 in 100 Knee Replacement Patients Will Develop a Blood Clot Before Leaving the Hospital
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Risk of Blood Clots After Hip, Knee Surgery continued...

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.

"They are missing a lot of people who have clots," he says.

Their estimates may be on target for just the hospitalization period, he says. However, because the risk for clots persists much longer, depending on the surgery, the estimates of overall clot risk may be off, he says.

Citing several published studies, Heit says the risk period for clots in the deep veins, for instance, can be up to 12 weeks after hip replacement and up to six weeks after knee surgery.

These long-term risks are the most important for patients to know about, he says.

About 80% of the patients in the studies analyzed were in clinical trials, he says, noting that those patients may differ in important ways from other patients.

"The real risk extends beyond the hospital stay," says Bert Thomas, MD, attending surgeon and chief of the joint replacement service at Santa Monica-UCLA Medical Center & Orthopaedic Hospital. He is also a professor and division chief of the joint replacement service at the University of California Los Angeles David Geffen School of Medicine.

"So we recommend preventive anti-clotting medicine continue for six weeks," Thomas tells WebMD.  "Some doctors think it should go longer."

However, he says, the anti-clotting medicines themselves carry risks, such as bleeding.

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