Danish researchers evaluated 37,223 knee replacement patients who had surgery between 1997 and 2007, looking for evidence of post-surgical embolism in the 90-day period following surgery. The authors found 441 patients (1.2%) were hospitalized for blood clots during the 90-day period following knee surgery. Although blood thinners are typically prescribed only during hospitalization, the study suggests that physicians consider extending the duration of blood thinner therapy into the weeks following surgery.

The study also revealed the number of patients admitted to hospitals with clots following knee surgery has increased since 1997, which study author Alma Pedersen, MD, PhD, noted is most likely due to advances in diagnosis which have enabled physicians to identify clots before they cause serious problems. The study also notes that individuals who have a knee replacement surgery due to rheumatoid arthritis have a lower risk of clots than those with other conditions. However, in all patients, the risk can be diminished slightly by replacing only one knee at a time, rather than both.

"Despite the use of blood thinners, patients undergoing knee arthroplasty continue to remain susceptible for clot formation for several weeks following surgery," says Dr. Pedersen. "Future studies should focus on the improvement of prophylaxis following hospital discharge, particularly among elderly patients and those with a history of cardiovascular diseases or previous clot formation."

According to data from the American Thoracic Society, pulmonary embolism is a common complication of hospitalization and contributes to 5% to 10% of deaths in hospitalized patients. Some studies have estimated that more than 1 million Americans experience pulmonary embolisms each year, with 100,000 to 200,000 of these events being fatal.

Dan O'Connor