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Don’t discount aspirin for DVT prevention

New study finds common drug a possible treatment option to prevent blood clots in knee replacement patients

Taking aspirin to prevent blood clots after knee surgery may be a safe and effective alternative to currently recommended treatments that are often costlier and riskier, according to preliminary results from a study presented at the 2008 Annual Meeting by Kevin J. Bozic, MD, MBA. The study found that patients taking aspirin had less risk of developing blood clots than patients taking other blood-thinning drugs. They also faced a similar risk compared to patients receiving injectable drugs.

“Given the modern, less invasive techniques that orthopaedic surgeons are using now for total knee replacement, aspirin should be reconsidered as a viable alternative to recommended therapies,” said Dr. Bozic.

Although current clinical practice guidelines for preventing deep venous thromboembolism (DVT) after total knee replacement do not recommend aspirin use, this study suggests otherwise.

Kevin J. Bozic,
MD, MBA

Dr. Bozic and his team compared data from more than 93,840 patients who underwent knee replacement surgeries at 300 hospitals between October 2003 and September 2005. Researchers compared the risk of blood clots, mortality, surgical-site bleeding, and infection in patients who received aspirin and those who were given guideline-approved therapies.

The study found that patients taking aspirin had fewer risk factors for blood clots prior to surgery and lower odds for blood clots compared to patients on warfarin. The risk of blood clots in patients taking aspirin was similar to that in patients receiving injectable therapies to prevent clots. No difference was found in either bleeding risks or mortality.

“Not only have surgical techniques changed, but patients undergoing knee surgery today are more likely to be younger and healthier than when the current treatment guidelines were developed,” said Dr. Bozic. “Aspirin is a simple, inexpensive, and commonly used drug with few side effects, so it’s a very attractive alternative.”

The study concludes that more research needs to be conducted to help physicians determine which patient characteristics and treatment factors are best suited for aspirin use to prevent blood clots in knee replacement patients.

Most patients who undergo total knee replacement are between the ages of 60 and 80, but orthopaedic surgeons evaluate patients on an individual basis. Recommendations for surgery are based on a patient’s pain and disability, not age. Total knee replacements have been performed successfully at all ages, from teenagers with juvenile arthritis to elderly patients with degenerative arthritis. This study is significant, because more than 533,000 knee replacements were performed in 2005.

Co-authors of Scientific Paper 073, “Is there a role for aspirin in venous thromboembolism prophylaxis following total knee replacement?” are Andrew Auerbach, MD, MPH; Judy Maselli, BA; and Thomas Parker Vail, MD.

Disclosure: Dr. Bozic and his co-authors received research grants from the Orthopaedic Research and Education Foundation and California Healthcare Foundation, and the Patient Safety Research and Training Grant from the Agency for Healthcare Research and Quality.

AAOS weighs in with clinical guidelines
In 2007, AAOS published clinical guidelines on the prevention of symptomatic pulmonary embolism (PE) in patients undergoing total joint arthroplasty. These evidence-based guidelines differed from previously published guidelines on the prevention of venous thromboembolism developed by the American College of Chest Physicians.

The AAOS clinical guidelines on the prevention of symptomatic PE in patients undergoing total joint arthroplasty allow the physician to assign a patient to one of four risk categories, based on the risk of PE and major bleeding.

The suggestions for prophylaxis differ in each of the four categories, but are all in concert with the guidelines promoted by the Surgical Care Improvement Project (SCIP). The AAOS guidelines suggest that mechanical prophylaxis should be used in all patients. In addition, warfarin is an alternative in all four categories.

If the physician documents that the patient is above standard risk for major bleeding, regardless of the patient’s risk for PE, prophylactic options include warfarin, aspirin, or nothing except mechanical prophylaxis. This is compatible with the SCIP guidelines, which state that if the patient is at high risk for bleeding, the use of mechanical prophylaxis only is acceptable.

The AAOS clinical guidelines are available online at www.aaos.org/guidelines

AAOS Now
April 2008 Issue
http://www.aaos.org/news/aaosnow/apr08/clinical1.asp