Published 6/1/2013
Jennie McKee

Aspirin Vs. Warfarin: Which Is Better at Preventing VTE?

Study links aspirin to significantly better outcomes after TJA

Aspirin may be a more effective prophylaxis than warfarin in preventing venous thromboembolism (VTE) after total joint arthroplasty (TJA), according to research presented by Javad Parvizi, MD, FRCS, at the 2013 AAOS Annual Meeting.

When Dr. Parvizi and his colleagues compared the outcomes of primary and revision TJA patients treated with aspirin or warfarin, they found that pulmonary embolism (PE) rates were significantly lower in the TJA patients who received aspirin prophylaxis rather than warfarin prophylaxis. In addition, patients in the aspirin group had a lower rate of deep vein thrombosis (DVT) and fewer problems related to wounds.

Obtaining data
The investigators performed a retrospective, single-center database search and identified 28,923 patients who underwent TJA between January 2000 and June 2012. For 6 weeks following surgery, 2,800 patients (46.8 percent male; mean age, 61.1 years) received 325 mg of aspirin twice daily as a prophylaxis against VTE, while 26,123 patients (42.6 percent male; mean age, 64.3 years) were treated with warfarin, aiming for an International Normalized Ratio (INR) of between 1.5 and 1.8. All patients received the same rehabilitation protocols.

Researchers obtained data on the incidence of PE, DVT, hematoma formation, and other complications for up to 90 days after surgery. The data were evaluated using multivariate analysis and propensity score matching for demographic and comorbid variables.

Measuring the outcomes
Overall, the researchers found that aspirin offered many benefits compared to warfarin. Patients treated with aspirin had an overall PE rate of 0.14 percent compared to the 1.07 percent overall PE rate in patients who received warfarin.

Patients in the aspirin group also had a significantly lower DVT rate of 0.29 percent compared to the DVT rate of 0.99 percent in the warfarin group. In addition, patients who received aspirin had fewer wound-related problems, with a rate of only 0.04 percent, compared to the 0.57 percent rate of wound-related problems in patients in the warfarin group.

The benefits of aspirin also extended to the amount of time patients spent in the hospital. Mean hospital length-of-stay (LOS) for patients in the aspirin group was 2.48 days, while patients treated with warfarin had a mean LOS of 4.08 days.

Dr. Parvizi explained that the median time at which PE occurred in patients receiving warfarin was 2 days postoperatively (range, 1 day to 87 days).

“Of the 280 documented PE cases in patients who received warfarin, 81 percent occurred within the first 3 postoperative days, 89 percent occurred within the first postoperative week, and 94 percent occurred by the end of the second postoperative week,” noted Dr. Parvizi. Other complications, including hematoma and seroma formation, acute infection, and 90-day mortality, did not reach statistical significance in either patient group.

Warfarin: a “drug of the past”?
“For patients receiving warfarin postoperatively, the risk of developing a PE was more than six times as high as the risk of developing a PE while on aspirin,” said Dr. Parvizi, noting that warfarin can be difficult to dose properly because it can interact with food and drugs and can be affected by the patient’s genetic predisposition.

“Warfarin also has a narrow therapeutic index and undergoes hepatic metabolism, making its onset, duration, and offset of action unpredictable,” he said.

Dr. Parvizi acknowledged that the study had several limitations, including disparities in gender, race, and age between the two cohorts. In addition, patients with PE may have been treated at other hospitals and thus would not have been identified in the database as having this complication; however, the PE rates in this study are comparable to those reported in the literature, he noted.

Overall, said Dr. Parvizi, the study’s results suggest that aggressive pharmacologic protocols such as warfarin may increase the risk of postoperative complications.

“The clinical success of less aggressive protocols—mainly aspirin—in conjunction with an increasing number of young, healthy patients who are undergoing hip and knee replacements seems to indicate that selective use of these aggressive pharmacologic protocols is absolutely vital,” he noted, adding that “the cumbersome and unpredictable nature of warfarin for postarthroplasty VTE prevention in healthy patients should make it a drug of the past.”

The results of this retrospective study, asserted Dr. Parvizi, make it clear that prospective trials are needed to define the optimal modalities for preventing VTE.

Dr. Parvizi’s coauthors on “Aspirin: An Alternative for Pulmonary Embolism Prophylaxis Following Arthroplasty” include Ibrahim J. Raphael, MD; Eric H. Tischler, BA; Ronald Huang, MD; Richard H. Rothman, MD, PhD; and William J. Hozack, MD.

Disclosure information: Dr. Parvizi—Cadence; 3M; Ceramtec; Pfizer; Salient Surgical; Smith & Nephew; TissueGene; Zimmer; Baxter; DePuy, A Johnson & Johnson Company; Musculoskeletal Transplant Foundation; National Institutes of Health (NIAMS & NICHD); Stryker; Zimmer; Jaypee; Journal of Arthroplasty; Journal of Bone and Joint Surgery (JBJS)–American; Saunders/Mosby-Elsevier; SLACK Incorporated; Wolters Kluwer Health - Lippincott Williams & Wilkins; American Journal of Orthopedics; Current Opinion in Orthopaedics; International Orthopaedics; JBJS–British; Journal of the American Academy of Orthopaedic Surgeons; Magnifi Group; Orthopedics Today; SmartTech; United Healthcare. Mr. Tischler, and Drs. Raphael and Huang—no conflicts. Dr. Rothman—Stryker; Journal of Arthroplasty. Dr. Hozack—Stryker; Journal of Arthroplasty; Hip Society.

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org

Bottom Line

  • This retrospective, single-center database review found that TJA patients treated with aspirin had a lower rate of PE and DVT, fewer wound-related problems, and a shorter hospital stay than those treated with warfarin.
  • Most cases (81 percent) of PE in patients treated with warfarin occurred within the first 3 days after surgery.
  • Warfarin can be difficult to dose properly because it can interact with food and drugs and can be affected by the patient’s genetic predisposition.
  • Selective use of aggressive pharmocologic protocols may be advisable for younger, healthier patients undergoing TJA.