Warfarin for venous thromboembolism prophylaxis after elective hip or knee arthroplasty: exploring the evidence, guidelines, and challenges remaining.

BACKGROUND: Guidelines for the prevention of venous thromboembolism (VTE) after elective total hip or knee arthroplasty (THA/TKA) have been developed separately by the American Academy of Orthopaedic Surgeons (AAOS) and the American College of Chest Physicians (ACCP). Differences exist in approaches to preventing postoperative VTE through prophylaxis.
OBJECTIVE: To compare trials using vitamin K antagonists (VKAs) and differences in guidelines to determine the benefits and drawbacks of warfarin for VTE prophylaxis following THA/TKA. DATA SOURCES: Guidelines from the AAOS published in 2009 and revised in 2011 and from the ACCP published in 2008 were compared for recommendations on the use of VKAs. A MEDLINE search from 1960 to November 2009 was conducted to identify pertinent articles on the use of warfarin or VKAs for VTE prophylaxis following THA/TKA. Search terms included warfarin, vitamin K antagonist, total hip or total knee replacement, and total hip or total knee arthroplasty. STUDY SELECTION AND DATA EXTRACTION: Only clinical trials in which warfarin was the primary agent for prophylaxis compared to other anticoagulants were included. DATA SYNTHESIS: Data on differences between guideline recommendations for the use of VKAs and the importance of a deep vein thrombosis or asymptomatic events were extracted. Thirteen comparative trials using VKAs for VTE prophylaxis and international normalized ratio (INR) targets were assessed. Overall, the incidence of bleeding tended to be lower with the use of VKAs, but thrombosis when including asymptomatic events was numerically higher when comparing INR targets. However, INR targets varied, with no comparative trials assessing the AAOS 2009 recommended INR target of 1.5-2.0. The AAOS guidelines initially recommended a longer duration of therapy and expressed stronger support for the use of aspirin for prophylaxis; however, in 2011, its guidelines were revised, with no specific recommendations as to agent, dose, or INR target goal.
CONCLUSIONS: Warfarin is an effective agent to prevent VTE after elective THA/TKA. The most effective approach, including extended warfarin use up to 4 weeks or longer, has not been determined.