From Pages to Practice

By Lisa Caulley, MD, MPH, FRCSC

Published February 21, 2018


Mr. Johnston is a 60-year-old man who presents to your outpatient clinic for preoperative evaluation for a right hip arthroplasty. Determining the appropriate postoperative prophylaxis to prevent venous thromboembolism (VTE) is an important management consideration. Like many people his age, Mr. Johnston has suffered from osteoarthritis for several years. He is otherwise healthy and is not currently taking any medications. He is keen to move forward with surgery, but expresses concern about the risk of “clots” described in online searches as a complication associated with hip arthroplasty. He has been reading about prophylactic therapy but admits he is confused by the many options for anticoagulants in this setting.

Prophylaxis from VTE following total hip and knee arthroplasty has been found to reduce morbidity and mortality. Prior studies have demonstrated the additional benefit of extended postoperative prophylaxis, particularly in patients with total hip arthroplasty. However, the type of VTE prophylaxis and duration of treatment remain unclear. In this week’s NEJM, Anderson et al. compared the safety and efficacy of aspirin and rivaroxaban for postoperative prophylaxis to prevent VTE in the EPCAT II (Extended Venous Thromboembolism Prophylaxis Comparing Rivaroxaban to Aspirin Following Total Hip and Knee Arthroplasty) trial.

In this multicenter, double-blind, randomized-controlled trial, 3424 patients undergoing total hip or knee arthroplasty received rivaroxaban (10 mg once daily for 5 days) post-operatively and then were randomized to continue rivaroxaban (1717 patients) or switch to aspirin (81 mg daily; 1707 patients). Prophylaxis was continued for an additional 9 days after knee arthroplasty and 30 days after hip arthroplasty. Patients who were receiving long-term aspirin therapy before trial entry (855 patients) continued their usual aspirin in addition to the assigned trial medication.

During 90-day follow-up, the rate of symptomatic VTE was 0.64% in the aspirin group and 0.70% in the rivaroxaban group (difference, 0.06 percentage points; 95% CI, −0.55 to 0.66; P<0.001 for noninferiority and P=0.84 for superiority). Major bleeding events occurred in 8 patients in the aspirin group and 5 patients in the rivaroxaban group (difference, 0.18 percentage points; 95% CI, −0.65 to 0.29; P = 0.42). Similarly, rates of clinically important bleeding did not differ significantly between the two groups (difference, 0.30 percentage points; 95% CI, −1.07 to 0.47; P=0.43). Among patients who were receiving long-term aspirin therapy before trial entry, rates of VTE and major bleeding did not differ significantly.

In an accompanying editorial, David Garcia discusses the practice-changing implications of these study findings. He notes that with this relatively inexpensive and user-friendly aspirin-based strategy, “…the EPCAT II trial has established a prophylaxis regimen against which all strategies to prevent venous thromboembolism after joint replacement will be compared.” He highlights the importance of recognizing that these results cannot be extrapolated to very high-risk patients (i.e., patients with a history of VTE, morbid obesity, or cancer) because the trial included relatively few such patients.

The results of the EPCAT II trial provide valuable information about safe prophylactic therapy to prevent VTE after hip and knee arthroplasty, particularly among routine aspirin users. Mr. Johnston can be assured that after an initial 5-day course of rivaroxaban postoperatively, treatment with low-dose aspirin will be as safe and effective as low-dose rivaroxaban for the prevention of symptomatic VTE.

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Lisa is a 2017-2018 NEJM Editorial Fellow. An otolaryngologist-head and neck surgeon by training, she graduated from the University of Toronto Medical School and completed her residency training at the University of Ottawa. She has a Master's in Public Health from the Harvard T. H. Chan School of Public Health.