Prevention of venous thromboembolism after knee arthroplasty: a randomized, double-blind trial comparing enoxaparin with warfarin

Objective: To compare the effectiveness and safety of fixed-dose enoxaparin and adjusted-dose warfarin in preventing venous thromboembolism after knee arthroplasty. Design: A randomized, double-blind controlled trial. Setting: 8 university hospitals. Patients: 670 consecutive patients who had knee arthroplasty. Intervention: Patients were randomly assigned to receive enoxaparin (30 mg subcutaneously every 12 hours) or adjusted-dose warfarin (international normalized ratio, 2.0 to 3.0). Both regimens were started after surgery. Measurements: The primary end point was the incidence of deep venous thrombosis in patients with adequate bilateral venograms; the secondary end point was hemorrhage. Results: Among the 417 patients with adequate venograms, 109 of 211 warfarin recipients (51.7%) had deep venous thrombosis compared with 76 of 206 enoxaparin recipients (36.9%) (P = 0.003). The absolute risk difference was 14.8% in favor of enoxaparin (95% Cl, 5.3% to 24.1%). Twenty-two warfarin recipients (10.4%) and 24 enoxaparin recipients (11.7%) had proximal venous thrombosis (P > 0.2). The absolute risk difference was 1.2% in favor of warfarin (Cl, -7.2% to 4.8%). The incidence of major bleeding was 1.8% (6 of 334 patients) in the warfarin group and 2.1% (7 of 336 patients) in the enoxaparin group (P > 0.2). The absolute risk difference was 0.3% in favor of warfarin (Cl, -2.4% to 1.8%). Conclusions: A postoperative, fixed-dose enoxaparin regimen is more effective than adjusted-dose warfarin in preventing total deep venous thrombosis after knee arthroplasty. No differences were seen in the incidence of proximal venous thrombosis or clinically overt hemorrhage.
The drug enoxaparin may be more effective than warfarin in preventing the formation of blood clots following surgery to reconstruct the knee. Researchers gave either a fixed dose of enoxaparin or a body weight-adjusted dose of warfarin to 670 patients who had undergone reconstructive knee surgery. Drugs were administered in the postoperative period. Use of enoxaparin was associated with a reduced risk of developing blood clots in the deep veins of the legs, as visualized by x-rays of the legs using radiographic contrast material. Enoxaparin reduced the relative risk of deep vein blood clots by 28.6%, and reduced the absolute risk by 14.8%. A 10% to 12% risk of developing blood clots near the surgical site was noted with use of both enoxaparin and of warfarin.