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 deep venous thrombosis after knee arthroplasty. No differences were seen in the incidence of proximal venous thrombosis or clinically overt hemorrhage.