LETTER
Prevention of Venous Thrombosis in Knee Arthroplasty
Michael Jacobson, MD, MPH
15 January 1997 | Volume 126 Issue 2 | Page 173
TO THE EDITOR:
In a randomized trial [1], Leclerc and colleagues compared postoperative, fixed-dose enoxaparin (a low-molecular-weight heparin) with adjusted-dose warfarin for the prevention of venous thromboembolism after knee arthroplasty. Enoxaparin was more effective in preventing deep venous thrombosis, as detected by venography. However, no statistically significant difference was seen between the two treatments in the incidence of proximal deep venous thrombosis or major bleeding.
The study design was biased in favor of enoxaparin. Therapy with oral warfarin was begun on the evening after surgery; therapy with subcutaneous enoxaparin was started on the morning after. Although low-molecular-weight heparin therapy was initiated some 12 hours later than warfarin, the normal delay in onset of warfarin action is such that the drug would not become therapeutic until well after enoxaparin had reached effective levels.
After knee arthroplasty, one would expect deep venous thrombosis to begin in the calf veins and develop proximally. The fact that the benefit of enoxaparin was limited to calf-vein thrombosis supports the hypothesis that enoxaparin's advantage was due to its earlier onset of action and not to an inherent superiority.
A less-biased study design might have compared enoxaparin alone with warfarin plus a short course of subcutaneous heparin therapy (to "cover" the early postoperative period).
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Author and Article Information
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Lenox Hill Hospital, New York, NY 10021
1. Leclerc JR, Geerts WH, Desjardins L, Laflamme GH, l'Esperance B, Demers C, et al. Prevention of venous thromboembolism after knee arthroplasty. A randomized, double-blind trial comparing enoxaparin with warfarin. Ann Intern Med. 1996; 124:619-26.
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