The Incidence of Symptomatic Venous Thromboembolism During and After Prophylaxis With Enoxaparin: A Multi-institutional Cohort Study of Patients Who Underwent Hip or Knee Arthroplasty

BACKGROUND: Despite low molecular weight heparin prophylaxis, the incidence of venographically detected, residual deep vein thrombosis after hip and knee arthroplasty remains high, at approximately 15% and 30%, respectively. Most of these thrombi are asymptomatic and of unknown clinical significance. Nevertheless, because they have the potential to grow, limiting prophylaxis to the in-hospital period may provide inadequate protection. METHODS: We studied a cohort of 1984 consecutive patients who had hip or knee arthroplasty at 1 of 28 participating hospitals. Patients received enoxaparin prophylaxis, 30 mg subcutaneously every 12 hours for up to 14 days, and underwent predischarge compression ultrasonography. Study end points were symptomatic deep vein thrombosis or pulmonary embolism during and after prophylaxis, asymptomatic venous thrombosis detected by predischarge compression ultrasonography, and major hemorrhage. The duration of follow-up was 84 days. RESULTS: Enoxaparin treatment was started a mean (+/- SD) of 17.9 +/- 10.4 hours after the completion of surgery and was given for a mean of 18.0 +/- 6.9 doses. Eighty-two patients (4.1%; 95% confidence interval, 3.3%-5.0%) developed venous thromboembolism. The rates of thromboembolic events during and after prophylaxis were 2.1% and 2.0%, respectively. Only 3 patients (0.15%) had abnormal predischarge compression ultrasonography. Three patients (0.15%) died of pulmonary embolism. Major hemorrhage occurred in 58 patients (2.9%; 95% confidence interval, 2.2%-3.7%). CONCLUSIONS: Postoperative prophylaxis with enoxaparin for a mean of 9 days is associated with a clinically acceptable rate of symptomatic venous thromboembolism and major hemorrhage. Predischarge compression ultrasonography cannot be justified.