Clinical Question

Is aspirin as effective as enoxaparin for preventing symptomatic venous thromboembolism (VTE) after total hip or knee arthroplasty?

Bottom Line

The study showed superiority of enoxaparin over aspirin for VTE prophylaxis after total hip or knee arthroplasty. This contrasts with a previous study that showed noninferiority of aspirin compared with rivaroxaban (Xarelto). In that study, all patients received five days of rivaroxaban before randomization. The primary outcome focused on proximal deep venous thrombosis (DVT) or pulmonary embolism, which may be more clinically important than the distal DVTs that drove the difference in the current study. (Level of Evidence = 1b)

Synopsis

In the cluster-randomized crossover study from Australia, the investigators randomized 31 hospitals to administer aspirin, 100 mg daily, or subcutaneous enoxaparin, 40 mg daily, as VTE prophylaxis following total hip or knee arthroplasty for osteoarthritis. The duration of treatment was 35 days after hip arthroplasty and 14 days after knee arthroplasty. Approximately 15% of patients in both groups who were already taking aspirin preoperatively continued treatment, although the dose was adjusted to the dose used in the aspirin group. Of the 31 hospitals, 16 enrolled patients for the other treatment group once they achieved the patient enrollment target. In the final analysis, investigators included 5,416 patients from 21 hospitals in the aspirin group and 3,787 patients from 20 hospitals in the enoxaparin group. The two groups had similar baseline characteristics. The primary outcome of symptomatic VTE within 90 days occurred in 3.45% of the aspirin group and 1.82% of the enoxaparin group (estimated difference = 1.97%; 95% CI, 0.54% to 3.41%). This did not meet the pre-specified noninferiority criteria for aspirin but did meet statistical superiority for enoxaparin compared with aspirin (P = .07). This difference was driven by a significantly higher number of below-knee DVTs in the aspirin group (2.4% vs. 1.2%; P = .004). Although no significant differences were detected in pulmonary embolisms or above-knee DVTs, the study was not adequately powered to detect differences for these individual outcomes. The two groups did not differ in secondary outcomes, including death and major bleeding.