Enoxaparin better than aspirin for prevention of venous thromboembolism after total hip or knee arthroplasty

Reference

CRISTAL Study Group, Sidhu VS, Kelly TL, et al. Effect of aspirin vs enoxaparin on symptomatic venous thromboembolism in patients undergoing hip or knee arthroplasty. JAMA 2022;328(8):719-727.

Synopsis

In this cluster-randomized crossover study from Australia, the investigators randomized 31 hospitals to administer either aspirin 100 mg daily or subcutaneous enoxaparin 40 mg daily as venous thromboembolism (VTE) prophylaxis following total hip arthroplasty (THA) or total knee arthroplasty (TKA) for osteoarthritis. The duration of treatment was 35 days following THA and 14 days following TKA. The 15% of patients in both groups who were already taking aspirin preoperatively continued this treatment, although the dose was adjusted to the study dose in the aspirin group. Of the 31 hospitals, 16 hospitals crossed over to the other treatment once they achieved the patient enrollment target for the first group. In the final analysis, investigators included 5416 patients from 21 hospitals in the aspirin group and 3787 patients from 20 hospitals in the enoxaparin group. The 2 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% - 3.41%). This did not meet the prespecified 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 deep venous thromboses (DVTs) in the aspirin group (2.4% vs 1.2%; P = .004). Although there were no significant differences detected in pulmonary embolisms or above-knee DVTs, the study was not adequately powered to detect differences for these individual outcomes. Further, the 2 groups did not differ in secondary outcomes, including death and major bleeding.