Association of Aspirin with Prevention of Venous Thromboembolism in Patients after Total Knee Arthroplasty Compared with Other Anticoagulants: A Noninferiority Analysis

Abstract

Importance: There has been significant debate in the surgical and medical communities regarding the appropriateness of using aspirin alone for venous thromboembolism (VTE) prophylaxis following total knee arthroplasty (TKA). Objective: To determine the acceptability of aspirin alone vs anticoagulant prophylaxis for reducing the risk of postoperative VTE in patients undergoing TKA. Design, Setting, and Participants: Noninferiority study of a retrospective cohort of TKA cases submitted to the Michigan Arthroplasty Registry Collaborative Quality Initiative at 29 member hospitals, ranging from small community hospitals to large academic and nonacademic medical centers in Michigan. The study included 41537 patients who underwent primary TKA between April 1, 2013, and October 31, 2015. Clinical events were monitored for 90 days after surgery. Data were analyzed between September and October 2016. Exposures: The method of pharmacologic prophylaxis: neither aspirin nor anticoagulants for 668 patients (1.6%), aspirin only for 12831 patients (30.9%), anticoagulant only (eg, low-molecular-weight heparin, warfarin, and Xa inhibitors) for 22620 patients (54.5%), and both aspirin/anticoagulant for 5418 patients (13.0%). Most patients were also using intermittent pneumatic compression stockings. Main Outcome and Measures: The primary composite outcome was the first occurrence of VTE or death. The noninferiority margin was specified as 0.3. The secondary outcome was bleeding events. Results: Of the 41537 patients, 14966 were men (36%), and the mean age was 65.8 years. A VTE event occurred in 573 of 41537 patients (1.38%); 32 of 668 (4.79%) who received no pharmacologic prophylaxis, 149 of 12831 (1.16%) treated with aspirin alone, 321 of 22620 (1.42%) with anticoagulation alone, and 71 of 5418 (1.31%) prescribed both aspirin and anticoagulation. Aspirin only was noninferior for the composite VTE outcome compared with those receiving other chemoprophylaxis (adjusted odds ratio, 0.85; 95% CI, 0.68-1.07, P for inferiority =.007). Bleeding occurred in 457 of 41537 patients (1.10%), 10 of 668 (1.50%) without prophylaxis, 116 of 12831 (0.90%) in the aspirin group, 258 of 22620 (1.14%) with anticoagulation, and 73 of 5418 (1.35%) of those receiving both. Aspirin alone was also noninferior for bleeding complications (adjusted odds ratio, 0.80; 95% CI, 0.63-1.00, P for inferiority