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Original Investigation
October 17, 2018

Association of Aspirin With Prevention of Venous Thromboembolism in Patients After Total Knee Arthroplasty Compared With Other AnticoagulantsA Noninferiority Analysis

Author Affiliations
  • 1Department of Orthopaedic Surgery, University of Michigan, Ann Arbor
  • 2Quality Institute, St Joseph Mercy Health System, Ann Arbor, Michigan
JAMA Surg. Published online October 17, 2018. doi:10.1001/jamasurg.2018.3858
Key Points

Question  Is aspirin alone inferior to other anticoagulant medications for reducing the risk of venous thromboembolism (VTE) in patients after total knee arthroplasty?

Findings  In this cohort study, 573 of 41 537 patients after total knee arthroplasty sustained a VTE event. Of those receiving prophylaxis, 541 had a VTE event; 149 if receiving aspirin alone, 321 when prescribed anticoagulation alone, and 71 if prescribed both aspirin and anticoagulation.

Meaning  Aspirin alone may be an appropriate alternative to other pharmacologic prophylaxis in preventing VTE for patients undergoing total knee arthroplasty.


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 41 537 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 12 831 patients (30.9%), anticoagulant only (eg, low-molecular-weight heparin, warfarin, and Xa inhibitors) for 22 620 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 41 537 patients, 14 966 were men (36%), and the mean age was 65.8 years. A VTE event occurred in 573 of 41 537 patients (1.38%); 32 of 668 (4.79%) who received no pharmacologic prophylaxis, 149 of 12 831 (1.16%) treated with aspirin alone, 321 of 22 620 (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 41 537 patients (1.10%), 10 of 668 (1.50%) without prophylaxis, 116 of 12 831 (0.90%) in the aspirin group, 258 of 22 620 (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 <.001).

Conclusions and Relevance  In this study of patients undergoing TKA, aspirin was not inferior to other anticoagulants in the postoperative rate of VTE or death. Aspirin alone may provide similar protection from postoperative VTE compared with other anticoagulation treatments.

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