Aspirin may be effective at preventing venous thromboembolism following total knee (TKA) or total hip arthroplasty (THA). Current evidence is limited by bias as many surgeons who use aspirin prescribe for high-risk patients alternative chemoprophylactic agents. Therefore, this study aimed to evaluate the risk of pulmonary embolism (PE) and deep vein thrombosis (DVT) in patients who received aspirin and warfarin while accounting for surgeon selection bias.
A national database was queried for patients undergoing primary elective TKA or THA from 2015 to 2020. Patients whose surgeon used aspirin in >90% of their patients were compared to patients whose surgeon utilized warfarin in >90% of cases. Instrumental variable analyses (IVA) were performed to assess for PE, DVT, and transfusion while accounting for selection bias. Among TKA patients, 26,657 (18.8%) were in the warfarin cohort and 115,005 (81.2%) were in the aspirin cohort. Among THA patients, 13,035 (17.7%) were in the warfarin cohort and 60,726 (82.3%) were in the aspirin cohort.
Analyses were unable to identify a difference in the risk of PE (TKA: adjusted odds ratio [aOR]: 0.98, p=0.659; THA: aOR=0.93, p=0.310) and DVT (TKA: aOR=1.05, p=0.188; THA: aOR=0.96, p=0.493) between the aspirin and warfarin cohorts. However, the aspirin cohort was associated with a lower risk of transfusion (TKA: aOR=0.58, p<0.001, THA: 0.84, p<0.001).
After accounting for surgeon selection bias, aspirin was as effective as warfarin at preventing PE and DVT following TKA and THA. Furthermore, aspirin was associated with a lower risk of transfusion compared to warfarin.

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