Can a Two-Drug combo beat aspirin alone for preventing clots after joint surgery?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Patients undergoing elective THA/TKA at the participating institutions will be potentially eligible for this study 2. Written informed consent in accordance with federal, local and institutional guidelines Exclusion Criteria: 1. Previous documented VTE (proximal DVT or any PE) 2. Hip or lower limb fracture in the previous three months, not related to present surgery 3. Metastatic cancer 4. Life expectancy less than 6 months 5. History of major bleeding that in the judgment of the investigator precludes use of anticoagulant prophylaxis 6. History of aspirin allergy, active peptic ulcer disease or gastritis that in the judgment of investigator precludes use of aspirin 7. History of significant hepatic disease or any other condition that in the judgment of the investigator precludes the use of rivaroxaban 8. Creatinine clearance less than 15 ml per minute 9. Pre-operative platelet count less than 100 x 109 /L 10. Need for long-term anticoagulation due to a pre-existing co-morbid condition or due to the development of VTE following surgery but prior to randomization 11. Received anticoagulation post operatively 12. Bilateral THA/TKA or simultaneous hip and knee arthroplasty 13. Major surgical procedure within the previous 3 months 14. Requirement for major surgery post arthroplasty within a 90 day period 15. Chronic daily aspirin use with dose greater than 100 mg a day 16. Women of childbearing potential who are not abstinent or do not use effective contraception or are breast-feeding throughout the study drug period 17. Unwilling or unable to give consent 18. Previous participation in the EPCAT III study 19. Under 18 years of age 20. Concomitant use of drugs that are strong inhibitors of P-gp AND CYP3A4 (e.g., systemic treatment with ketoconazole, itraconazole, or ritonavir) or strong inducers of P-gp AND CYP3A4 (e.g., rifampicin, phenytoin, carbamazepine, phenobarbital, St. John's Wort) 21. Known allergy to food dye