Aspirin alone matched rivaroxaban-then-aspirin for preventing clots after hip and knee replacement, Canadian NEJM trial finds

A large Canadian clinical trial published in the New England Journal of Medicine suggests that plain aspirin may be enough for many patients to prevent dangerous blood clots after total hip or knee replacement. The study was led by Dr Sudeep Shivakumar, head of haematology at Dalhousie University, and administered by Nova Scotia Health.

The trial

• Randomised and double-blind: neither patients nor investigators knew which treatment each person received.
• About 5,300 patients at 15 university-affiliated centres across Canada.
• It compared aspirin alone with a common strategy of rivaroxaban (a blood thinner) for five days, followed by aspirin.
• Result, as summarised by the university: aspirin alone was as safe and as effective as the rivaroxaban-then-aspirin approach.
• Funding came entirely from the Canadian Institutes of Health Research; the team stresses there was no pharmaceutical or private funding. Planning began in 2018, and the trial was completed in early 2026.

Why it matters

Joint replacements are among the most common operations worldwide, and clot prevention must be balanced against bleeding risk. A one-drug approach could make recovery simpler; Shivakumar said it gives patients options “so they can make decisions with their healthcare provider”. The study did not include a formal cost analysis, although aspirin is cheap and widely available.

Limitations

This summary is based on the university’s news release, which does not give the clot and bleeding rates for each group; readers should consult the NEJM paper for the exact results and non-inferiority margins. The trial covered elective hip and knee replacements in Canada and may not apply to other operations or to patients with other clotting risks. Do not change any prescribed medication without talking to your doctor or surgeon.