Research Summary
Aspirin vs. Blood Thinners After Knee or Hip Replacement: Review of 16 Trials Finds More Clots but Less Bruising With Aspirin
After a knee or hip replacement, aspirin was linked to more symptomatic blood clots than prescription anticoagulant drugs, but to less minor bleeding and bruising. The systematic review and meta-analysis was published in Medicina.
What was studied
Joint replacement raises the risk of venous thromboembolism (VTE), meaning blood clots in the leg veins (deep vein thrombosis, or DVT) that can travel to the lungs (pulmonary embolism, or PE). Aspirin is widely used to prevent these clots, but doctors still debate whether it works as well as anticoagulant blood thinners.
The researchers searched four major databases through July 2026 and pooled 16 randomized controlled trials involving 21,265 people who had total knee or hip replacement. Each trial compared an aspirin-based plan with an anticoagulant regimen.
Key findings
- Aspirin was linked to a higher risk of symptomatic DVT (about 1.8 times), symptomatic VTE (about 1.7 times) and pulmonary embolism (about 1.9 times).
- Aspirin was linked to roughly half the risk of minor bleeding and less bruising.
- There was no significant difference in major or clinically relevant bleeding, wound problems, transfusions or deaths.
- When one large trial (CRISTAL) was removed, or only trials at low risk of bias were analyzed, the higher symptomatic clot risk was no longer statistically significant, although any DVT was higher with aspirin in the low-risk trials.
What it means for people with knee pain
If you are planning a knee replacement, the choice of clot prevention involves a trade-off: aspirin may mean fewer minor bleeds and bruises, while anticoagulants may prevent somewhat more clots. Your personal clot and bleeding risk matters, so discuss the plan with your surgeon and do not change prescribed medication on your own.
Limitations
The authors urge caution. The results leaned heavily on one large trial, changed depending on which trials and methods were used, and the studies differed in drug choices and how outcomes were defined. Hip and knee patients were analyzed together.
Frequently asked questions
- Is aspirin enough to prevent blood clots after knee replacement?
- In this review of 16 trials, aspirin was linked to more symptomatic clots than anticoagulant drugs, but that difference faded when one large trial was excluded. Your surgeon will weigh your own risk.
- Does aspirin cause less bleeding than blood thinners after surgery?
- It was linked to less minor bleeding and bruising, but there was no significant difference in major or clinically relevant bleeding.
- Should I switch my clot prevention medicine after reading this?
- No. Do not change prescribed medication on your own. Talk with your surgeon about the trade-offs for your situation.
Sudden severe pain, swelling, or can't bear weight? Seek medical care promptly. In an emergency call 911.