- Design
- Systematic review and meta-analysis of 16 randomised trials
- Population
- 21,265 patients after total hip or knee arthroplasty
- Primary outcome
- Any DVT, symptomatic DVT and symptomatic VTE
- Effect
- Symptomatic VTE RR 1.70 (95% CI 1.33–2.18), aspirin vs anticoagulant; not significant without CRISTAL
An updated systematic review and meta-analysis pooled 16 randomised trials with 21,265 patients comparing aspirin-based thromboprophylaxis with anticoagulant regimens after total hip or knee arthroplasty, searching to July 2026.
In the main analysis, aspirin was associated with more symptomatic DVT (RR 1.79, 95% CI 1.35–2.38), symptomatic VTE (RR 1.70, 1.33–2.18) and pulmonary embolism (RR 1.89, 1.33–2.68). It was associated with less minor bleeding (RR 0.47) and bruising, with no significant difference in major or clinically relevant bleeding.
The result leans heavily on CRISTAL, the large cluster-randomised registry trial. With CRISTAL removed, or with only low-risk-of-bias trials, the symptomatic DVT and VTE differences were no longer significant, and analyses using CRISTAL's cluster-adjusted estimates found no significant differences in the primary outcomes. So this does not overturn guidelines that allow aspirin. What it does support is reserving aspirin for patients at lower clot risk and preferring an anticoagulant in those at higher risk, where the trade-off in bleeding is worth more.
- Consider an anticoagulant rather than aspirin for patients with higher VTE risk after hip or knee replacement.
- Aspirin remains a guideline-supported option for lower-risk patients; this analysis does not change that.
- Expect less minor bleeding and bruising with aspirin, but no clear reduction in major bleeding.
- Check your local protocol is risk-stratified rather than a single default agent.
Why it matters
Aspirin has become the default in many units; this asks whether it should be the default for everyone.
Don't overread it
The symptomatic VTE signal depended on one cluster trial and has not changed any guideline.
The statistics, in plain English
A risk ratio of 1.70 means symptomatic clots were about 70% more common with aspirin in the pooled trials. Because the finding disappeared when one large trial was removed, it is fragile: the true difference could be much smaller.
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