In a patient undergoing elective hip arthroplasty with low to moderate bleeding risk and no contraindications (no active gastrointestinal ulcer, recent major bleeding, aspirin allergy, severe renal impairment, or need for full anticoagulation), is low‑dose aspirin 81 mg twice daily for 4 weeks appropriate for postoperative venous thrombo‑embolism prophylaxis, or should low‑molecular‑weight heparin or a direct oral anticoagulant be used?

Aspirin for VTE Prophylaxis After Hip Arthroplasty

Low-dose aspirin 81 mg twice daily for 4 weeks is appropriate and effective for VTE prophylaxis in low-to-moderate risk patients undergoing elective hip arthroplasty, with lower bleeding risk than higher doses and comparable efficacy to LMWH or DOACs. 1, 2, 3

Recommended Aspirin Regimen

The optimal regimen is aspirin 81 mg twice daily (BID) for 35 days (approximately 4-5 weeks) starting the day of surgery. 1, 2

• The American College of Chest Physicians recommends 35 days of aspirin based on the landmark PEP trial of 17,444 patients, which demonstrated VTE risk reduction (RR 0.71; 95% CI: 0.54-0.94) with only modest bleeding increase (2.9% vs 2.4%; P = 0.04). 1
• Low-dose aspirin 81 mg BID is superior to 325 mg once or twice daily, with significantly lower bleeding rates (2.5% vs 7.6%, p = 0.0029) and comparable VTE prevention (1.5% vs 2.7%, p = 0.41). 2
• A large retrospective study of 3,936 THA patients confirmed no difference in symptomatic VTE between 81 mg BID (0.6%) and 325 mg BID (1.0%), but bleeding was significantly reduced with the lower dose. 3

Comparison to LMWH and DOACs

Aspirin monotherapy is appropriate as first-line prophylaxis in low-to-moderate risk patients, with LMWH or DOACs reserved for higher-risk scenarios. 1, 4, 5

• Extended LMWH prophylaxis is more effective than aspirin but generates costs of EUR 10,000-20,000 per PE prevented when extended to 6 weeks, while aspirin remains cost-saving in all scenarios. 6
• A risk-stratified approach using aspirin for low-risk patients (94-97% of elective THA patients) showed no increase in VTE events compared to warfarin, with significantly fewer bleeding events (HR = 0.19, p = 0.048). 4
• Staged prophylaxis using LMWH in-hospital followed by aspirin after discharge demonstrated excellent safety in 9,035 patients with fatal PE rate of 0.03% and all-cause mortality of 0.07%. 5

Critical Timing Considerations

Start aspirin on the day of surgery and continue for 35 days; if aspirin was held preoperatively, resume within 24 hours postoperatively once hemostasis is achieved. 1

• For patients already on aspirin for cardiovascular indications, the American College of Chest Physicians recommends continuing it throughout the perioperative period without interruption. 1
• If aspirin must be held preoperatively (which is rarely necessary for hip arthroplasty), discontinue 5-7 days before surgery, not the outdated 10-day window. 1
• Maximal antiplatelet effect occurs within minutes of aspirin administration, providing immediate VTE and cardiovascular protection upon resumption. 1

Evidence Quality and Guideline Conflicts

The American College of Chest Physicians guidelines are methodologically superior to the American Association of Orthopedic Surgeons (AAOS) recommendations, which lack evidence-based support for many of their aspirin dosing recommendations. 7

• The AAOS recommended aspirin 325 mg twice daily for 6 weeks, but this recommendation has no supporting evidence—the PEP study evaluated 162 mg/day, and there is no evidence that 650 mg/day is more effective or that 6 weeks is necessary. 7
• The AAOS guidelines were criticized for selective literature review, disregarding randomized trials showing statistically significant PE reductions with aspirin, and making recommendations not linked to their own analysis. 7
• The American College of Chest Physicians methodology is explicit and rigorous, considering only high-quality randomized trial evidence and basing recommendations on patient-important outcomes. 7

Common Pitfalls to Avoid

• Do not use aspirin 325 mg twice daily (650 mg/day total)—this outdated AAOS recommendation increases bleeding without additional VTE protection. 7, 2
• Do not hold aspirin for 10 days preoperatively—this unnecessarily increases thrombotic risk; 5-7 days is sufficient if holding is required. 1
• Do not assume all patients need aspirin held—hip arthroplasty is not a closed-space surgery where minor bleeding causes catastrophic complications. 1
• Do not use LMWH or heparin for "bridging" when holding aspirin—this increases bleeding risk without proven benefit. 1
• Do not forget medication reconciliation for over-the-counter NSAIDs that compound antiplatelet effects. 1

Special Populations

For patients on dual antiplatelet therapy (DAPT), continue aspirin throughout but hold the P2Y12 inhibitor (clopidogrel 5 days, ticagrelor 3-5 days, prasugrel 7 days before surgery). 1, 7

• Patients with coronary stents or high cardiovascular risk should have aspirin restarted as soon as possible postoperatively, ideally within 24 hours. 1
• For patients taking aspirin for secondary cardiovascular prevention (prior MI, stroke, coronary stents), continue it indefinitely throughout the perioperative period—do not stop at 35 days. 1