What venous thromboembolism prophylaxis should be started for a patient with a hip fracture who has not yet undergone surgery?

VTE Prophylaxis for Hip Fracture Patients Awaiting Surgery

For hip fracture patients who have not yet undergone surgery, initiate pharmacologic VTE prophylaxis with LMWH (such as enoxaparin 40 mg subcutaneously once daily) or fondaparinux 2.5 mg subcutaneously once daily as soon as possible after admission, combined with mechanical prophylaxis (intermittent pneumatic compression devices or graduated compression stockings). 1, 2, 3

Rationale and Evidence Base

Hip fracture patients represent one of the highest-risk surgical populations for VTE, with studies showing DVT prevalence of 37% and pulmonary embolism rates of 6% when screened systematically 2. Recent evidence demonstrates that VTE may be present within 24 hours of injury in a substantial proportion of patients, with 12.6% of hip fracture patients having VTE on immediate screening 4.

Pharmacologic Options

The evidence supports several pharmacologic agents for preoperative prophylaxis:

• LMWH (preferred): Enoxaparin 40 mg once daily or dalteparin 5000 IU once daily 5, 1
• Fondaparinux: 2.5 mg once daily (dose-adjust to 1.5 mg if CrCl 30-50 mL/min) 5, 6
• Low-dose UFH: 5000 U twice or three times daily 5, 6

The timing of initiation matters critically. Guidelines recommend starting prophylaxis before surgery when surgery is delayed 1. A large Norwegian registry study of 45,913 hip fractures found that preoperative versus postoperative LMWH initiation showed similar mortality (RR 1.01) and reoperation rates (RR 0.99), but postoperative initiation reduced intraoperative bleeding complications (RR 0.67) 7. However, this must be balanced against the reality that many patients experience surgical delays, during which they remain at high VTE risk without protection.

Mechanical Prophylaxis

Combine pharmacologic prophylaxis with mechanical methods (intermittent pneumatic compression devices or graduated compression stockings) 2, 3. These should be applied immediately and continued intraoperatively. Mechanical devices alone are insufficient as sole prophylaxis due to poor compliance and suboptimal efficacy 8.

Critical Clinical Considerations

High-Risk Scenarios Requiring Immediate Action

For patients presenting ≥7 days after fracture, the risk of pre-existing asymptomatic DVT is extremely high 9. Consider:

• Immediate D-dimer testing (if elevated, proceed to imaging)
• CT angiography or duplex ultrasound screening for VTE
• If DVT is confirmed preoperatively, consider IVC filter placement before surgery to prevent fatal intraoperative PE 9

Recent data shows 68.2% of VTE in hip fracture patients is diagnosed within 24 hours of injury, with one-third having pulmonary embolism 4. Risk factors for preoperative VTE include: overweight status (OR 2.12), femur shaft fractures (OR 4.83), and notably, patients NOT on prior anticoagulants (OR 0.36 for those on anticoagulants) 4.

Contraindications and Special Populations

If pharmacologic prophylaxis is contraindicated due to active bleeding or high bleeding risk, use mechanical prophylaxis alone until bleeding risk diminishes, then add pharmacologic agents 5.

For patients already on anticoagulation (for atrial fibrillation, prior VTE, etc.), continue their therapeutic anticoagulation through the preoperative period when possible. The 2021 Association of Anaesthetists guidelines provide comprehensive management algorithms for patients on DOACs, warfarin, and antiplatelet agents, emphasizing that delaying surgery >36 hours for anticoagulation reversal significantly increases mortality risk 10.

Aspirin Alone is Inadequate

Do not use aspirin as sole prophylaxis (Grade 1A recommendation) 6. While aspirin reduces VTE risk compared to placebo, it provides suboptimal protection compared to anticoagulants and does not meet the standard of care for this highest-risk population 8, 11.

Duration and Continuation

Prophylaxis should continue throughout the preoperative waiting period and be maintained postoperatively for a minimum of 10-14 days, with consideration for extended prophylaxis up to 35 days 5, 1, 6. The 2022 AAOS guidelines strongly recommend VTE prophylaxis for hip fracture patients, with continuation for at least 4 weeks postoperatively 12.

Common Pitfalls to Avoid

1. Delaying prophylaxis initiation while awaiting surgery—start immediately upon admission
2. Using aspirin alone—this is explicitly not recommended
3. Omitting mechanical prophylaxis—always combine with pharmacologic agents
4. Failing to screen high-risk patients (delayed presentation >7 days, elevated D-dimer)
5. Unnecessarily delaying surgery for anticoagulation reversal when risks outweigh benefits
6. Forgetting renal dose adjustments for fondaparinux and LMWH in patients with renal impairment