# Perioperative Management and VTE Prophylaxis in Orthopedic Surgery

## Venous Thromboembolism in Orthopedic Surgery

### Epidemiology

Venous thromboembolism (VTE) is the most common preventable cause of death in hospitalized patients. Without prophylaxis, the rates of deep vein thrombosis (DVT) following major orthopedic surgery are strikingly high: 40-60% after total hip arthroplasty, 40-85% after total knee arthroplasty, and 40-60% after hip fracture surgery. Pulmonary embolism carries a 1-2% mortality rate in major orthopedic surgery without prophylaxis. Proximal DVT (above the knee) carries a substantially higher risk of embolization than distal (calf) DVT.

### Virchow's Triad

Three elements conspire to produce venous thrombosis in the surgical patient. Stasis results from immobilization, tourniquet use, and positioning during surgery. Endothelial injury occurs through surgical dissection, retraction, and cement insertion into the medullary canal. Hypercoagulability is driven by the surgical stress response, activation of the inflammatory cascade, and perioperative dehydration.

### Risk Factors

Patient-related risk factors include prior VTE (the strongest individual predictor), active malignancy, inherited thrombophilia, obesity, age over 60, estrogen therapy, smoking, heart failure, and varicose veins. Surgery-related factors include lower extremity procedures, cement use, prolonged operative time, and revision surgery. Immobilization-related factors include prolonged bed rest and long-distance travel.

## Risk Stratification

### Caprini Score

The Caprini score is a validated risk assessment model for surgical patients that assigns points based on individual risk factors. The cumulative score guides the intensity of prophylaxis, with higher scores warranting more aggressive prevention strategies.

### AAOS and ACCP Guidelines

The AAOS guidelines (2011) recommend prophylaxis for all patients undergoing major orthopedic surgery but allow surgeons to choose the specific agent based on each patient's risk profile. The ACCP (Chest) guidelines are more prescriptive, recommending specific agents with LMWH preferred in many scenarios. The discrepancy between these guidelines reflects an ongoing debate in the field about balancing thrombosis prevention against bleeding risk.

## Prophylaxis Options

### Mechanical Prophylaxis

Intermittent pneumatic compression devices (IPCDs) should be applied preoperatively and continued until the patient is fully ambulatory. They can serve as the sole prophylaxis in patients at high bleeding risk since they carry no hemorrhagic complications. Graduated compression stockings (TED hose) are less effective than IPCDs alone and are contraindicated in patients with peripheral arterial disease. Early mobilization is the single most important non-pharmacologic intervention; same-day ambulation after arthroplasty has become the current standard of care.

### Pharmacologic Prophylaxis

| Agent | Route | Dosing | Monitoring | Reversibility | Key Advantage | Key Disadvantage |
|-------|-------|--------|------------|---------------|---------------|-----------------|
| Aspirin | Oral | 81 mg BID | None | N/A | Low cost, oral, PREVENT CLOT evidence | May be less effective in very high-risk patients |
| Enoxaparin (LMWH) | SC | 30 mg BID or 40 mg daily | None routine | Partial (protamine) | Strong evidence base | Injection; HIT risk |
| Rivaroxaban | Oral | 10 mg daily | None | Andexanet alfa | Oral; predictable PK | Cost; wound concerns |
| Apixaban | Oral | 2.5 mg BID | None | Andexanet alfa | Oral; predictable PK | Cost; limited reversibility |
| Warfarin | Oral | Titrate to INR 2.0-2.5 | INR monitoring | Vitamin K / FFP | Long track record; fully reversible | Variable response; drug interactions |
| UFH | SC | 5,000 units BID-TID | None routine | Protamine | Useful in renal insufficiency | Higher HIT risk |
| Fondaparinux | SC | 2.5 mg daily | None | Not reversible | No HIT risk | Long half-life; irreversible |

#### Low-Molecular-Weight Heparin (LMWH)

Enoxaparin, dosed at 30 mg subcutaneously twice daily or 40 mg once daily, is the most extensively studied VTE prophylaxis agent with a strong evidence base. Its advantages include predictable pharmacokinetics and no need for routine monitoring. Disadvantages include the requirement for subcutaneous injection, cost, and a rare risk of heparin-induced thrombocytopenia (HIT). Initiation is typically 12-24 hours postoperatively, balancing the competing risks of thrombosis prevention and surgical site bleeding.

#### Aspirin (ASA)

Aspirin at 81 mg or 325 mg daily has emerged as a viable first-line option following the PREVENT CLOT trial (2023), which demonstrated non-inferiority to LMWH for VTE prevention after fracture surgery. Its advantages are compelling: oral administration, low cost, good tolerability, no injections, and no monitoring requirements. GI side effects are the main disadvantage, and it may be less effective in very high-risk patients. Many centers have now adopted aspirin as first-line prophylaxis for orthopedic trauma patients.

#### Direct Oral Anticoagulants (DOACs)

Rivaroxaban (10 mg daily, starting 6-10 hours postoperatively) and apixaban (2.5 mg twice daily, starting 12-24 hours postoperatively) are FDA-approved for VTE prophylaxis after THA and TKA. Their advantages include oral dosing, no monitoring requirement, and predictable pharmacokinetics. Disadvantages include cost, limited reversibility (andexanet alfa for factor Xa inhibitors), and concern about wound complications in some studies.

#### Warfarin

Warfarin targets an INR of 2.0-2.5 and was historically widely used but is declining due to the need for INR monitoring, highly variable patient response, and numerous drug and food interactions. Its long track record and reversibility with vitamin K or fresh frozen plasma remain advantages in select patients.

#### Unfractionated Heparin (UFH)

UFH at 5,000 units subcutaneously two or three times daily is reversible with protamine and remains useful when renal insufficiency precludes LMWH or DOACs. It carries a higher HIT risk than LMWH.

#### Fondaparinux

Fondaparinux is a synthetic factor Xa inhibitor administered subcutaneously. It carries no HIT risk because it does not interact with platelet factor 4. However, its initiation must be delayed 6-8 hours postoperatively due to bleeding concerns, and its long half-life means it is not reversible.

### Duration of Prophylaxis

For major joint arthroplasty, prophylaxis should continue for a minimum of 10-14 days and be extended to 35 days for high-risk patients. Hip fracture surgery warrants up to 35 days of prophylaxis. For other trauma, duration is based on mobility status and individual risk assessment. Extended prophylaxis beyond hospital discharge is important because most VTE events occur after patients leave the hospital.

## PREVENT CLOT Trial (2023)

### Study Design

This multicenter randomized controlled trial enrolled 12,211 patients with operatively treated extremity fractures and compared aspirin 81 mg twice daily to enoxaparin 30 mg twice daily for VTE prevention. The primary outcome was all-cause mortality at 90 days.

### Key Findings

Aspirin was non-inferior to LMWH for all-cause mortality. There was no significant difference in VTE rates, PE rates, or bleeding complications between groups. The aspirin group reported better patient satisfaction due to oral rather than injectable administration. This landmark trial has substantially shifted practice patterns toward aspirin use in fracture patients.

### Implications

The trial supports aspirin as a reasonable first-line agent for many orthopedic trauma patients, reducing the burden of injections, nursing time, and cost. However, its results do not apply to arthroplasty patients (a different study population), patients with prior VTE, those with known thrombophilia, or patients with active malignancy, all of whom likely require more aggressive prophylaxis.

## Timing Considerations with Neuraxial Anesthesia

### ASRA Guidelines

The American Society of Regional Anesthesia provides specific timing guidelines for anticoagulants around neuraxial procedures. LMWH should be held 12 hours before and 4 hours after the procedure. Rivaroxaban requires a 72-hour hold. Apixaban needs 24-30 hours. Warfarin requires an INR below 1.4 before catheter placement or removal. Aspirin is generally safe for neuraxial procedures with no hold required. The same timing considerations apply to epidural catheter removal.

## Perioperative Medical Optimization

### Preoperative Assessment

Comprehensive preoperative assessment includes cardiac risk stratification using the Revised Cardiac Risk Index (RCRI/Lee criteria) and functional capacity assessment. Pulmonary evaluation should address smoking cessation (ideally 4-8 weeks preoperatively) and screen for sleep apnea. Metabolic optimization targets include HbA1c below 8% with perioperative glucose control for diabetic patients. Nutritional status is assessed through albumin (target above 3.5 g/dL), total lymphocyte count, and prealbumin. Anemia should be corrected preoperatively when possible through iron supplementation or erythropoietin in select cases. Medication management includes anticoagulant and antiplatelet bridging decisions and holding metformin on the day of surgery.

### Blood Management

Tranexamic acid (TXA) has become standard of care for THA and TKA, reducing blood loss and transfusion rates by 30-50%. It can be administered intravenously (1-2 g) or applied topically into the wound (1-3 g). Multiple randomized trials have confirmed its safety with no increased VTE risk. A restrictive transfusion threshold of hemoglobin below 7-8 g/dL is supported by the FOCUS trial. Cell salvage is employed for revision arthroplasty and other major procedures with anticipated high blood loss.

### Infection Prevention

Preoperative MSSA and MRSA screening with decolonization (mupirocin nasal ointment plus chlorhexidine body washes) reduces surgical site infection rates. Intravenous cefazolin should be administered within 60 minutes of incision (vancomycin is substituted for MRSA-positive patients or those with beta-lactam allergy). Antibiotics should be redosed for prolonged cases exceeding 2-3 hours for cefazolin. Chlorhexidine-alcohol skin preparation is preferred over povidone-iodine based on evidence of lower infection rates. Notably, laminar airflow has not been proven to reduce infection rates in arthroplasty despite its widespread adoption.

<image>A comprehensive infographic comparing VTE prophylaxis agents for major orthopedic surgery. Display a table with columns for: Agent (aspirin, LMWH, rivaroxaban, apixaban, warfarin), Route, Dosing, Onset, Monitoring needed, Reversibility, Key advantages, and Key disadvantages. Highlight the PREVENT CLOT trial evidence for aspirin. Use color coding to distinguish injectable from oral agents.</image>

<image>A medical illustration showing Virchow's triad applied to orthopedic surgery. Three overlapping circles labeled Stasis (show a patient immobilized in bed with tourniquet on extremity), Endothelial Injury (show surgical dissection and cement insertion into a femoral canal), and Hypercoagulability (show the inflammatory cascade and platelet activation). At the intersection, show a DVT forming in a deep vein of the lower extremity with red thrombus adhering to the vessel wall.</image>

## Clinical Pearls

The PREVENT CLOT trial has been practice-changing, establishing aspirin as a reasonable first-line VTE prophylaxis agent for most fracture surgery patients. Mechanical prophylaxis with IPCDs should be applied to all patients regardless of chemoprophylaxis since it carries zero bleeding risk. Early mobilization is the single most important non-pharmacologic intervention, and patients should be ambulating the same day whenever possible. TXA is standard of care for arthroplasty, reducing bleeding without increasing VTE risk. ASRA guidelines must always be checked when timing neuraxial anesthesia around anticoagulant administration. The "one size fits all" approach to VTE prophylaxis is outdated; treatment should be tailored to the patient's specific risk factors, bleeding risk, and procedure type. Extended prophylaxis up to 35 days is recommended after THA and hip fracture surgery because most VTEs occur after hospital discharge. Aspirin is not appropriate for all patients; those with prior VTE, active malignancy, or known thrombophilia likely require more aggressive prophylaxis with LMWH or DOACs.

## References

- Major Extremity Trauma Research Consortium (METRC). Aspirin or low-molecular-weight heparin for thromboprophylaxis after a fracture (PREVENT CLOT). *N Engl J Med*. 2023;388(3):203-213.
- Falck-Ytter Y, et al. Prevention of VTE in orthopedic surgery patients: ACCP Evidence-Based Clinical Practice Guidelines (9th Edition). *Chest*. 2012;141(2 Suppl):e278S-e325S.
- AAOS Clinical Practice Guideline: Preventing Venous Thromboembolic Disease in Patients Undergoing Elective Hip and Knee Arthroplasty. 2011.
- Carson JL, et al. Liberal or restrictive transfusion in high-risk patients after hip surgery (FOCUS). *N Engl J Med*. 2011;365(26):2453-2462.
- Horlocker TT, et al. Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: ASRA Evidence-Based Guidelines. *Reg Anesth Pain Med*. 2018;43(3):263-309.