VENOUS THROMBOEMBOLISM - COMPREHENSIVE
Virchow's Triad | Risk Stratification | Prophylaxis Protocols | Prevention & Treatment
VIRCHOW'S TRIAD
Critical Must-Knows
- Virchow's triad is the pathophysiological foundation: Stasis + Hypercoagulability + Endothelial injury
- Risk stratification is mandatory: Use Caprini score or NICE guidelines to determine prophylaxis intensity
- Extended prophylaxis for 35 days is standard after THA, TKA, and hip fracture surgery (ACCP Grade 1B)
- LMWH and DOACs are superior to aspirin alone for VTE prevention but aspirin is acceptable for lower-risk patients
- DVT diagnosis: Compression ultrasound (sensitivity over 95% for proximal DVT)
- PE diagnosis: CTPA is gold standard; V/Q scan if contrast contraindicated
Examiner's Pearls
- "Virchow's triad explains why ALL orthopaedic surgery patients are at VTE risk
- "Caprini score 5 or higher = high risk requiring chemical prophylaxis
- "LMWH started 12h preop (European) or 12-24h postop (North American) - know both protocols
- "DOACs (rivaroxaban, apixaban) are non-inferior to LMWH with better compliance
- "Post-thrombotic syndrome affects 20-50% of DVT patients - compression reduces risk
Critical VTE Exam Concepts - High-Yield Alert
Virchow's Triad is Non-Negotiable
You MUST know the triad. Stasis (immobility), Hypercoagulability (trauma response, inherited disorders), Endothelial injury (surgery, fractures). Examiners expect you to explain how each component contributes to VTE risk in orthopaedic patients and how your prophylaxis strategy addresses each element.
Risk Stratification Determines Management
Know Caprini Score cutoffs: Score 0-1 = low risk (early ambulation), 2 = moderate (mechanical), 3-4 = high (mechanical + chemical), 5 or higher = highest (extended prophylaxis 35 days). NICE guidelines are alternative. Must individualize based on bleeding risk.
Timing of Chemical Prophylaxis
Critical timing knowledge: LMWH 12h before surgery (European) OR 12-24h after surgery (North American). DOACs started 6-12h postop (rivaroxaban 6-10h, apixaban 12-24h). Never give before spinal/epidural - risk of epidural hematoma. Know contraindications.
Extended Prophylaxis Duration
35 days is the standard for THA, TKA, hip fracture (ACCP Grade 1B). VTE risk persists 6-12 weeks postop. Stopping at hospital discharge is suboptimal. Aspirin alone may be used for extended phase if LMWH used perioperatively (AAOS).
VTE Prophylaxis Agents - Comparative Overview
| Agent | Mechanism | Dosing | Advantages | Disadvantages |
|---|---|---|---|---|
| Enoxaparin (LMWH) | Anti-Xa and anti-IIa inhibition | 40mg SC daily or 30mg BD | Gold standard, reversible with protamine, renal dosing available | Injection required, HIT risk (0.5%), monitoring if renal impairment |
| Rivaroxaban (DOAC) | Direct Factor Xa inhibitor | 10mg PO daily | Oral, fixed dose, no monitoring, non-inferior to LMWH | No reversal agent (andexanet expensive), avoid CrCl less than 15 |
| Apixaban (DOAC) | Direct Factor Xa inhibitor | 2.5mg PO BD | Oral, renal-safe (less than 25% renal), low bleeding | Twice daily dosing, no reversal widely available |
| Aspirin | COX-1 inhibition (antiplatelet) | 100-300mg PO daily | Cheap, oral, low bleeding, patient familiarity | Inferior efficacy vs LMWH/DOAC, consider only for lower-risk or extended phase |
| Warfarin | Vitamin K antagonist | Target INR 2-3 | Oral, reversible with vitamin K/FFP, cheap | Requires INR monitoring, interactions, slow onset, bridging needed |
| UFH | Anti-IIa greater than anti-Xa | 5000 units SC BD-TDS | Fully reversible, short half-life, safe in renal failure | Highest HIT risk (2-3%), requires more frequent dosing |
SHEVirchow's Triad
Memory Hook:SHE is at risk for VTE - Stasis, Hypercoagulability, Endothelial injury. All three present in major orthopaedic surgery!
HIPSCaprini Risk Factors (5-point items)
Memory Hook:HIPS fractures and these factors score 5 points each on Caprini - automatic high-risk status!
CLOTDVT Clinical Features
Memory Hook:Look for a CLOT - Calf pain, Leg swelling, Observable veins, Temperature change. But remember: 50% of DVTs are asymptomatic!
Overview and Epidemiology
Venous thromboembolism (VTE), encompassing deep vein thrombosis (DVT) and pulmonary embolism (PE), represents one of the most significant preventable complications in orthopaedic surgery. Understanding VTE pathophysiology, risk stratification, and evidence-based prophylaxis is mandatory knowledge for fellowship examinations.
Definition:
- DVT: Thrombus formation in the deep venous system, most commonly in lower extremity (iliac, femoral, popliteal, calf veins)
- PE: Embolization of thrombus to pulmonary arterial circulation, causing ventilation-perfusion mismatch
- VTE: Umbrella term encompassing the spectrum from asymptomatic calf DVT to fatal massive PE
Epidemiology in Orthopaedic Surgery:
VTE Incidence Without Prophylaxis
| Procedure | DVT Rate | Proximal DVT | Fatal PE |
|---|---|---|---|
| Total hip arthroplasty | 40-60% | 15-25% | 0.5-2% |
| Total knee arthroplasty | 40-84% | 10-20% | 0.5-1.5% |
| Hip fracture surgery | 40-60% | 15-30% | 2-7% |
| Knee arthroscopy | 5-15% | 1-2% | Less than 0.1% |
| Spine surgery | 15-40% | 5-10% | 0.3-0.5% |
| Lower limb trauma | 40-80% | 10-20% | 1-2% |
With Prophylaxis:
- DVT rates reduced to 10-20% (mechanical only) or 1-5% (mechanical + chemical)
- Fatal PE reduced to less than 0.5% with adequate prophylaxis
- NNT (number needed to treat) approximately 7 to prevent one symptomatic VTE
Australian Context
VTE remains a leading cause of preventable hospital death in Australia. The Australian Commission on Safety and Quality in Health Care mandates VTE risk assessment for all hospital admissions. Compliance with prophylaxis protocols is a key hospital performance indicator.
Pathophysiology - Virchow's Triad
Rudolf Virchow described his famous triad in 1856, identifying three factors that predispose to venous thrombosis. All three are present in major orthopaedic surgery, explaining the extremely high VTE risk in this population.
Venous Stasis
Mechanism:
- Normal venous return depends on calf muscle pump action and competent venous valves
- Immobility eliminates calf muscle pump function
- Venous pooling allows activated clotting factors to accumulate locally
- Reduced clearance of activated factors overwhelms natural anticoagulant systems
Orthopaedic Causes:
- Preoperative immobility (hip fracture, multiple trauma)
- Intraoperative positioning (hip flexion, rotation)
- Postoperative bed rest and reduced mobility
- Cast immobilization
- Lower limb paralysis (stroke, spinal cord injury)
- Tourniquet application (distal stasis during inflation)
Prevention Strategies:
- Early mobilization (day 0-1 post-surgery when safe)
- Mechanical prophylaxis (IPC devices, GCS)
- Ankle exercises and calf pump activation
- Avoiding prolonged hip flexion
- Physiotherapy protocols
Calf Muscle Pump
The calf muscle pump generates pressures of 200-300 mmHg during contraction, propelling blood centrally through competent valves. Loss of this pump (immobility) reduces venous velocity by 50% and allows thrombus formation in valve pockets.
Combined Effect in Orthopaedic Surgery:
All three elements of Virchow's triad are present simultaneously in major orthopaedic procedures, creating a "perfect storm" for VTE:
- Preoperative immobility (stasis)
- Surgical trauma and tissue factor release (hypercoagulability)
- Direct vessel injury and manipulation (endothelial injury)
This explains why THA and TKA have the highest VTE risk of any elective surgical procedures and why prophylaxis is mandatory.
Clinical Presentation
Deep Vein Thrombosis - Clinical Features
Important: Up to 50% of DVTs are asymptomatic, detected only on screening ultrasound. Clinical diagnosis is unreliable (sensitivity 50-60%, specificity 50%).
Symptoms:
- Calf pain (most common) - often described as "cramping" or "tightness"
- Leg swelling - may be acute or insidious onset
- Warmth and redness over affected area
- Heaviness or aching in leg
- Pain worse with standing or walking
Signs:
- Unilateral leg edema (more than 3cm difference significant)
- Pitting edema
- Calf tenderness on palpation
- Increased warmth
- Erythema (may be subtle)
- Superficial venous distension
- Homans' sign (calf pain on forced dorsiflexion) - unreliable, only 50% sensitive
Wells Score for DVT
| Clinical Feature | Points |
|---|---|
| Active cancer (treatment within 6 months or palliative) | +1 |
| Paralysis, paresis, or recent lower limb immobilization | +1 |
| Bedridden more than 3 days or major surgery within 12 weeks | +1 |
| Localized tenderness along deep venous system | +1 |
| Entire leg swollen | +1 |
| Calf swelling more than 3cm compared to other leg | +1 |
| Pitting edema confined to symptomatic leg | +1 |
| Collateral superficial veins (non-varicose) | +1 |
| Previously documented DVT | +1 |
| Alternative diagnosis at least as likely | -2 |
Wells Score Interpretation:
- 0 or less: Low probability (5% DVT prevalence)
- 1-2: Moderate probability (17% DVT prevalence)
- 3 or more: High probability (53% DVT prevalence)
Clinical Tip
In postoperative orthopaedic patients, the Wells score has limited utility because multiple risk factors are already present (recent surgery, immobility). Have a LOW threshold for imaging. If clinical suspicion exists, proceed directly to compression ultrasound regardless of Wells score.
Investigations
DVT Diagnostic Pathway
D-dimer:
- Highly sensitive (95%) but poorly specific (50%)
- Elevated in: surgery, trauma, pregnancy, cancer, infection, inflammation
- Negative D-dimer reliably excludes DVT in LOW pretest probability patients
- In postoperative orthopaedic patients: D-dimer is almost always elevated - DO NOT use to rule out DVT
D-dimer Limitation
D-dimer has NO role in ruling out DVT in postoperative orthopaedic patients. It will be elevated from surgery and does not add diagnostic value. Proceed directly to imaging if DVT is suspected.
Compression Ultrasound (Gold Standard):
- Sensitivity: 95% for proximal DVT, 70-80% for calf DVT
- Specificity: 98%
- Technique: Inability to fully compress vein with probe pressure is diagnostic
- Also visualizes thrombus echogenicity and venous flow patterns
- Advantages: Non-invasive, no radiation, bedside available
When to Image:
- Any clinical suspicion of DVT postoperatively
- Unexplained leg swelling, pain, or warmth
- Before anticoagulation cessation if DVT was diagnosed
- PE diagnosed - evaluate for DVT source
Other Imaging:
- CT venography: For pelvic and IVC extension, if US non-diagnostic
- MR venography: Alternative for pelvic veins, no radiation
- Contrast venography: Historical gold standard, rarely used now (invasive)
DVT Diagnostic Algorithm by Pretest Probability
| Probability | D-dimer | Ultrasound | Interpretation |
|---|---|---|---|
| Low (Wells 0 or less) | If negative: DVT excluded | If D-dimer positive: proceed to US | Serial US if negative but high suspicion |
| Moderate (Wells 1-2) | Not reliable | Proceed directly | Consider repeat US in 5-7 days if negative |
| High (Wells 3+) | Do not use | Proceed directly | Consider venography if negative and high suspicion |
| Postoperative ortho | Do not use | Proceed directly | Low threshold for imaging |
Management
Risk Stratification Systems
Caprini Score: The Caprini Risk Assessment Model is the most widely used tool for VTE risk stratification in surgical patients.
Caprini Score - Key Risk Factors
| 1 Point Each | 2 Points Each | 3 Points Each | 5 Points Each |
|---|---|---|---|
| Age 41-60 | Age 61-74 | Age 75 or more | Hip, pelvis, leg fracture |
| Minor surgery | Arthroscopic surgery | Prior VTE | Stroke (less than 1 month) |
| BMI over 25 | Major surgery over 45 min | Family history VTE | Spinal cord injury |
| Varicose veins | Malignancy | Positive thrombophilia | Elective arthroplasty |
| OCP/HRT | Bed rest over 72h |
Caprini Score Interpretation:
- 0: Very low risk (0.5% VTE) - Early ambulation only
- 1-2: Low risk (1.5% VTE) - Mechanical prophylaxis
- 3-4: Moderate risk (3% VTE) - Mechanical + chemical prophylaxis
- 5 or more: High risk (6% VTE) - Mechanical + chemical + extended prophylaxis (35 days)
NICE Guidelines: UK National Institute for Health and Care Excellence provides alternative risk assessment.
Key Principles:
- ALL orthopaedic inpatients require VTE risk assessment
- ALL patients undergoing THA, TKA, hip fracture surgery are automatically HIGH RISK
- Must also assess bleeding risk to balance prophylaxis
Bleeding Risk Assessment
Prophylaxis must balance VTE risk against bleeding risk. Consider bleeding risk factors: active bleeding, severe thrombocytopenia (platelets less than 50), coagulopathy, high-bleeding-risk surgery (spine, intracranial), recent major bleeding. If bleeding risk is high, use mechanical prophylaxis only until bleeding risk diminishes.
Surgical Management - IVC Filters
Inferior Vena Cava (IVC) Filter Indications
Absolute Indications:
- Acute proximal DVT or PE with absolute contraindication to anticoagulation
- Recurrent PE despite adequate anticoagulation
- Complications of anticoagulation requiring cessation (major bleeding)
Relative Indications (Controversial):
- Prophylactic filter in very high-risk trauma (controversial, not recommended routinely)
- Free-floating iliofemoral thrombus (some advocate, others anticoagulate)
- Massive PE with residual DVT where further embolization would be fatal
- Poor cardiopulmonary reserve where any PE would be catastrophic
NOT Indicated:
- Routine prophylaxis in trauma or orthopaedic surgery
- As alternative to anticoagulation when anticoagulation is feasible
- For calf DVT only
IVC Filters Are Not Routine Prophylaxis
Do NOT place IVC filters for VTE prophylaxis in trauma or orthopaedic patients who can receive anticoagulation. The PREPIC-2 trial showed no benefit of prophylactic filters in addition to anticoagulation, with increased DVT rates in filter group. Filters are for patients who CANNOT be anticoagulated.
Complications
VTE Complications and Management
| Complication | Incidence | Presentation | Management |
|---|---|---|---|
| Post-thrombotic syndrome | 20-50% after proximal DVT | Chronic leg swelling, pain, skin changes, ulceration | Prevention: compression stockings for 2 years. Treatment: compression, elevation, wound care for ulcers |
| Recurrent VTE | 5-10% at 1 year on anticoagulation | New DVT or PE symptoms | Ensure therapeutic anticoagulation, consider extended/indefinite therapy |
| Chronic thromboembolic pulmonary hypertension (CTEPH) | 2-4% after PE | Persistent dyspnea 6+ months post-PE | Referral to pulmonary hypertension centre, pulmonary endarterectomy |
| Phlegmasia cerulea dolens | Rare | Massive iliofemoral DVT, cyanotic limb, compartment syndrome risk | Urgent surgical thrombectomy or catheter-directed thrombolysis, fasciotomy if compartment syndrome |
| Anticoagulation bleeding | 3-5% major bleeding on therapeutic anticoagulation | GI bleed, intracranial hemorrhage, surgical site bleeding | Hold anticoagulation, reversal agents, transfusion, surgical hemostasis if needed |
| Heparin-induced thrombocytopenia (HIT) | 0.5% with LMWH, 2-3% with UFH | Platelet drop more than 50% at 5-14 days, paradoxical thrombosis | Stop all heparin, switch to non-heparin anticoagulant (argatroban, fondaparinux) |
HIT Recognition
Heparin-Induced Thrombocytopenia is a prothrombotic emergency despite low platelets. 4Ts score (Thrombocytopenia, Timing, Thrombosis, oTher causes) helps assess probability. If HIT suspected: (1) Stop ALL heparin immediately, (2) Start alternative anticoagulant (argatroban, fondaparinux - NOT warfarin alone), (3) Send HIT antibody testing. HIT can cause limb loss, stroke, PE, and death.
Evidence Base
RECORD Trials (2008-2009)
- Rivaroxaban 10mg daily superior to enoxaparin for VTE prevention after THA and TKA
- RECORD1 (THA): Total VTE 1.1% vs 3.7% (rivaroxaban vs enoxaparin)
- RECORD3 (TKA): Total VTE 9.6% vs 18.9%
- No significant difference in major bleeding
ADVANCE Trials (2009-2011)
- Apixaban 2.5mg BD non-inferior to enoxaparin 40mg for VTE prevention
- ADVANCE-2 (TKA): Total VTE 15% apixaban vs 24% enoxaparin
- ADVANCE-3 (THA): Total VTE 1.4% vs 3.9%
- Lower major bleeding with apixaban vs enoxaparin
EPCAT II Trial (2018)
- Aspirin 81mg daily non-inferior to rivaroxaban 10mg for extended prophylaxis after THA/TKA
- VTE rates: 0.64% aspirin vs 0.70% rivaroxaban at 90 days
- All patients received rivaroxaban for first 5 days postoperatively
- Similar bleeding rates between groups
PREPIC-2 Trial (2015)
- Retrievable IVC filter + anticoagulation vs anticoagulation alone in PE patients
- No reduction in recurrent PE at 3 months (3.0% vs 1.5%, p=0.5)
- Higher DVT rate in filter group at 3 months (5.9% vs 2.6%)
- Filters showed no mortality benefit
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: VTE Prophylaxis Protocol for THA
"A 68-year-old woman is scheduled for elective total hip arthroplasty for osteoarthritis. She has well-controlled hypertension and type 2 diabetes. What is your VTE prophylaxis strategy?"
Scenario 2: Suspected PE Postoperatively
"A 72-year-old man is 5 days post total knee arthroplasty. He develops sudden onset dyspnea, pleuritic chest pain, and is tachycardic at 110 bpm. SpO2 is 88% on room air. What is your management?"
Scenario 3: Contraindication to Anticoagulation
"A 58-year-old man with hip fracture also has active GI bleeding from a peptic ulcer. He requires surgery within 24-48 hours. How do you manage VTE prophylaxis?"
Australian Context
Australian Guidelines and Resources:
VTE prophylaxis in Australia is guided by multiple authoritative sources that should inform clinical practice and are relevant to FRACS examinations.
Therapeutic Guidelines (eTG): The Antibiotic (eTG) and Cardiovascular (eTG) guidelines provide evidence-based recommendations for VTE prophylaxis and treatment in the Australian context. Key recommendations align with international guidelines including ACCP, with emphasis on:
- Risk stratification for all surgical patients
- Mechanical and chemical prophylaxis for high-risk orthopaedic procedures
- Extended prophylaxis (35 days) for THA, TKA, and hip fracture surgery
- LMWH or DOAC as first-line agents
NHMRC Patient Blood Management Guidelines: Module 2 (Perioperative) includes recommendations on VTE prophylaxis as part of comprehensive perioperative care. The guidelines emphasize individualized risk assessment and multimodal prophylaxis.
Australian Commission on Safety and Quality in Health Care: VTE prevention is a national clinical care standard. All hospitals must:
- Perform VTE risk assessment on admission
- Document prophylaxis plan
- Monitor compliance with prophylaxis protocols
- Report VTE as a hospital-acquired complication
PBS-Listed Agents (Pharmaceutical Benefits Scheme): The following agents are PBS-listed for VTE prophylaxis after orthopaedic surgery in Australia:
- Enoxaparin (Clexane) - first-line LMWH
- Rivaroxaban (Xarelto) - PBS streamlined for THA, TKA prophylaxis
- Apixaban (Eliquis) - PBS listed for THA, TKA prophylaxis
- Aspirin - available OTC, used for extended prophylaxis
Quitline (13 7848) and Smoking Cessation: Smoking is an independent risk factor for VTE. Preoperative smoking cessation counseling should be provided, and patients can be referred to Quitline for support. Smoking cessation for 4 or more weeks preoperatively reduces complications including VTE.
Australian VTE Prevention
The Australian Commission on Safety and Quality in Health Care includes VTE as a key hospital-acquired complication for reporting. This means hospitals track VTE rates and compliance with prophylaxis protocols. Understanding the medicolegal and quality improvement aspects of VTE prevention is important for FRACS candidates.
VENOUS THROMBOEMBOLISM - COMPREHENSIVE
High-Yield Exam Summary
Virchow's Triad (SHE)
- •Stasis: Immobility, venous pooling - treat with mechanical prophylaxis, early mobilization
- •Hypercoagulability: Trauma, surgery, inherited thrombophilia - treat with chemical prophylaxis
- •Endothelial injury: Surgery, fractures, cement - minimize with gentle technique
- •All three present in major orthopaedic surgery - explains high VTE risk
Risk Stratification (Caprini)
- •Score 0: Very low risk (0.5%) - early ambulation only
- •Score 1-2: Low risk (1.5%) - mechanical prophylaxis
- •Score 3-4: Moderate risk (3%) - mechanical + chemical prophylaxis
- •Score 5+: High risk (6%) - mechanical + chemical + extended prophylaxis (35 days)
- •5-point factors: Hip/pelvis/leg fracture, prior VTE, stroke, spinal cord injury, arthroplasty
Chemical Prophylaxis Agents
- •Enoxaparin: 40mg SC daily, start 12-24h postop, gold standard LMWH
- •Rivaroxaban: 10mg PO daily, start 6-10h postop, Factor Xa inhibitor
- •Apixaban: 2.5mg PO BD, start 12-24h postop, renal-safe DOAC
- •Aspirin: 100-300mg daily, acceptable for extended phase or lower-risk patients
- •All THA/TKA/hip fracture: 35 days extended prophylaxis (ACCP Grade 1B)
DVT Diagnosis
- •Wells Score: 3+ = high probability (53% prevalence)
- •D-dimer: DO NOT use postoperatively (always elevated)
- •Compression ultrasound: Gold standard, 95% sensitive for proximal DVT
- •Clinical features: Calf pain, unilateral leg swelling, warmth (CLOT mnemonic)
- •50% of DVTs are asymptomatic
PE Diagnosis and Severity
- •CTPA: Gold standard (95% sensitivity and specificity)
- •Low risk PE: Stable, no RV dysfunction - anticoagulation, consider outpatient
- •Intermediate PE: Stable, RV dysfunction - anticoagulation, close monitoring
- •Massive PE: Hemodynamic instability (SBP less than 90) - thrombolysis, embolectomy, ECMO
- •Biomarkers: Troponin and BNP for risk stratification
Key Timing Points
- •LMWH: 12h before (European) or 12-24h after surgery (North American)
- •Rivaroxaban: 6-10 hours postoperatively
- •Apixaban: 12-24 hours postoperatively
- •Neuraxial: LMWH 12h before and 4h after epidural manipulation
- •DOACs: 24-48h washout before neuraxial procedures
Key Trials
- •RECORD trials: Rivaroxaban superior to enoxaparin for THA/TKA prophylaxis
- •ADVANCE trials: Apixaban non-inferior to enoxaparin with lower bleeding
- •EPCAT II: Aspirin non-inferior to rivaroxaban for extended prophylaxis (after initial DOAC)
- •PREPIC-2: IVC filters do not reduce PE when anticoagulation given
- •SOX trial: Compression stockings showed no PTS benefit (controversial)
Contraindications to Chemical Prophylaxis
- •Active bleeding or high bleeding risk
- •Severe thrombocytopenia (platelets less than 50)
- •Recent intracranial hemorrhage or neurosurgery
- •Epidural/spinal within timing window
- •HIT (for heparin products)
- •If contraindicated: maximize mechanical prophylaxis, consider IVC filter