What is the cause and treatment of a swollen right knee in a patient with a history of Deep Vein Thrombosis (DVT), pulmonary embolism, and recent thrombectomy?

Post-Thrombectomy Knee Swelling: Diagnosis and Management

The most likely cause of right knee swelling after leg thrombectomy is recurrent or residual DVT in the popliteal or femoral veins, though septic arthritis, hemorrhagic complication, or post-thrombotic venous insufficiency must also be considered. 1, 2

Immediate Diagnostic Approach

Obtain urgent lower extremity venous duplex ultrasound to evaluate for recurrent DVT, as this is the appropriate initial imaging modality for suspected thrombosis in this clinical context. 2 The ultrasound should specifically assess:

• Popliteal vein patency (remember: popliteal DVT is classified as proximal DVT, not distal, and carries high PE risk) 1
• Femoral and iliac vein compressibility 2
• Presence of echogenic thrombus or altered Doppler flow patterns 2
• Signs of venous compression from hematoma 2

Most Likely Differential Diagnoses

1. Recurrent/Residual DVT (Most Likely)

• Thrombectomy does not eliminate the underlying prothrombotic state in patients with extensive VTE history 3, 4
• Incomplete thrombus removal or early rethrombosis occurs despite mechanical intervention 3, 5
• This patient's multiple VTE risk factors (HIV, vascular insufficiency, prior DVT/PE) create persistent hypercoagulability 6

2. Post-Procedural Hematoma with Venous Compression

• Large hematomas compress adjacent deep veins, causing venous stasis and reduced blood flow (Virchow's triad) 2
• The inflammatory milieu from tissue injury creates a prothrombotic environment 2
• Hemorrhagic injury itself increases compartment syndrome and thrombotic complication risk 2

3. Septic Arthritis (Less Likely but Critical to Exclude)

• Septic knee can induce DVT through inflammatory mechanisms 7
• This patient's immunocompromised state (HIV) increases infection risk 7
• Perform arthrocentesis if fever, warmth, or severe pain present 7, 8

Treatment Algorithm

If DVT Confirmed on Ultrasound:

Immediately restart therapeutic anticoagulation - this is mandatory for all proximal DVTs (including popliteal). 6, 1

Anticoagulation options (in order of preference):

1. Low-molecular-weight heparin (LMWH) - preferred first-line agent 6, 1
2. Fondaparinux - alternative to LMWH 6, 1
3. Unfractionated heparin (IV or SC) - use if severe renal impairment (this patient has multiple comorbidities that may affect renal function) 6, 1

Duration of anticoagulation:

• Minimum 3 months for all proximal DVTs 6, 1
• Consider extended (indefinite) anticoagulation given this patient's unprovoked recurrent VTE history and low-moderate bleeding risk 6
• Proximal DVT recurrence rate is 10.3 events per 100 person-years after stopping anticoagulation 1

Critical Management Pitfalls to Avoid:

• Never withhold anticoagulation for confirmed proximal DVT - untreated proximal DVT carries 25-30% mortality from PE 1
• Do not assume thrombectomy provides definitive treatment - anticoagulation duration is the same whether or not thrombectomy was performed 6
• Initiate thromboprophylaxis within 6-36 hours after hemorrhage control if hematoma is the primary issue 2

Adjunctive Measures:

• Compression stockings (30-40 mmHg knee-high) for 2 years to reduce post-thrombotic syndrome risk by 50% 6
• Early ambulation once acute pain/edema improves 6
• Elevate affected limb to reduce swelling 8

If Ultrasound Negative for DVT:

• Aspirate knee joint if septic arthritis suspected (immunocompromised patient with HIV) 7, 8
• Send synovial fluid for cell count, Gram stain, culture 7, 8
• Consider MRI if structural abnormality suspected (meniscal tear, ligamentous injury from procedure) 8
• Treat symptomatically with NSAIDs, ice, elevation if inflammatory etiology 8

Special Considerations for This Patient

Given this patient's extensive thrombotic history (DVT, PE, blood clots in legs/lungs) and multiple comorbidities, the threshold for extended anticoagulation should be very low. 6 The American Society of Hematology suggests extended therapy for unprovoked proximal DVT with low-moderate bleeding risk. 6 This patient's recurrent VTE pattern strongly suggests underlying thrombophilia or persistent risk factors requiring indefinite anticoagulation. 6

Monitor closely for hemodynamic compromise given history of pulmonary embolism - any chest pain, dyspnea, or tachycardia warrants immediate PE evaluation. 6