## Most Common Site of Venous Thrombosis ### Epidemiology Deep vein thrombosis (DVT) of the lower limbs accounts for approximately 90% of all venous thrombotic events. This is the classic presentation of venous thromboembolism (VTE). ### Why the Lower Limbs? **Key Point:** The deep veins of the lower limb are the most common site because of: 1. **Venous stasis** — gravity and prolonged immobility (bed rest, long flights, surgery) cause blood pooling in dependent veins 2. **Large vessel calibre** — femoral, popliteal, and calf veins are large-bore vessels where flow is naturally slower 3. **Valve incompetence** — venous valves in the legs are prone to dysfunction, especially after injury 4. **Endothelial injury risk** — trauma, surgery, and catheterization commonly affect leg veins ### Virchow's Triad in Lower Limb DVT | Component | Mechanism | Example | |-----------|-----------|----------| | Stasis | Immobility, obesity, heart failure | Bed rest, long-haul flights | | Endothelial injury | Trauma, surgery, catheterization | Hip replacement, femoral line | | Hypercoagulability | Malignancy, thrombophilia, OCP | Cancer, Factor V Leiden | **High-Yield:** The **popliteal and femoral veins** are the most frequent sites within the lower limb, followed by calf veins (soleal and gastrocnemius). ### Clinical Significance Lower limb DVT carries the highest risk of pulmonary embolism (PE), making it the most clinically important site of thrombosis. **Clinical Pearl:** Unilateral leg swelling, pain, and warmth in a post-operative or immobilized patient should raise immediate suspicion for lower limb DVT; compression ultrasound is the gold standard for diagnosis.
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