Deep Vein Thrombosis (DVT) is caused by the formation of a blood clot (thrombus) in the deep veins of the leg. One to three out of 1,000 persons of the general population suffer from DVT every year.
In 1846, Rudolf Virchow described the factors of relevance for the development of DVT. Virchow's Triad still is valid nowadays:
Consequences of DVT
If the thrombus passes to the lungs and obstructs the pulmonary arteries, fatal pulmonary embolism (PE) can be the consequence of DVT. In more than 90% of cases of PE, the thrombosis originates in the deep veins of the leg.
Risk Categories & Contributing Factors
Three major factors contribute to formation of clots in veins:
- Stasis, or slow blood flow through veins. This increases the contact time between blood and vein wall irregularities. It also prevents naturally occurring anticoagulants from mixing in the blood. Prolonged bed rest or immobility promotes stasis.
- Coagulation, which is encouraged by the presence of tissue debris, collagen or fats in the veins. Orthopaedic surgery often releases these materials into the blood system. During hip replacement surgery, reaming and preparing the bone to receive the prosthesis can also release chemical substances (antigens) that stimulate clot formation.
- Damage to the vein walls, which can occur during surgery as the physician retracts, twists, folds or manipulates veins. This can also break intercellular bridges and release substances that promote blood clotting. Other factors that may contribute to the formation of thrombi in the veins include: age, previous history of DVT or PE, metastatic malignancy, vein disease (such as varicose veins), smoking, estrogen usage or current pregnancy, obesity and genetic factors.