Cause

Three factors can increase the risk of deep vein thrombosis:

• Slowed blood flow. If you have surgery or are inactive for a period of time (for example, if you are bedridden or must sit while on a long flight or car trip), blood flow in your legs is slowed, which allows a blood clot to form.
• Damage to the blood vessels. Surgery or injury may damage your blood vessels.
• Changes in the blood itself. Cancer or certain inherited factors may cause your blood to clot more quickly than normal.