A deep venous thrombosis is caused by the abnormal formation of a blood clot in the vein.

Factors that lead to deep vein thrombosis include:

• Injury to the wall of a vein
• Slowed blood flow
• Blocked blood flow
• Blood clotting disorder

Conditions that may lead to deep vein thrombosis include:

• Birth control pills that contain estrogen
• Blood clotting disorders
• Cancer
• Leg fracture
• Hip fracture
• Heart failure
• Prolonged bed rest
• Prolonged periods of sitting, such as during travel
• Recent childbirth
• Severe obesity
• Smoking
• Surgery on the brain, neck, back or abdomen
• Surgery on the bones in the hips or legs
• Knee joint replacement
• Hip joint replacement
• Recent heart attack
• Use of a wheelchair