What Are the Symptoms of a Blood Clot in the Knee?

Unrestricted blood flow is critical to maintain proper function of the body. Any blockage of veins or arteries will cause a backup that can endanger not only the blocked area, but the entire pulmonary system. Limbs can swell up, organs may function improperly and cells and tissue that need the oxygen and nutrients that blood flow provides will begin to breakdown. Coagulation is important for controlling blood flow, as in the instance of an open wound, but a blood clot can travel to the lungs or the heart and become life-threatening.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.

General Causes

Formation of a blood clot (thrombosis) can be caused by obesity, paralysis, major surgery or major injury, immobility, varicose veins, heart disease and cancer.cause:

  • Formation of a blood clot (thrombosis) can be caused by obesity
  • paralysis
  • major surgery or major injury
  • immobility
  • varicose veins
  • heart disease
  • cancer

Women who use birth control pills may be at risk of developing a more serious deep vein thrombosis (DVT), and it has been reported that estrogen therapy may increase the risk of developing blood clots, although conclusive medical findings are still being investigated.

Causes of Blood Clots on the Knee

According to the National Library of Medicine a blood clot may form in the knee area for a variety of reasons 1. Age can be a factor, and the chance of developing a blood clot can increase two-fold in each decade for people over the age of 40. Other causes of blood clots on the knee include: prolonged bed rest or long periods of sitting and lying down, leg paralysis any major surgery under general anesthesia (especially involving hips or legs), and trauma to the knee area from a blow or fall.


There is a difficulty in diagnosing small blood clots, especially below the knee. Most will go undetected because they do not cause any obvious swelling or pain. It is not until a DVT occurs above the knee that symptoms will appear, and then it becomes crucial to begin treatment for the clotting. The most common signs of a DVT are a noticeable swelling of the leg, a warmth or a redness in the area surrounding the knee (the calf or the thigh area), and leg pain that seems to worsen when standing or walking.


A physician may conduct a variety of tests if a DVT is suspected in the knee area. These tests include: the d-Dimer test (a blood test to determine the likelihood of a DVT in the bloodstream), an ultrasound scan, the taking of blood samples to test for genetic or biochemical tendencies for developing a blood clot, or a venogram, which is considered to be the best way to confirm a DVT. This test requires a dye injection into the bloodstream, and there may be some complications such as discomfort and an increased chance of clotting.


According to the Society of Vascular Surgery anti-coagulants, such as heparin or low molecular weight heparin (LMWH), may be injected to help clots from forming and warfarin will then be taken orally for a period of between three to 12 months, depending on the patient’s reactions to the treatment. An injection of a thrombolysis may be required to dissolve the clot. Surgery may be needed if these other methods do not work, including implanting a vena cava filter in the abdomen area to prevent blood clots from reaching the lungs.