A blood clot behind your knee can cause swelling and pain. It can become serious if not treated.

The popliteal vein runs up the back of the knee and carries blood from the lower leg to the heart. Sometimes, a blood clot, or a thrombosis, can block this important vein. This is known as deep vein thrombosis (DVT).

A blood clot behind your knee can restrict circulation in your legs, which can damage blood vessels and surrounding tissue.

A clot can also break loose and travel to the right side of the heart and to the lungs, where it can cause severe circulation and respiratory problems, and strokes.

Keep reading to learn the symptoms and treatment for this type of blood clot and how to lower your risk of developing it.

You can have a blood clot without any apparent symptoms. When symptoms occur, they can include:

  • pain, which may feel like a cramp
  • swelling, or having one leg look bigger than the other
  • tenderness
  • warmth, where the skin of the affected area feels warm to the touch

A blood clot can be an emergency

A blood clot in your circulatory system can cause a pulmonary embolism. If it reaches the brain, it can cause a stroke. If a clot is lodged in one of the arteries supplying blood to the heart muscle, the result can be a heart attack.

If you experience symptoms of these conditions, call 911 or your local emergency services. Symptoms can include:

  • difficulty breathing
  • chest pain
  • changes in speech or your ability to understand speech
  • facial drooping
  • confusion
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People with a Baker’s cyst typically have severe inflammation in the knee that leads to joint effusion, or excessive water on the back of the knee. It may develop due to severe inflammation relating to:

  • inflammatory conditions, such as rheumatoid arthritis or osteoarthritis
  • injury
  • arthritis

It can cause symptoms, including swelling and pain behind the knee, that may be similar to popliteal vein thrombosis.

The swelling caused by a Baker’s cyst may be reduced when the knee is flexed to 45 degrees. The pain may also feel worse with activity.

A doctor can perform tests to distinguish between the two conditions.

Popliteal vein thrombosis and other forms of DVT can result from vein damage or if your legs are still for a long time.

Damage to your vein can occur due to:

  • smoking cigarettes
  • drug use
  • a major injury
  • chronic inflammation, which injures the inner lining of your vein
  • recent surgery to the limb, such as surgery for an ankle fracture, total knee replacement, total hip replacement, or hip fracture)

When your legs are still for prolonged periods, and you’re not on your feet walking and moving around, blood flow in the legs gets sluggish. When blood isn’t circulating as it should, it can pool in a part of your vein and form a clot.

If you are immobile, such as while in the hospital or after surgery, leg compression stockings or a compression machine may reduce your chance of developing blood clots.

You may have an increased risk for DVT if you cannot move around since this can affect blood flow to your legs.

Risk factors for popliteal vein thrombosis can include:

  • recent surgery
  • tobacco use
  • having obesity
  • taking estrogen, whether as birth control or hormone replacement therapy
  • having DVT in the past
  • not being able to move around
  • history of cancer or active cancer
  • lower extremity trauma
  • family history of blood clots

Pregnancy can also temporarily increase your risk of blood clots.

DVT also tends to occur more often in people over age 40 and people assigned male at birth.

Factor V Leiden

Another risk factor is an inherited health condition called factor V Leiden. It’s a mutation of one of the proteins that help control bleeding and clotting. It can increase your risk of abnormal clots, but you may have factor V Leiden and never experience clotting problems.

If you develop popliteal vein thrombosis or another form of DVT and have a family history of clotting issues, a doctor may recommend testing for factor V Leiden. A blood test and a genetic test can help a doctor determine whether you have this inherited condition.

A sudden onset of swelling, tenderness, and pain in the leg could indicate that you have a DVT. If the discomfort and swelling are in the area behind the knee, it may be a popliteal vein thrombosis.

Diagnosis of a blood clot behind the knee can include multiple exams and tests, such as:

  • physical exam
  • ultrasound of your leg and knee
  • venogram, which is an X-ray using a dye to help doctors see your veins more clearly
  • D-dimer test, which tests your blood for a substance released by blood clots

Treatment for popliteal vein thrombosis can include medication, procedures, and methods to improve blood circulation.


Anticoagulants, or blood thinners, can prevent blood clots from forming. Some examples include:

  • aspirin (Bayer)
  • heparin and warfarin (Coumadin, Jantoven)
  • rivaroxaban (Xarelto)
  • apixaban (Eliquis)
  • dabigatran (Pradaxa)
  • enoxaparin (Lovenox)

Anticoagulants and your body’s defenses may help a clot dissolve over time. Using aspirin for a longer period may also help reduce the risk of new clots forming in your veins.


Depending on where the clot is located and how serious it is, a doctor may need to remove it. They can use special catheters, but this isn’t always an option. Sometimes, they may place a filter to prevent large clots from reaching the heart.

Clots that are especially difficult to reach may require surgery.

Lifestyle methods

Wearing compression stockings can also improve blood circulation in your lower legs.

A doctor may also recommend physical activity or stretching your legs to improve circulation.

Popliteal vein thrombosis is serious but can often be managed or treated if diagnosed in time.

With treatment, there aren’t usually any long-term consequences. A doctor may recommend preventive measures to reduce the risk of developing another clot. You may also have to use anticoagulant medication for the rest of your life.

Without treatment, a blood clot can be life threatening.

Because surgery and prolonged bed rest can lead to DVT, moving around after surgery, once it is safe to do so, can reduce your risk.

Other ways to help prevent popliteal vein thrombosis and other forms of DVT can include:

  • If you’re sedentary during the day, try to move around more often. If you have trouble walking, try standing or moving your legs from a seated position.
  • Take medications, especially anticoagulants, as prescribed.
  • If you’re at risk for DVT, a doctor may suggest you wear compression stockings regularly.
  • If you use tobacco, consider quitting. Tobacco use can increase your risk.
  • Maintaining a moderate weight may help reduce your risk. A doctor may recommend a specific eating plan, medication, or regular physical exercise.

A blood clot behind your knee can cause symptoms like swelling and discomfort. It can be life threatening if not treated. If you think you may have a blood clot, visit the emergency room. Doctors can rule out a blood clot noninvasively with an ultrasound.

Treatment may include blood thinners or a medical procedure.