The Popliteal Fossa: Naming the Back of Your Knee

More Health Education Articles

The Popliteal Fossa: Naming the Back of Your Knee

By Your Health Magazine Health Information Team

You stand up after sitting for a while and notice tightness in the hollow behind your knee. Or perhaps you feel a small lump there and realize you are not sure what that part of the body is called. So, what do you call the back of the knee? The anatomical term is the popliteal fossa, a shallow, diamond-shaped space located behind the knee joint.

The popliteal fossa is more than a simple crease in the skin. It is a passageway for important blood vessels, nerves, muscles, tendons, lymph nodes, and other tissues involved in moving and supplying the lower leg. Understanding this area can make it easier to describe symptoms accurately and recognize when pain or swelling deserves medical attention.

What Is the Popliteal Fossa?

In anatomy, a “fossa” is a hollow or depressed area. “Popliteal” refers to the region behind the knee. Together, the term popliteal fossa describes the soft space you can feel when your knee is slightly bent.

The edges of this space are formed primarily by the hamstring muscles above and the calf muscles below. Deeper inside are the back portion of the knee joint, connective tissues, and the popliteus muscle, which assists with knee movement and stability.

Several major structures pass through the popliteal fossa:

• The popliteal artery, which supplies blood to the knee and lower leg
• The popliteal vein, which carries blood back toward the heart
• The tibial and common fibular nerves, which help control movement and sensation in the lower leg and foot
• Tendons from the hamstring and calf muscles
• Popliteal lymph nodes and lymphatic vessels

Because so many structures are concentrated in a relatively small area, discomfort behind the knee may come from the joint itself, nearby muscles and tendons, a fluid-filled cyst, or, less commonly, a blood vessel or nerve problem.

Why Might the Back of the Knee Hurt?

Posterior knee pain can feel like an ache, pulling sensation, pressure, stiffness, or sharp pain. Some people notice symptoms only when bending the knee, climbing stairs, running, or rising from a chair. Others may have swelling or discomfort even at rest.

Muscle or Tendon Strain

The hamstrings cross the back of the knee from above, while the gastrocnemius calf muscle begins just below the joint. Sudden acceleration, jumping, overuse, or an awkward step can strain these tissues. The discomfort may worsen when straightening the leg, bending the knee against resistance, or stretching the hamstrings or calf.

Baker Cyst

A Baker cyst, also called a popliteal cyst, is a collection of joint fluid that forms behind the knee. It may feel like a soft, fluid-filled lump and can cause tightness, stiffness, or difficulty bending the joint. Some Baker cysts cause few or no symptoms.

These cysts often develop when another knee problem, such as arthritis, cartilage damage, or a meniscus injury, causes excess joint fluid. Treating the underlying knee condition is therefore an important part of care. A cyst can occasionally rupture, producing pain and swelling that extend into the calf.

Arthritis and Joint Inflammation

Osteoarthritis and inflammatory forms of arthritis can cause pain, swelling, and stiffness throughout the knee, including the popliteal area. Symptoms may be more noticeable after inactivity or prolonged use. Joint inflammation may also contribute to the development of a Baker cyst.

Meniscus or Ligament Injury

The menisci are cartilage structures that cushion and stabilize the knee. A tear involving the back portion of a meniscus may produce pain toward the rear or side of the joint. Swelling, catching, locking, or a feeling that the knee may give way can also occur. Ligament injuries, including injuries to the posterior cruciate ligament, may cause pain deeper in the knee after a fall, collision, or forceful twisting movement.

For a closer look at possible causes and management options, read this guide to relieving pain in the back of your knee.

Blood Clot

A deep vein thrombosis, or DVT, is a blood clot in a deep vein. A clot in the leg may cause swelling, tenderness, warmth, redness, or discoloration. Symptoms can resemble those of a ruptured Baker cyst, and appearance alone cannot reliably distinguish the two.

A DVT requires prompt medical evaluation because part of the clot can travel to the lungs and cause a pulmonary embolism. This is one reason sudden, unexplained swelling behind the knee or in the calf should not be self-diagnosed.

How Is a Popliteal-Area Problem Evaluated?

A healthcare professional will usually ask when symptoms began, whether an injury occurred, and which activities make the problem better or worse. The examination may include checking the knee’s range of motion, stability, swelling, tenderness, skin temperature, circulation, and sensation.

Imaging depends on the suspected cause. An X-ray can reveal arthritis, fractures, and certain bone changes but does not show every soft-tissue injury. Ultrasound may be used to examine a lump, identify a Baker cyst, or check blood flow when a clot is a concern. MRI can provide detailed images of the menisci, ligaments, tendons, cartilage, and other soft tissues.

What Can You Do About Mild Discomfort?

For mild symptoms that clearly began after increased activity and are not accompanied by significant swelling or instability, temporarily reducing the aggravating activity may help. A wrapped cold pack may ease short-term soreness and swelling. Gentle movement can prevent unnecessary stiffness, but painful stretching, running, or heavy exercise should not be forced.

Treatment should match the cause. Depending on the diagnosis, a clinician may recommend physical therapy, exercises to improve strength and flexibility, medication, treatment for arthritis, drainage of a symptomatic cyst, or evaluation by an orthopedic specialist. Surgery is not routinely needed for uncomplicated discomfort or most Baker cysts.

For additional general education about symptoms and medical conditions, visit the MedlinePlus health topics library.

When to Seek Care

Schedule an appointment with a primary care clinician, sports medicine physician, or orthopedic specialist if pain lasts, repeatedly returns, limits walking or knee movement, or follows an injury. Evaluation is also appropriate for a new lump, ongoing stiffness, joint locking, instability, numbness, or swelling that does not improve. A physical therapist may assist with rehabilitation after a clinician has identified the likely cause.

Seek prompt medical care for sudden one-sided leg swelling, warmth, redness, or unexplained calf or knee pain, especially after surgery, prolonged immobility, or a long period of travel. Call emergency services for shortness of breath, chest pain, fainting, a rapid or irregular heartbeat, or coughing up blood. Urgent evaluation is also warranted after a major injury if the knee appears deformed, cannot bear weight, becomes rapidly swollen, or the foot turns pale, cold, numb, or weak.

A Useful Name for an Important Area

The next time someone asks, “What do you call the back of the knee?” the answer is the popliteal fossa. Knowing the term can help you explain exactly where you feel pain, pressure, or swelling. Most minor discomfort in this region is related to muscles, tendons, or the knee joint, but sudden or persistent symptoms should be evaluated because the area also contains major nerves and blood vessels.