Popliteal artery entrapment syndrome (PAES) is an uncommon condition in which an abnormally positioned or enlarged calf muscle presses on the main artery behind the knee (popliteal artery). The artery becomes trapped, making it harder for blood to flow to the lower leg and foot.

Popliteal artery entrapment syndrome is most common among athletes.

The main symptom of popliteal artery entrapment syndrome (PAES) is pain or cramping in the back of the lower leg (the calf) that occurs during exercise and goes away with rest. Other signs and symptoms may include:

• Cold feet after exercise
• Tingling or burning in your calf (paresthesia)
• Numbness in the calf area

If the nearby vein (popliteal vein) also becomes trapped by the calf muscle, you may have:

• Heavy feeling in the leg
• Lower leg cramping at night
• Swelling in the calf area
• Changes in skin color around the calf muscle
• Blood clots in the lower leg (deep vein thrombosis)

Symptoms typically affect young, otherwise healthy people under age 40.

When to see a doctor

See your doctor if you have any type of leg pain, especially if you have calf or foot cramping during activity that gets better with rest.

Popliteal artery entrapment syndrome (PAES) is caused by an abnormal calf muscle, usually the gastrocnemius muscle.

The condition may occur from birth (congenital) or develop later in life (acquired). In the congenital form, the calf muscle or nearby artery is abnormally positioned while the baby grows in the mother's womb. People with the acquired form of PAES have a calf muscle that is bigger than normal (enlarged).

The abnormal calf muscle presses on the main artery behind the knee (popliteal artery), reducing blood flow to the lower leg. The lack of blood flow results in pain and cramping in the back of the lower leg during times of activity.

Popliteal artery entrapment syndrome (PAES) is uncommon. The following things increase your risk of the condition.

• Younger age. The condition is most often seen in people who are in their late teens or 20s. It's rarely diagnosed in those over age 40.
• Being male. PAES can occur in anyone, but it's much more common in young men.
• Strenuous athletic activity. Runners, bicyclists, and athletes who try to build muscle fast with weight training routines or high-intensity circuit training are at the highest risk.

Long-term pressure on the popliteal artery can cause the artery to narrow (stenosis), causing pain and cramping with just slight activity, such as walking.

In severe cases or when undiagnosed, the nerves and muscles in the leg can become damaged. Blood clots may occur in the lower leg (deep vein thrombosis). Older athletes with signs and symptoms of popliteal artery entrapment syndrome should be checked for popliteal aneurysm, which is common in older men.

Your doctor will carefully examine you and ask questions about your symptoms and health history. However, because most people with popliteal artery entrapment syndrome (PAES) are young and usually healthy, diagnosing the condition can sometimes be challenging. The findings from a physical exam usually are normal.

Your doctor will rule out other causes of leg pain, including muscle strains, stress fractures, chronic exertional compartment syndrome and peripheral artery disease, which results from clogged arteries.

Tests used to rule out other conditions and diagnose PAES include the following:

• Ankle-brachial index (ABI) measurement is usually the first test done to diagnose PAES. Blood pressure measurements are taken in your arms and legs during and after walking on a treadmill. The ABI is determined by dividing ankle pressure by arm pressure. The blood pressure in your legs should be higher than that in your arms. But if you have PAES, your ankle pressure drops during exercise.
• Duplex ultrasound of the calf uses high-frequency sound waves to determine how fast blood is flowing through the leg arteries. This noninvasive test may be done before or after exercise or while you flex your foot up and down, which puts your calf muscle to work.
• Magnetic resonance angiography (MRA) shows the calf muscle that is trapping the artery. It can also reveal how much of the popliteal artery is narrowed. You may be asked to flex your foot or press it against a board during this test. Doing so helps your doctor determine how blood is flowing to your lower leg.
• CT angiography also shows which leg muscle is causing the artery entrapment. As with MRA, you may be asked to change the position of your foot during this test.
• Catheter-based angiography allows your doctor to see how blood is flowing to and from the lower leg in real time. It's done if the diagnosis is still unclear after other, less invasive imaging tests.

Surgery is the only way to correct the abnormal calf muscle and free the trapped artery. Your doctor will likely recommend surgery if your symptoms significantly affect your everyday or athletic activities.

During surgery, the surgeon makes an incision on the inner calf just below the knee, or in the back of the knee, to release the abnormal calf muscle and give the artery more room. This will prevent the calf muscle from pressing on the artery in the future. Surgery is done while you are under general anesthesia. The procedure takes about an hour. Typically, you'll need to stay in the hospital for one day.

If you've had the condition for a long time, you may need artery bypass surgery. Bypass surgery is usually done only on those who have severe narrowing of the artery (stenosis) due to long-term popliteal artery entrapment syndrome.

Surgery to release the calf muscle and artery usually doesn't affect leg function. When the condition is diagnosed and treated early, a full recovery is expected, and your symptoms should disappear.

If you think you may have popliteal artery entrapment syndrome, it's important that you make an appointment with your doctor. If popliteal artery entrapment syndrome is found early, your treatment may be easier and more effective.

Because appointments can be brief, and because there's often a lot to discuss, it's a good idea to be prepared for your appointment. Here's some information to help you get ready for your appointment and know what to expect from your doctor.

What you can do

• Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance, such as not drinking or eating anything for a few hours. You may need to do this if your doctor orders blood tests.
• Write down any symptoms you're having, including any that may seem unrelated to popliteal artery entrapment syndrome.
• Write down key personal information, including any family history of heart disease, stroke, high blood pressure or blood clots, and any major stresses or recent life changes.
• Make a list of all medications, vitamins or supplements that you're taking.
• Take a family member or friend along, if possible. Sometimes it can be difficult to understand and remember all the information received during an appointment. The person who goes with you may remember something that you missed or forgot.
• Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions will help you make the most of your time together. List your questions from most important to least important, in case time runs out. For popliteal artery entrapment syndrome, some basic questions to ask your doctor include:

• What is likely causing my symptoms or condition?
• What are other possible causes for my symptoms or condition?
• What kinds of tests will I need?
• What's the most appropriate treatment?
• What's an appropriate level of physical activity?
• What are the alternatives to the primary approach that you're suggesting?
• I have other health conditions. How can I best manage them together?
• Are there any restrictions that I need to follow?
• Are there any brochures or other printed material that I can take home with me? What websites do you recommend visiting?

Don't hesitate to ask your doctor additional questions during your appointment.

What to expect from your doctor

Your doctor is likely to ask you a number of questions. Being ready to answer them may save time to go over any points you want to spend more time on. Your doctor may ask:

• When did you first start having symptoms?
• Do you always have symptoms or do they come and go?
• How severe are your symptoms?
• What, if anything, seems to make your symptoms better?
• What, if anything, makes your symptoms worse?