Popliteal Artery Entrapment Syndrome (PAES)
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Popliteal artery entrapment syndrome (PAES) is a rare condition that occurs when the popliteal artery, the main artery running from the thigh to the calf, is compressed by an enlarged or improperly positioned calf muscle behind the knee. The gastrocnemius muscle, which attaches to the thigh bone, can cause this compression when it contracts during foot plantar flexion, making it difficult for blood to flow to the lower leg and foot.
Repetitive compression during exercise can cause spasms in your arteries, which can reduce blood flow. As a result, lactic acid and carbon dioxide can build up in your muscles and nerves, leading to sensations of fatigue, achiness, heaviness, and, in some cases, numbness in your calf and foot.
After stopping the exercise, the symptoms usually show improvement within three to five minutes. However, if left untreated, the spasm tends to happen more quickly and persist for a longer duration over time. The symptoms also tend to occur after covering a shorter distance, and the recovery time increases.
Symptoms
PAES typically presents with discomfort or cramping in the posterior lower leg (calf) that arises during physical activity and subsides after a period of rest. Additional warning signs and symptoms could be:
- The calf has numbness
- The feet feels cold after exercise
- Paresthesia, characterized by a tingling or burning sensation in the calf muscle
In case the calf muscle entraps the popliteal vein nearby, the symptoms you may experience include:
- The leg feels heavy
- Cramps of the lower legs in the evening
- Swollen or discolored calf
- The lower leg has clots of blood, also called Deep Vein Thrombosis (DVT)
Leg pain symptoms generally tend to impact individuals who are under the age of 40 and in good health. It is advisable to seek medical attention from your doctor if you experience any type of leg pain, particularly if you experience cramping in your calf or foot during physical activity that subsides after rest.
Causes
Popliteal artery entrapment syndrome (PAES) is a medical condition that occurs when the calf muscle, particularly the gastrocnemius muscle, abnormally presses on the main artery located at the back of the knee known as the popliteal artery. This pressure reduces blood flow to the lower leg, resulting in pain and cramping in the back of the lower leg during times of physical activity. The condition may either be present at birth (congenital) or develop later in life. In congenital PAES, the calf muscle or adjacent artery is positioned abnormally during fetal development. Meanwhile, acquired PAES is characterized by an enlarged calf muscle that can press on the popliteal artery.
Risk factors
Popliteal artery entrapment syndrome (PAES) is a relatively rare medical condition. However, certain factors may increase your likelihood of developing it, including:
- Age. PAES is commonly seen in individuals in their late teens or 20s and is rarely diagnosed in those over the age of 40.
- Gender. Although PAES can happen to anyone, and is more prevalent in young men.
- Sports activity. People who engage in activities such as running, cycling, and weight training routines that require the use of the lower extremities and muscles are at a higher risk of developing PAES.
Diagnosis
When a patient presents with symptoms of popliteal artery entrapment syndrome (PAES), their doctor will conduct a thorough examination and inquire about their medical history. Due to the fact that PAES is most commonly observed in young and healthy individuals, diagnosing the condition can be difficult. Physical examination results may not indicate any abnormalities.
The doctor will eliminate other potential causes of leg pain, such as muscle strains, stress fractures, chronic exertional compartment syndrome, and peripheral artery disease. Peripheral artery disease is caused by the blockage of arteries.
To diagnose PAES, several tests are used to rule out other conditions and confirm the diagnosis:
- Ankle-Brachial Index (ABI). This is the first test used to diagnose PAES. During this test, blood pressure readings are taken in both your arms and legs before and after walking on a treadmill. The ankle pressure is then divided by the arm pressure to determine the ABI. Typically, the blood pressure in your legs should be higher than that in your arms, but if you have PAES, your ankle pressure may drop during exercise.
- Duplex ultrasound of the calf. This test uses high-frequency sound waves to measure the speed of blood flow in the leg arteries. The ultrasound may be performed before or after exercise or while you flex your foot up and down to engage the calf muscle.
- Magnetic Resonance Angiography (MRA). The calf muscle that is trapping the artery is shown. It can also show how much of the popliteal artery is blocked. During this test, you may be asked to flex your foot or press it against a board. This allows your doctor to determine how much blood is flowing to your lower leg.
- Computed Tomography (CT) angiography. This demonstrates which leg muscle is causing the artery entrapment. During this test, you may be asked to change the position of your foot, as with MRA.
- Catheter-based angiography. This shows your doctor how blood flows to and from your lower leg in real time. It is performed if the diagnosis remains ambiguous after other, less invasive imaging tests.
Treatment
When an abnormal calf muscle compresses an artery and causes symptoms that significantly affect your daily life or athletic activities, surgery is often recommended. During the surgical procedure, which typically takes about an hour and is performed under general anesthesia, 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 provide more space for the artery. This prevents the calf muscle from compressing the artery in the future. Hospitalization for a day is usually required after the surgery.
In cases where the condition has persisted for a long time, artery bypass surgery may be necessary to treat severe narrowing of the artery caused by long-term popliteal artery entrapment syndrome. For the functional type of PAES, injections of Botulinum toxin A are the only non-surgical treatment available. Your healthcare provider will use CT or ultrasound guidance to inject Botox or Dysport into the muscle responsible for compression. This will temporarily paralyze the muscle in the hopes of causing it to shrink permanently.
However, this effect is short-lived and typically only lasts between three to six months. If the muscle does not shrink, symptoms will return. Success rates for this treatment have been reported to be less than 60% after one year.
