Popliteal artery entrapment syndrome

In 1879, the syndrome was first described in a 64 years old male by Anderson Stuart, a medical student. In 1959, Hamming and Vink first described the management of the PAES in a 12-year-old patient. The patient was treated with myotomy of the medial head of the gastrocnemius muscle and concomitant endarterectomy of the popliteal artery. They later reported four more cases and claimed that the incidence of this pathology in patients younger than 30 years old with claudication was 40%. Servello was the first to draw attention to diminished distal pulses observed with forced plantar- or dorsiflexion in patients with this syndrome. In 1981, Bouhoutsos and Daskalakis reported 45 cases of this syndrome in a population of 20,000 Greek soldiers. Over the last few decades, the increasing frequency with which popliteal artery entrapment is reported, strongly suggests greater awareness of the syndrome. == Epidemiology ==

In the general population, popliteal artery entrapment syndrome (PAES) has an estimated prevalence of 0.16%. It is most commonly found in young, physically active males. In fact, sixty percent of all cases of this syndrome occur in athletically active males under the age of 30. The predilection of this syndrome presents in a male to female ratio of 15:1. People, who participate in running, soccer, football, basketball, or rugby, are at increased risk. Newborns and young children are also at increased PAES risk due to congenital causes. During embryonic development, the medial head of gastrocnemius migrates medially and superiorly. This migration can cause structural abnormalities, such as irregular positioning of the popliteal artery, and can account for the rare instances of entrapment caused by the popliteus muscle. == Pathophysiology and classification ==

PAES can be classified as either congenital or functional. Analysis of human embryological development has shown that the popliteal artery and the medial head of the gastrocnemius muscle arise at approximately the same time. Because of that, abnormal development of muscle's position in relation to the nearby vessels can result in potential vascular compromise. This system classifies PAES into three main types: • Type 1: The problem lies in the abnormal position of the popliteal artery. • Type 2: The problem lies in the abnormal insertion of the medial head of the gastrocnemius muscle. • Type 3: Both types 1 and 2 are present. ==Medical history and physical examination==

Patients with PAES are typically healthy young males without previous history of cardiovascular risk factors such as smoking, hypertension, hypercholesterolemia, or diabetes. Typically, patients present with posterior intermittent claudication that is worsened with exercise and relieved with rest. Associated symptoms include numbness, discoloration, pallor, and coolness in the affected lower extremity. ==Diagnosis==

Differential diagnosis • Chronic exertional compartment syndrome: Chronic pain and swelling of the affected muscle secondary to increase intramuscular pressure during exercise. • Unresolved muscle strain: An injury or damage to the muscle or its attaching tendons. • Medial tibial stress syndrome: Pain occurs over the shin bone (the tibia) with running or other sport-related activity. • Fibular and tibial stress fracture: Non-displaced microscopic fracture of the fibular and tibia occurs in many athletes, especially runners, and also in non-athletes who suddenly increase their activity level. • Fascial defects: The protrusion of the muscle through the surrounding fascia leads to pain and swelling of the area. • Sciatic nerve entrapment syndrome: The sciatic nerve becomes entrapped by muscles or other structures. • Vascular claudication (secondary to atherosclerosis): The obstruction of arterial flow leads to muscular ischemia and causes pain in the buttock and calf. More common in the elderly with cardiovascular risk factors. • Lumbar disc herniation: A bulging disc or a herniated disc in the lower back which causes radiating pain from the buttock into the leg and sometimes into the foot. Diagnostic challenges PAES is a particularly difficult condition to diagnose, and is easily and frequently missed. Type VI PAES, also known as functional PAES, often is missed as scans of the area lack anatomical abnormalities. Notably, PAES patients are often misdiagnosed with chronic exertional compartment syndrome. Based on a systemic review by Sinha et al, digital subtraction angiography (DSA) is the most common imaging used for PAES diagnosis, followed by ankle–brachial index (18 percent), computed tomography angiography (CTA) (12 percent), magnetic resonance angiography (MRA) (12 percent), duplex ultrasonography (DU) (10 percent), exercise ankle-brachial index (4 percent), and other modalities (4 percent). Provocative maneuvers can be used to improve visualization of PAES on the images. The patient is initially positioned supine with the legs straight, and then instructed to forcefully plantar-flex. A plantarflexion force of 0 to 70 percent maximum has been shown to maximize the sensitivity and specificity for PAES diagnosis. The DU can be a quick, inexpensive, and noninvasive initial screening for PAES. Flow velocities in the popliteal artery will increase, as the popliteal artery is compressed, which is reflected on the DU. If DU is negative but there is still strong suspicion for PAES, MRA or CTA with provocative maneuvers are needed as follow-up imaging. MRA would demonstrate a focal occlusion or narrowing of the mid-popliteal artery, post-stenotic dilatation, or aneurysm of the distal popliteal artery. If MRA or CTA is non-conclusive, DSA may be used as a further option with a high sensitivity (> 97%) for PAES diagnosis. Additionally, functional PAES in which the gastrocnemius hypertrophy causes arterial compression during exercise can be best evaluated with dynamic CT. For dynamic CT, initial images are taken with the patient still. Further images are taken following a series of provocative maneuvers. ==Management==

• Asymptomatic patients: the management is typically expectant. PAES may be found incidentally on the imaging, but the patient may be symptom-free, thus, no intervention is required. The release of entrapment is achieved by performing division of the medial head of the gastrocnemius or musculotendinous band. The surgery can be performed with either posterior or medial approaches. Previous studies show a medial approach is beneficial for type I and II while a posterior approach is better for type III and IV. Additionally, the use of Botulinum Toxin A has been used as an alternative noninvasive treatment for functional PAES. A diagnosis of functional PAES is made if symptoms are improved after Botulinum injection. However, If symptoms are persisted, the patient can undergo an additional Botulinum injection or proceed with surgical decompression. The outcome following the surgery is usually favorable. Successful resolution of PAES occurs in 77 percent of cases. Surgical complications include deep vein thrombosis, hematoma, wound infection, or seroma. After the surgery, patient is usually monitored using arterial duplex ultrasonography 1, 3, 6, and 12 months, and annually after that. ==Complications of untreated PAES==

Early detection and management of PAES can lead to a favorable outcome. Complications of PAES may include: • Distal arterial thromboembolism. • Popliteal artery thrombosis. • Popliteal artery stenosis. • Limbs amputation. Nonetheless, the course of PAES is often slow and takes time, thus, limbs loss is rarely seen, even in PAES patients. ==References==