Continuing Education Activity

The rare clinical manifestation of Popliteal Artery Entrapment Syndrome (PAES) was defined approximately 40 years ago. It has a preference for young to middle-aged patients. The hallmark of this disease is a vascular compromise within the popliteal fossa resulting in an insidious, progressive course of exercise intolerance and calf pain with exertion relieved by rest (claudication). While the incidence of this disease has risen slightly in recent years, the true prevalence is unknown as the number of cases is likely underreported. This activity describes the evaluation, and treatment of PAES, and reviews the role of the interprofessional team in managing patients with this condition.

Objectives:

• Identify the most common age group to be affected by popliteal artery entrapment syndrome.
• Describe the most common clinical presentation of popliteal artery entrapment syndrome.
• Summarize the treatments available for popliteal artery entrapment syndrome.
• Outline the medical management and education options the interprofessional team should provide to a patient with popliteal artery entrapment syndrome.

Introduction

Popliteal artery entrapment syndrome (PAES), described by Stuart in1879, is an uncommon limb-threatening vascular entity comprising approximately 0.17%-3.5% of the general population in the United States (US)[1][2][3]. This embryologically developmental anomaly results mainly due to an aberrant relationship of the popliteal artery with the surrounding popliteal fossa myofascial structures[4][5]. Surprisingly, PAES predominantly effects active young males without a previous history of cardiovascular risk factors[3]. Furthermore, patients with PAES primarily present complaining of intermittent pain in the feet and calves that usually occurs after the exercise and vanishes at rest[3]. Moreover, the advances in radiological imaging likewise allowed far better delineation and also enhanced sensitivity in detecting PAES[6]. A combination of the magnetic resonance imaging (MRI) with arteriography has been reported to be one of the most accurate diagnostic approaches for the PAES[6][7].

Additionally, the management of uncomplicated PAES usually includes the surgical exploration with the addition of fasciotomy, the myotomy, or the release of the popliteal artery by sectioning the fibrous bands[8][5]. Likewise, if left untreated the PAES can lead to the popliteal artery stenosis (PAS), popliteal artery thrombosis (PAT), as well as distal arterial thromboembolism (DAT)[7]. The current article discusses the underlying pathophysiology of the PAES, highlights the relevance of a detailed history and also physical examination to illuminate the diagnosis of  PAES, and also elaborates the necessary information that leads to the identification of high-risk patients requiring urgent surgical intervention.

Etiology

Both congenital and acquired mechanisms have been proposed in the development of PAES[7]. An in-depth understanding of the various stages of human embryological development has successfully demonstrated the precise etiology of the congenital PAES. Developmentally, the popliteal artery and the medial head of the gastrocnemius muscle develop about the same time. Both femoral and sciatic artery contributes significantly to the development of the popliteal artery[7][9]. It originates from the extension of the femoral artery proximally and the sciatic artery distally. Additionally, the sciatic artery contributes to the development of the tibial arteries as well[9][10]. Over time, the sciatic artery regresses, and femoral artery becomes the main contributor to the development of the popliteal artery[9].

The embryological phases of the plantaris muscles play a significant contribution to the congenital PAES[11][4]. The plantaris muscle is related to the superficial group of the posterior crural muscular tissues and has a pivotal function in the plantar flexion of the ankle joint[9]. However, this muscle is almost vestigial and assumed to act in combination with the gastrocnemius. Furthermore, it has been reported to be aberrant in approximately 10% of the cases as well[9]. When this muscle develops aberrantly, it has the potential to trap the popliteal artery leading to the sign and symptoms of the claudication[9].

Furthermore, various anomalies regarding the relative position of the popliteal artery, medial head of the gastrocnemius (MHG) and popliteus muscles define the multiple types of PAES[7]][12]. Also, the aberrant migration of the medial head during embryological development can result in malpositioning of the muscle concerning the nearby vessels[9]. Interestingly, most of the people born with this congenital anomaly mostly remain asymptomatic, suggesting a likely multifactorial process contributing to disease progression[13]. Although this pathology is present from birth, it appears later, likely due to changes related to use of the gastrocnemius muscle in activities such as running or marching causing muscle hypertrophy with external compression and impingement of the popliteal artery by the medial head[14].

Epidemiology

Although PAES remains an essential cause for vascular compromise, over the last few decades, the incidence of this uncommon abnormality has increased[15][16]. In a recent case report published on this unique clinical entity, Wady et al. reported the overall incidence of PAES to be in the range of 0.17% to 3.5% general population[17]. Furthermore, 85% of patients affected with this condition are males, with almost 60% of cases occurring in young athletes during the third decade of life [17][5]. Moreover, in about 30% of the case, the disease has a bilaterally symptomatic presentation[18]. 

Pathophysiology

Generally, the majority of the PAES cases are due to the embryological anomalies while fewer patients have been documented having acquired (fibrous bands) causes for the PAES[7]. Additionally, the PAES are further classified into six different types based on the relationship of the medial head of the gastrocnemius muscle with the popliteal artery[7]. 

• Type I: An aberrant medial course of the popliteal artery around a normally positioned MHG[7]
• Type II: MHG attaches abnormally and more laterally on the femur causing the popliteal artery to pass medially and inferiorly[7]
• Type III: Abnormal fibrous band or accessory muscle arising from the medial or lateral condyle encircling the popliteal artery[7]
• Type IV: Popliteal artery lying in its primitive deep or axial position within the fossa, becoming compromised by the popliteus muscle or fibrous bands[7]
• Type V: The entrapment of both the popliteal artery and vein due to any of the causes mentioned above[7]
• Type VI: The muscular hypertrophy, resulting in a functional compression of both the popliteal artery and vein[7]

The functional PAES (Type VI or F) describes another subtype of the disease that is not due to inherited anatomic abnormalities[19]. It has been postulated that repeated microtrauma results in the growth of connective tissue, destruction of the internal elastic lamina, and damage to the smooth muscles resulting in fibrosis and scar formation[19]. The resulting injury leads to the thrombosis, embolization, and aneurysmal degeneration[19]. 

A more straightforward and practical classification system for the PAES was also introduced by Heidelberg et al.[19]. According to this classification, the PAES is classified into the following three main types[19] 

• Type 1: The problem lies in the course of the popliteal artery[19] 

• Type 2: The muscular insertion is atypical[19]

• Type 3: Both of the abovementioned conditions are present[19]

History and Physical

A high degree of clinical suspicion is warranted as the patients affected with the PAES can face significant physical impairment. Symptoms usually present in the second to third decade of life and are insidious in onset[5]. Classically, the affected patients are younger athletes without a previous history of cardiovascular risk factors[20][7]. Typically, patients present with the complaints of leg and foot claudication that can be quite severe and disabling[7][10][20]. Besides, the patient might likewise notice lower extremity numbness, paresthesia, discoloration, pallor, and coolness.[20][12] Moreover, the physical examinations usually reveal hypertrophy of the calf muscles[20][13][21]. Also, the dorsiflexion/plantar flexion of the foot may elicit diminished, unequal, or even absent pulses[20][22], and as the disease progress, the ankle-brachial index (ABI) will also tilt towards the lower limit[20][23]. Tercan et al. in a study also reported that the absence of the food pulses during the active plantar flexion and passive dorsiflexion of the foot is characteristic for the PAES[24]. 

Evaluation

Diagnosis of the PAES poses a considerable clinical challenge as it calls for the proper interpretation of clinical as well as radiological aspects of this rare clinical entity. Radiologically, to achieve the higher sensitivity in detecting the PAES, a combination of the radiological tests elaborating not only the functional and anatomical status of the popliteal artery; but also the structural details of the popliteal fossa are favored[7][25]. In a recent study on exploring the best diagnostic modality for the PAES, Willimas et al. reported that a combination of the MRI and the duplex ultrasonography (DU) is far superior in diagnosing PAES[25].

Besides, the duplex arterial ultrasonography (DAU) using provocative maneuvers (leg/foot positioned first in a neutral position and then in resisted plantar flexion) provides a quick, inexpensive, and non-invasive initial screening test[26]. Findings of arterial compromise or prominent collaterals in the fossa suggest the diagnosis of PAES[26]. In addition, the angiography can also be performed with provocative maneuvers and would typically demonstrate a medially deviated proximal popliteal artery, focal occlusion or narrowing of the mid-popliteal artery, post-stenotic dilatation or aneurysm of the distal popliteal artery[27]. Testing with computed tomography (CT) angiography or magnetic resonance angiography (MRA) can confirm the diagnosis when the artery is occluded but do not allow for provocative testing[28].

Treatment / Management

The management of the PAES is tailored based on the presence and absence of the symptoms[7]. For asymptomatic patients with incidental findings of popliteal artery entrapment, management is typically expectant, as the majority of these patients never experience symptoms or disease progression[20]. On the contrary, if muscle insertion abnormalities are the cause of the PAEs even in an asymptomatic patient, surgical correction is the preferred method of treatment[7][8].

Furthermore, for symptomatic PAES patients, surgical resection has been the management of choice [29][30]. Surgery with popliteal artery release allows for the definitive reestablishment of normal anatomy and often portends excellent results[29]. Through either a posterior or medial approach, the MHG or musculotendinous band can be divided. The artery can then be palpated to determine its patency and determine if the bypass is required[31]. Reconstruction of the adjacent muscles is not necessary as this is well tolerated without functional limitation[31].

Also, the open surgical procedures offer the best results to address the PAES and assess the artery for repair or bypass[2]. In cases where there is extensive arterial wall damage, occlusion, or aneurysm development interposition bypass grafting, using autogenous vein via a posterior approach or medial bypass to extend farther down the below-knee popliteal artery have been advocated[32]. The medial approach may be better for the management of Type I and II, while a posterior approach may be better for type III and IV[33]. 

Moreover, the management of functional PAES is still controversial although some have had success with gastrocnemius debulking[14]. Also, postoperatively, surveillance is performed using arterial duplex imaging at 1, 3, 6, and 12 months, and annually after that[7]. 

Differential Diagnosis

Various surgical and non-surgical conditions mimic the PAES which add additional challenge in diagnosing this limb-threatening condition. The differential diagnosis for the PAES include but not limited to 

• Chronic exertional compartment syndrome[34]
• Medial tibial stress syndrome[35]
• Fibular stress fractures[36]
• Tibial stress fractures[37]
• Fascial defects[38]
• Nerve entrapment syndrome[39]
• Referred pain from lumbar disc herniation[40]

Prognosis

The prognosis of the PAES entirely relies on its detection time. If PAES is detected and managed early in the course of the disease, the prognosis of the PAES  is generally reasonable[33]. However, if the PAES is detected late when extensive arterial damage has already happened, then the patient is at risk of having permanent claudication or even limb[33]. Nonetheless, the limb loss in patients with PAES is still extremely rare even in the setting of extensive disease because the arterial occlusion is usually slow and takes a lot of time[33]. 

Complications

PAES is a limb-threatening vascular disorder demanding of early clinical diagnosis and early intervention. If this disorder is undetected, PAES can lead to the

• Popliteal artery stenosis (PAS)
• Popliteal artery thrombosis (PAT)
• Distal arterial thromboembolism (DAT)
• Limb amputation 

Deterrence and Patient Education

Following steps should be part of PAES patient education.

• The patient should be educated about the cause of the PAES as detailed as possible. 
• They should be educated that earlier surgical intervention is the only way to reverse the progression of the disease and offers the best treatment. 
• Post-operatively patient must be educated about the signs and symptoms of the compartment syndrome.

Enhancing Healthcare Team Outcomes

PAES is a rare vascular disorder seen in young people. The diagnosis is difficult and thus requires an interprofessional team that includes a radiologist, nurse practitioner, vascular surgeon, primary care provider, and an emergency department physician. The treatment depends on the symptoms. The primary care provider can observe asymptomatic patients, but symptomatic patients require treatment. There are several treatments besides an open vascular bypass. Following treatment most patients have a good outcome; however, several patients may develop nerve injury following surgery (Level V).