Functional popliteal artery entrapment syndrome (PAES) is an important and possibly underrecognized cause of exertional leg pain (ELP). As it is poorly understood, it is at risk of misdiagnosis and mismanagement. The features indicative of PAES are outlined, as it can share features with other causes of ELP. Investigating functional PAES is also fraught with potential problems and if it is performed incorrectly, it can result in false negative and false positive findings. A review of the current vascular investigations is provided, highlighting some of the limitations standard tests have in determining functional PAES. Once a clinical suspicion for PAES is satisfied, it is necessary to further distinguish the subcategories of anatomical and functional entrapment and the group of asymptomatic occluders. When definitive entrapment is confirmed, it is important to identify the level of entrapment so that precise intervention can be performed. Treatment strategies for functional PAES are discussed, including the possibility of a new, less invasive intervention of guided Botulinum toxin injection at the level of entrapment as an alternative to vascular surgery.
Functional popliteal artery entrapment syndrome (PAES) is an important and possibly underrecognized cause of exertional leg pain. It shares many features with other causes of exertional leg pain, and more than one condition can be present at once, confusing the clinical picture. An understanding of the typical presenting features of the common causes of exertional leg pain is essential, allowing the clinician to determine those suggestive of PAES and requiring further investigation.
Investigating functional PAES is fraught with potential problems and, if performed incorrectly, can result in false negative and false positive findings. The authors believe that currently accepted vascular investigations such as ankle-brachial indices and Doppler ultrasound performed at rest are not accurate in investigating functional PAES. Rather, a review of the literature would suggest that investigations such as provocative Doppler ultrasound and MRI angiography are performed as soon as possible after reproducing symptoms to “capture” the occlusion while it is occurring.
Once the diagnosis of functional PAES is confirmed, there are a number of treatment strategies available. Until recently, definitive intervention was only available in the form of vascular surgery with variable myotomies and releases. We provide information on a Pilot study suggesting a new less invasive intervention of guided botulinum toxin injection to the level of entrapment, as an alternative to surgical intervention.
PAES shares many clinical features with other causes of exertional leg pain, most of which are thought to be more common [
Differential diagnosis and clinical features of exertional leg pain.
Condition | Incidence | Male/female preponderance | Unilateral/bilateral |
Site of pain | Pain present at rest | Pattern of pain |
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MTSS | 13–42% | Possibly female | Bilateral | Posteromedial tibial border | Yes (on palpation) | Pain with activity can warm up and returns on cessation |
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Stress fracture | Unknown |
Possibly female | Unilateral | Variable depending on site of stress fracture | Yes (on palpation) | Pain with impact activity |
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CECS | 27–33% | Nil | Bilateral | Typically anterior and/or deep posterior compartments | No | Crescendo-decrescendo pattern: pain can last for minutes to hours on cessation |
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PAES |
0.6–3.5% |
Possibly male | Possibly unilateral | Typically superficial posterior compartment | Can be at rest (positional) | Crescendo-decrescendo pattern: pain can last for seconds to minutes on cessation |
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PAES |
Unknown |
Possibly female | Likely bilateral | Typically superficial posterior compartment | Can be at rest (positional) | Crescendo-decrescendo pattern: pain can last for seconds to minutes on cessation |
This condition is thought to represent the most common cause of exertional leg pain [
While stress fractures are not common in the nonexercising population, they are thought to represent 0.7–20% of sports medicine clinic presentations [
CECS is thought to have an incidence between 27 and 33% [
PAES can be further divided into two groups, anatomical and functional. In the case of anatomical PAES, there is a clearly defined anatomical lesion that directly leads to entrapment and subsequent occlusion of the popliteal artery. The second and larger subgroup of anatomically “normal” or functional PAES is particularly poorly understood [
Anatomical and functional PAES most likely present in a similar fashion. Patients with anatomical PAES are thought to be older and more sedentary while functional PAES patients are thought to be younger, more commonly female, and more active [
When examining patients with suspected functional PAES, it is important to diagnose and/or exclude other causes of exertional leg pain. Examination includes palpation and percussion over the lower limb to look for signs of bone stress, be it focal at the site of a stress fracture or along a strip of the distal posteromedial tibial border in the case of MTSS. Some authors suggest that PAES must have a combination of pain with hopping, in conjunction with the development of ischaemic signs like pallor, coldness, and reactive hyperaemia [
A validated clinical provocation test for PAES has not been described in the literature. Some authors describe physical examination as unreliable [
We have developed a simple clinical test that can be performed in the consulting rooms. After assessing for a popliteal fossa bruit and examining peripheral pulses at rest, the patient is required to perform 15–20 single leg eccentric heel drops off the edge of a step, while asking about any developing or worsening leg pain. Immediately after the test is performed, the popliteal fossa is again auscultated for a bruit, and peripheral pulses are examined for any reduction. In our experience, it is worth auscultating for a number of minutes after exertion, as more significant cases (with complete occlusion) may initially have no bruit, or at least delayed onset of a bruit as flow reestablishes.
We believe that if patients do not develop pain or discomfort with this test, or if a bruit and/or pulse reduction is not evident, then it is unlikely that the patient is suffering from PAES. Unfortunately, the development of pain/bruit/pulse reduction does not mean the patient has PAES, as it is possible that they may fall into the asymptomatic occluder group. Provided that the patient has clinical features suggestive of PAES, a positive result warrants further vascular investigation.
Despite PAES being a well-defined condition, no clear-cut consensus regarding the diagnostic work-up of these patients exists [ anatomical PAES, asymptomatic occluder (i.e., exertional leg pain due to another cause, but in whom the artery can incidentally occlude), symptomatic occluder, that is, functional PAES.
The ABI is calculated by dividing the systolic blood pressure at the ankle by that at the arm. Measures below 0.8 suggest at least moderate peripheral vascular disease. Some authors recommend the use of ankle brachial indices in standard work-up for functional PAES [
Some authors will routinely perform compartment pressure studies in addition to vascular studies in the work-up of suspected PAES [
Doppler ultrasound provides a relatively cheap, noninvasive, and accessible procedure to assess flow through the popliteal artery, and it is generally recommended that this be the first line investigation for PAES [
Many authors researching PAES suggest that the most important feature in its diagnosis is the reproduction of symptoms with the help of provocative manoeuvres and verification by duplex ultrasonography [
We perform a resting anatomical study first, with the patient in the supine position. We record waveforms and velocities of the peripheral arteries as well as assess for evidence of intimal thickening or fixed arterial disease. The anatomy of the popliteal fossa is assessed, looking particularly for any popliteal artery or soft tissue structure variations or whether the anterior tibial artery has a high bifurcation.
Hoffman et al. [ prone patient holding a position of provocation (knee extension and plantarflexion) against no load, patient is prone and pushing against approximately 25% of maximal plantarflexion force (Figure dynamic loading by pushing against 50–100% of maximal plantarflexion force (Figure
(a) Patient prone and pushing against a wall (in the direction of the arrow) at 25% maximum plantarflexion force. (b) Patient erect and plantarflexing against full body weight.
Symptomatic patients who occlude in the first 2 categories are presumed to represent more severe cases of functional PAES. If the initial 2 assessments are negative, the patient is assessed in an erect weight-bearing position while cycling through range of motion. This is thought to represent somewhere between 50 and 100% maximal plantarflexion force and may more reliably represent what is occurring functionally during activity. If the erect assessment is negative, the patient may attempt similar exertion that elucidates symptoms in a normal training experience, until they are symptomatic.
At this point, we again assess the patient in an erect position as previously described. We will use cine loops to demonstrate the popliteal artery from resting patency through compression to occlusion and mark the site of compression on skin for MRI correlation. We feel that Doppler ultrasound does not adequately demonstrate the anatomy to rule out anatomical PAES and confirmation of occlusion in a symptomatic patient means the patient may be in either the anatomical or functional PAES groups.
MRI is a valuable noninvasive modality that allows optimal visualization of the popliteal artery as well as the surrounding structures [
MRI angiography can demonstrate the level of occlusion, but limitations include the development of movement artifact with forceful plantarflexion positions and inability to hold such a position for prolonged periods [
After positive ultrasound studies, a fiducial marker is placed on the patient’s skin where the popliteal artery is being occluded to help correlate between the ultrasound and MRI site of occlusion. T1 weighted axial and coronal images are acquired to demonstrate the medial head and lateral heads of gastrocnemius, popliteus, and plantaris muscles and their alignment and associations with the femoral condyles and popliteal arteries and nerves. These images are acquired with the patient at rest.
Following these static images, the patient is instructed to dorsiflex and plantarflex their feet whilst acquiring T2 weighted 2D steady state images axially across the popliteal region. Before the final contrast MRI angiogram is performed, the patient is instructed to alternate a neutral ankle position with maximal plantarflexion force until they stimulate the pain that they usually experience (rather than a single sustained forceful contraction). Once they experience this pain, they keep their ankles in plantarflexion whilst we inject the contrast and perform the angiogram (Figure
MRI angiogram of the popliteal fossa showing complete occlusion of the popliteal artery in the left leg.
Based on our review of the literature, Figure
Assessment and treatment protocols for suspected PAES.
Given the described rapid progression of arterial injury, it is recommended that anatomical PAES patients undergo surgery to remove the site of entrapment [
The pathogenesis and progression of functionalPAES are uncertain, but it may be that these patients develop arterial injury more gradually with onset of more significant symptoms later in life [
However the site and amount of muscle necessary to be removed to prevent further occlusion is not always obvious. It is possible that a large segment of muscle will require excision. The popliteal artery will need exploration and there are increased risks of postoperative complications such as seroma (4.6%) and infection (2%) [
The use of botulinum injections for paralysis of muscles to manage medical conditions is well established. There are several descriptions of the use of botulinum in the treatment of muscle spasticity, particularly in cerebral palsy patients [
The proposed mechanisms of action for intramuscular periarterial botulinum therapy for PAES are paralysis of the muscular slip of muscle responsible for the dynamic arterial occlusion, localised muscle atrophy caused by the botulinum which may increase space for the vessel and would explain the prolonged effect of botulinum on this condition beyond the expected therapeutic effect of the medication, possible arterial smooth muscle relaxation of the popliteal artery resulting in vasodilatation.
Unfortunately, to date, there is no published data on the efficacy of botulinum injection in the management of functional PAES. We have commenced a pilot study using intramuscular periarterial injection of BTX-A to treat functional PAES with promising initial results. We hope to publish the outcomes as our cohort size increases, but at present this remains an unproven intervention.
Functional PAES is a condition that is possibly underrecognized and, if left untreated, can result in progressive arterial damage and the risk of developing lower limb ischaemia. It shares many features with other causes of exertional leg pain (especially chronic exertional compartment syndrome) and may coexist with one or more of these. A suggestive clinical history includes features of pain aggravated by exercise, but also possibly at rest with positions of knee extension and plantarflexion. The pain will typically resolve quickly once provocative manoeuvres are ceased, although an ache may persist for hours. Anatomical and functional PAES cannot be distinguished on clinical features alone, and possibly over half of the “normal” population can demonstrate some arterial occlusion with provocative manoeuvres. For this reason, specialized vascular investigations are indicated, particularly a Doppler ultrasound protocol performed at rest and during provocation and immediately after, which can demonstrate real time arterial occlusion and the level it is occurring at. Once occlusion is demonstrated, MRI can demonstrate the definitive anatomy of the popliteal fossa, whether anatomical PAES exists, and the site and extent of functional entrapment. From here, the best treatment can be provided, with consideration of guided Botox injection for functional PAES as a potential new intervention, or progression to surgical intervention.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors acknowledge Queensland X-ray for their assistance in providing high quality affordable investigations to their subjects.