The syndrome is most commonly identified in male patients, and presents with claudication, following exercise or walking briskly. Popliteal artery entrapment is due to symptomatic compression or occlusion of the popliteal artery by a developmentally abnormal relationship of the popliteal artery to the medial head of the gastrocnemius or less commonly the popliteus muscle. Although the anatomic arrangements predisposing to popliteal artery entrapment are common (3%) only a minority (0.16% prevalence) develop the clinical symptomatology required for diagnosis of the syndrome. The syndrome is more common in athletic young male patients with well-developed calf musculature.
Popliteal artery entrapment may result in chronic leg ischaemia. The popliteal artery may develop stenotic arterial degeneration, complete arterial occlusion, thrombus or even aneurysm formation.
6 types of entrapment of described which require MRI for definitive anatomic characterisation. These include:
Type I: Popliteal artery is aberrant with a medial course around the medial head of the gastrocnemius
Type II: Normal artery location, however, medial head of heterogeneous is more lateral, the artery passing medial and beneath the muscle
Type III: Accessory slip of the medial head gastrocnemius passes around the artery
Type IV: The artery lies deep in the popliteal fossa entrapped by the popliteus musculature or a fibrous band
Type V: Both the popliteal artery and vein are eentrapped (this is of importance during decompression when venous thrombosis may be released)
Type VI: Functional popliteal artery entrapment syndrome
As the anatomical variations are extensive and the regardless of type treatment is surgical, the value of the classification system is contentious. Decompression with musculotendinous transection is advised in all cases, with arterial reconstruction if there is significant degeneration or occlusion of the popliteal artery present. If symptomatic asymmetrically, but bilateraly anatomically similar, the unaffected side should also be operated on. Early treatment results in better long term results.
Ultrasound may be of assistance in diagnosis, particularly when combined with plantar/dorsiflexion/exercise Doppler indices, although arterial narrowing or occlusion is best demonstrated by digital subtraction angiography. Plantar flexion and more commonly dorsiflexion may show narrowing not present on baseline images. Exercise is most sensitive. MRI can demonstrate both the arterial anatomy by MRA as well as the muscular anatomy simultaneously. It should be recalled that on MRI images only fat should surround popliteal artery and vein.
The clinical differential diagnosis for exercise induced lower leg pain, includes chronic exertional compartment syndrome, muscle strains (medial head of gastrocnemius) is medial tibial stress syndrome, fibular and tibial stress fractures and nerve entrapment. Findings of these should also be assessed on MRI.