PVES is a rare cause of exercise-induced leg pain. Active young people and athletes without risk factors, such as smoking, heart disease, or systemic atherosclerosis, are affected. The symptoms are correlated with the degree of compression of the popliteal vessels. Popliteal vascular structure is normal in the early stage and the disease becomes evident only after vascular compression between the contracting gastrocnemius muscles occurs . Repeated extrinsic vascular compression causes trauma to the vascular wall, leading to premature intrinsic atherosclerosis and thrombus formation. The pathology of PVES is considered to be progressive and resulting stenosis and turbulence can lead to post-stenotic aneurysm. In addition, acute ischemia can occur if there is an occluded artery or aneurysm with thrombosis [2, 9]. Early diagnosis is crucial as PVES is a progressive disorder and early intervention is recommend to prevent serious complications [8, 9].
Color Doppler ultrasound has been widely used to diagnose peripheral vascular diseases [10–13]. This non-invasive examination does not require contrast enhancement, patient preparation before study, or radiation exposure. The present study suggests that ultrasonography is able to show when popliteal artery and popliteal vein are separated, when normal forward and backward alignment of popliteal artery and vein becomes aligned in left and right directions, and medial head of gastrocnemius muscle or abnormal muscle bundle between the blood vessels, which are crucial signs for the diagnosis of PVES. The present study found that the popliteal artery and popliteal vein were separated in 83% (25/30) of the cases, which was consistent with surgical results, suggesting a high ultrasound sensitivity. This included six patients with bilateral popliteal vessel involvement. Collins et al.  reviewed about 22–67% of the bilateral cases. Duplex scanning examination associated with pulsed Doppler offers a more precise scope of the popliteal fossa. This modality makes it possible to identify PVES by showing a popliteal artery may take abnormal course or an anatomical aberrant composition between the popliteal artery and vein that increases the distance separating the two vessels . Separation of the arteries and veins can be shown on the ultrasound because the popliteal artery and popliteal vein move in a left-right direction, even if there is an arterial occlusion. Popliteal vascular ultrasonography on the affected side shows varied degrees of vascular structure pathology, including thickening, lumen stenosis, and occlusion. When the popliteal artery is complicated by aneurysm, ultrasound examination can clearly find local thickening and aneurysmal dilation of the artery lumen. Even if the aneurysm is full of thrombosis, the aneurysm diagnosis can be confirmed. Duplex ultrasound therefore only shows the morphological structure of popliteal vessels, but also provides hemodynamic information . It is a non-invasive method that might prove to be of great value in the diagnosis of PVES.
Provocative maneuvers can provide important information for early diagnosis of PVES. This type of examination allows real-time, dynamic observation of changes in popliteal vessel blood flow before and after the experiment, as well as demonstrates that compression was not detected in the neutral position [4, 17]. The presence of entrapment should be highly suspected when the popliteal artery or vein are compressed. The popliteal vessels usually show signs of narrowing or lumen occlusion and have positive peak systolic velocity results. Therefore, close attention must be paid to the examination of plantar flexion. Three examined cases had no abnormality in the neutral position, but popliteal vessels appeared to be narrowed or occluded during the provocative maneuvers, which was helpful for clinicians to consider the possibility of PVES. It is worth noting that for patients with complete popliteal artery occlusion, there is no blood flow signal in the popliteal artery during color Doppler examination. Thus, provocative maneuver test is applicable to patients without popliteal artery occlusion.
However, in two cases no popliteal fossa malformations were detected by ultrasound and the imaging was not specific. In this group, there were two cases with lower extremity atherosclerosis, with one 58-year-old male with history of left lower limb paresthesia for three years and claudication for four months. Ultrasound imaging found left lower limb artery atherosclerotic plaques and popliteal artery thrombosis. This patient underwent computed tomographic angiography, which showed that the left popliteal artery was entrapped by the medial head of the gastrocnemius which rose more laterally than the normal. Another case included a 55-year-old male who complained about symptoms of lower limb ischemia, such as swelling of the right leg and cold right foot for six months. Ultrasound suggested atherosclerosis of right lower extremities. The popliteal artery and tibiofibular stem Doppler blood flow velocity was decreased. The operation demonstrated compression of the right popliteal artery with a fibrous band that attached to the intercondylar notch after crossing the popliteal artery. Ultrasound examination in the above two patients only diagnosed lower limb atherosclerosis and failed to find popliteal vascular depression. Thus, even though ultrasound scanning can show arterial lesions in older patients affected by atherosclerosis, pathological and etiological analysis still needs to combine clinical data and other imaging examinations.
Currently, it is believed that patients with PVES should undergo a surgical treatment as soon as they are diagnosed. The principle of surgery is that [18, 19] when the popliteal artery is not injured, the medial head of the gastrocnemius muscle causing popliteal artery constriction or abnormal accessory muscle bundles and tendons can be released. In case of popliteal artery injury, endarterectomy and venous patch repair can be used. When popliteal artery is completely occluded, great saphenous vein autograft or artificial vascular bypass can be performed . Doppler ultrasound can reveal locations of the saphenous vein and provide accurate positioning for surgery (Figs. 3d and 3e). In addition, patients with popliteal artery and saphenous vein patency during postoperative follow-up can be evaluated using ultrasonography . For some patients with popliteal artery compression and proximal side aneurysmal dilatation, ultrasound images can indicate the scope of aneurysms and mark them on the body surface, facilitating clinical selection of surgical methods.
Yang et al. suggested that Doppler ultrasound is a simple, rapid, non-invasive procedure that should be used routinely in the evaluation of individuals with suspected PVES . However, the use of Doppler sonography is limited by its small window, operator proficiency, probe pressure, and lack of classification accuracy. Therefore, further imaging studies are required for patients with suspicion of entrapment, even if Doppler results are normal.
The major limitations of our study were the relatively smaller sample of patients and the lack of control group. The results would be more accurate for a larger sample size, but these specific ultrasound findings provide direct evidence, we can still recommend ultrasound as a primary screening examination modality in PVES. In the absence of a healthy control group, the application value of provocative maneuvers in PVES may not be adequately evaluated. In future study, we will continue to collect more case and control study, and further in-depth discussion and improvement.