The major deep veins of the lower extremities follow the course of the corresponding arteries. The deep venous system of the calf includes the anterior tibial, posterior tibial, and peroneal veins. In the calf, these deep veins present as pairs on both sides of the artery. The posterior tibial vein receives blood from the medial and lateral plantar vein and drains the posterior compartment of the leg and plantar surface of the foot. This vein lies behind the tibia and joins the popliteal vein at the posterior knee. The anterior tibial vein is the upward continuation of the dorsal pedal vein. It runs along the anterior compartment of the leg just above the interosseous membrane between the tibia and the fibula, and joins the posterior tibial vein to form the tibioperoneal trunk and popliteal vein. The peroneal vein runs along the posteromedial aspect of the fibula and joins the posterior tibial vein.

The popliteal vein is formed by the junction of the anterior and posterior tibial veins at the lower aspect of the posterior knee. It ascends along the posterior aspect of the knee and the distal aspect of the anteromedial thigh. The popliteal vein is located medial to the artery in the lower knee, superficial to the artery at the posterior knee, and to the lateral side above the knee.

After the popliteal vein goes into the adductor hiatus, it is referred to as the femoral vein. The term superficial femoral vein is no longer recommended, because this vein is not a superficial vein, but rather a deep vein [9-11]. In the lower part, it lies lateral to the artery; in the mid-part, behind the artery; and in the upper part, medial to the artery. The deep femoral vein from the inner thigh, running along the deep femoral artery, joins the femoral vein and forms the common femoral vein, which is located medial to the common femoral artery. The inguinal ligament is the landmark that divides the common femoral vein from the external iliac vein (Fig. 3).

It is convenient for the US examination to begin with the patient in a supine or semi-Fowler position. The reverse Trendelenburg position, if possible, is also recommended, as it facilitates venous filling in the lower extremities and makes the veins dilate. External rotation of the hip and slight flexion of the knee helps to decrease muscle tension and is good both for exposing the deep veins in the medial thigh, posterior knee, and calf, and for the compression maneuver (Fig. 4A).

Veins drain blood in the distal-to-proximal direction to the right side of the heart. However, it is convenient to examine the deep veins from a proximal to distal direction because the proximal veins are larger in diameter and easy to detect. At the level of the inguinal ligament, in the transverse view, the examiner can see the common femoral vein on the medial side of the artery (Fig. 4B). Information about the flow pattern of the vein can be assessed in the longitudinal view with Doppler US [12]. Following the common femoral vein, it bifurcates into the deep femoral vein and the femoral vein (Fig. 4C). In the more distal part of the medial thigh, only the femoral vein is visible (Fig. 4D).

When the transducer approaches the popliteal fossa of the posterior knee, the popliteal vein is visible. The popliteal vein is superficial to the popliteal artery at the posterior knee (Fig. 4E). Duplicated femoral veins or popliteal veins can be seen [13]. Because a duplicated venous segment may result in false-negative results, both lumens should be carefully examined (Supplementary Fig. 1). Manual vein compression is recommended every 3-4 cm [3].

When tracing the popliteal vein downward, two posteriorly branching veins are found in the calf from the posteromedial approach. The vein along the tibia is the posterior tibial vein, and the vein along the posteromedial aspect of the fibula is the peroneal vein. In a US approach, the cortical shadow of the tibia and fibula can be used as a bony landmark. The paired veins are present on both sides of the artery (Fig. 4F). After stretching the patient’s leg, the anterior tibial vein can be visualized from an anterolateral approach (Fig. 5). Just above the echogenic interosseous membrane between the tibia and the fibula, the anterior tibial artery and vein can be found. If the posterior tibial vein cannot be traced in the proximal to distal direction, it is helpful to trace the vein upward from the posterior to the medial malleolus, where this vein is located more superficially. If the popliteal and calf veins are not visualized well in the supine-based position, the prone or decubitus position can also be helpful. The distal femoral vein at the level of the adductor hiatus can be difficult to evaluate because of its depth and the transducer location.

The two major superficial veins of the lower extremities are the great saphenous vein (GSV) and small saphenous vein (SSV). The terms “greater saphenous vein,” “long saphenous vein,” “lesser saphenous vein,” and “short saphenous vein” are no longer recommended for the purpose of standardizing terminology [10,11].

The GSV begins in the medial marginal vein of the dorsum of the foot, ascends anteriorly to the medial malleolus, and passes posteromedially to the knee. The vein then ascends medially in the thigh to perforate the muscular fascia and join the common femoral vein at the saphenofemoral junction, a few centimeters distal to the inguinal ligament. Tributaries of the GSV are variable between individuals, but there are general rules for naming them [10]. If the course of the tributary is parallel to the GSV, it is called an accessory GSV (an anterior accessory GSV or a posterior accessory GSV). When the tributary courses obliquely, it is called the circumflex vein (the posterior thigh circumflex vein or the anterior calf circumflex vein) (Fig. 6A). However, despite attempts to standardize the terminology, various terms have been used and many of the tributaries are difficult to name.

The SSV arises from the dorsal pedal arch and ascends posterolaterally from behind the lateral malleolus. It ascends along the middle of the calf and ends in the popliteal vein in the posterior knee. However, there are many variations in the termination of the SSV, including without connection to the popliteal vein [5,14]. Before it penetrates the muscular fascia, it may branch out a cranial extension that goes upward to join the GSV through the posterior thigh circumflex vein (the vein of Giacomini) (Fig. 6B).

Insufficiency of the superficial veins should be evaluated with the subject in the erect position, as the supine position may underestimate or miss the reflux of the venous flow (Fig. 7A). The reverse Trendelenburg position can be used if an erect position is impossible. The examined leg should be in a non-weightbearing position [1]. The saphenofemoral junction is visible on the anteromedial surface of the common femoral vein in the transverse view. A longitudinal view of the saphenofemoral junction (Fig. 7B) is useful for assessing reflux of the terminal valve with the help of Doppler US (Supplementary Fig. 2). Normally, the terminal valve at the saphenofemoral junction prevents backward flow into the GSV. After a provocation test, such as the Valsalva maneuver, retrograde flow in the proximal GSV persisting for more than 0.5 seconds is defined as pathologic reflux [4,15].

There is an echogenic fascia surrounding the GSV that is bordered deeply by the muscular fascia and superficially by the saphenous fascia. This saphenous compartment is readily visualized on US and is described as having an “Egyptian eye” appearance (Fig. 7C). The saphenous compartment is also visible at the knee level, above the tibia and medial gastrocnemius (Fig. 7D). Unfortunately, however, there are many variations in the relationship of the fascial compartment to the GSV. Sometimes there is a large tributary outside of the saphenous compartment, while the distal GSV is hypoplastic or even absent [14,16].

The SSV is visible at the middle of the gastrocnemius belly in the fascial trunk (Fig. 8). In tracing the SSV upward, it enters into the popliteal vein. The longitudinal view of the saphenopopliteal junction, like the saphenofemoral junction of the GSV, is useful for assessing insufficiency of the SSV. In the saphenopopliteal junction, calf squeezing augments the venous flow at first, followed by retrograde flow. As described above, however, there are many anatomical variations in this region, and the saphenopopliteal junction may be absent or rudimentary [5,14].

The perforating veins connect the deep veins with the superficial veins and direct the flow from the superficial to the deep system. There are numerous perforators in the leg. According to a consensus statement [10], perforators are named after their locations. Major groups classify perforators according to their longitudinal location as ankle, leg, knee, and thigh perforators. Subgroups indicate side (i.e., anterior, posterior, medial, and lateral perforators). Thus, the complete name of the perforator is a combination of the level and side (i.e., the medial leg perforator or the anterior thigh perforator). More detailed subgroups are present for medial thigh and medial leg perforators. The medial thigh perforators are further classified as the perforating vein of the femoral canal and inguinal perforating vein, and the medial leg perforators are subdivided into the paratibial and posterior tibial perforating veins (Fig. 9). This is convenient becausez it eliminates eponyms such as Hunterian, Dodd, Boyd or Cockett, all of which have been used commonly, but are confusing.

Normally, the perforating veins are not clearly visible on US. However, when there is a flow disturbance in the deep or superficial veins or in the case of perforator insufficiency, the perforating veins can be dilated and are readily visible as a penetrating structure through the muscular fascia (Fig. 10A). In the case of varicose veins caused by perforating vein insufficiency, it is important to localize the refluxing point in order to correct it.

This review describes several clinically relevant perforators around the GSV and their connections. The medial thigh and leg perforators are clinically the most important. The medial leg perforator includes the posterior tibial perforator and the paratibial perforator. The posterior tibial perforator, previously known as the Cockett perforator, connects the posterior accessory GSV with the posterior tibial vein in the distal calf. The paratibial perforator connects the GSV or its tributaries with the posterior tibial vein. The proximal paratibial perforator was previously called the Boyd perforator. In the thigh, the perforating vein of the femoral canal, previously called the Hunterian (proximal thigh) or Dodd (distal thigh) perforator, connects the GSV with the femoral vein or the proximal popliteal vein. Insufficiency of these perforators may cause medial thigh and calf varicosities, even in the absence of saphenofemoral reflux (Fig. 10B).