Anatomy and physiology of the veins of the lower limbs

Classical anatomy combines the blood outflow pathways from the lower extremities into two systems: superficial and deep. From the standpoint of vascular surgery, it is appropriate to distinguish a third system - perforating veins.

The superficial venous system of the lower extremities consists of the great saphenous vein (v. saphena magna) and the small saphenous vein (v. saphena parva). Clinicians often deal with another saphenous vein - the lateral, the distinctive feature of which is the presence of numerous connections with deep veins. The lateral superficial vein can flow into the great saphenous vein, but can independently drain into the femoral vein or inferior gluteal vein. The frequency of its observations does not exceed 1%. It can be affected simultaneously with the great and small saphenous veins, but we have also observed an isolated pathological process in its basin.

The great saphenous vein is a continuation of the internal marginal vein of the foot. Anterior to the medial malleolus, the trunk of the great saphenous vein is located immediately under the skin and is clearly visualized and palpated in the vast majority of healthy and sick people in a vertical position. Proximally, the great saphenous vein goes under the superficial fascia and is not visible in healthy people. In patients, due to the expansion of the vessel and the presence of dynamic hypertension, the tone of its walls decreases, the great saphenous vein is more clearly visible and better felt by palpation. However, if the superficial fascia is dense, even the great vein is hidden under it. Then diagnostic errors are possible: the trunk of the great saphenous vein is taken to be its tributary, which is closer to the skin and is better defined.

Along its length, the great saphenous vein receives a significant number of tributaries, which are not equivalent in surgical terms. Among them, it is worth noting the frequently encountered vein that begins in the fossa behind the internal malleolus, runs parallel to the main trunk of the great saphenous vein on the shin and merges with it at different levels. The peculiarity of this vessel lies in its numerous connections with the deep veins through the perforant veins.

There are many variants of tributaries entering the ostial section of the great saphenous vein. Their number varies from 1 to 8. The most constant tributary of the great saphenous vein in this area is the superficial epigastric vein (v. epigastrica superficialis). It enters the great saphenous vein from above and closest to its ostium. Keeping this vein untied during surgery is the most common cause of restoration of pathological discharge from the femoral vein to the saphenous veins of the thigh and relapse of the disease. Of the other tributaries, the external pudendal vein (v. pudenda) and the superficial circumflex ilium superficialis should also be mentioned. The superficial accessory and anterior femoral saphenous veins (v. saphena accessoria, v. femoralis anterior) merge with the trunk of the great saphenous vein 5-10 cm distal to the saphenofemoral anastomosis and are often difficult to reach for ligation in the surgical wound. These veins anastomose with other saphenous veins and support varicose changes in it.

The small saphenous vein is a continuation of the lateral marginal vein of the foot. The anatomical features of this vessel include the location of its middle third intrafascially, and the upper one - subfascially, which makes inspection and palpation of the trunk through the skin inaccessible and complicates the diagnosis of its lesions. The anatomy of the proximal part of the small saphenous vein is of surgical interest. It does not always end in the popliteal fossa. In the works, variants were observed when the mouth of the small saphenous vein was displaced upward and it flowed into the femoral vein, or downward, then it was received by one of the deep veins of the leg. In other cases, the small saphenous vein communicates with one of the sural veins. If the latter fails, discharge may be observed not from the popliteal vein, but from the muscular vein, which must be known before surgery in order to clip this anastomosis. One of the vessels in the area of the saphenopopliteal anastomosis deserves special attention - this vein is a direct continuation of the trunk of the small saphenous vein to the thigh, maintains the same direction of blood flow and is a natural collateral for the outflow of blood from the shin. Due to this, the small saphenous vein can end at any point of the thigh. Ignorance of this before surgery is the reason for the ineffectiveness of the operation. Based on clinical signs, it is possible to make a correct diagnosis in exceptional cases. Phlebography can be of some help. But the main diagnostic role is played by ultrasound angioscanning. It was with its help that the sapheno-sural anastomoses were discovered, and the described branch was named Giacomini.

The deep venous arteries of the lower extremities are represented by paired posterior and anterior tibial and peroneal veins and unpaired popliteal, femoral, external and common iliac and inferior vena cava veins. However, doubling of the popliteal, femoral and even inferior vena cava veins can also be observed. The possibility of such variants should be remembered in order to correctly interpret the results obtained.

The third system is perforating or perforating veins. The number of perforating veins can vary from 53 to 112. From 5 to 10 such vessels, located mainly on the shin, have clinical significance. Perforating veins of the shin normally have valves that allow blood to pass only towards the deep veins. After thrombosis, the valves are destroyed. Incompetent perforating veins are credited with the main role in the pathogenesis of trophic skin disorders.

The perforating veins of the leg are well studied and normally have valves that allow blood to flow only towards the deep veins. According to their location, they are divided into medial, lateral and posterior groups. The medial and lateral groups are direct, i.e. they connect the superficial veins with the posterior tibial and fibular veins, respectively. Unlike these groups, the perforating veins of the posterior group do not flow into the deep venous trunks, but close on the muscular veins. They are called indirect.

I.V. Chervyakov described in detail the localization of the perforating veins of the leg: along the medial surface - 4.9-11 cm and 13-15 cm above the medial malleolus and 10 cm below the knee joint; along the lateral surface - 8-9, 13 and 20-27 cm above the lateral malleolus; along the posterior surface - on the border of the middle and upper thirds (inside the midline).

The location of perforating veins in the thigh is less constant, and they seem to be rarely involved in pathology. The most constant is the vein in the lower third of the inner thigh, named after Dodd, who described it.

A characteristic feature of veins are valves. Parts of the valve form a pocket on the wall of the vein (valvular sinus). It consists of a valve leaflet, valve ridges and part of the wall of the vein. The leaflet has two edges - free and attached to the wall, the place of its attachment is a linear protrusion of the wall of the vein in the lumen of the vessel and is called the valve ridge. According to V.N. Vankov, a valve in a vein can have from one to four pockets.

The number of valves varies in different veins and decreases with age. In the deep veins of the lower extremities, there is the greatest number of valves per unit of vessel length. Moreover, the more distal, the more. The functional purpose of the valves is to provide the only possible direction for blood flow through the vessels. In both superficial and deep veins, blood in healthy people flows only to the heart, through perforating veins - only from the subcutaneous vessels to the subfascial ones.

In connection with the upright posture of man, the determination of venous return factors is a difficult and extremely important question of the physiology of blood circulation in the lower extremities. There is an opinion that if the circulatory system is considered as a rigid U-shaped tube, on both knees of which (on arteries and veins) the force of gravity acts equally, then a small increase in pressure should be enough to return blood to the heart. However, the pushing force of the heart alone is not enough. The following factors come to the rescue: pressure of surrounding muscles; pulse of nearby arteries; compression of veins by fascia; arteriovenous anastomoses; "active diastole" of the heart; respiration.

The listed indicators can be divided into central and peripheral. The former include the influence of the breathing phases on the blood flow in the abdominal section of the inferior vena cava, an important central factor of venous return is the work of the heart.

The rest of the factors listed above are located in the limb and are peripheral. A necessary condition for the return of blood to the heart is venous tone. It determines the preservation and regulation of the capacity of the veins. Venous tone is determined by the neuromuscular apparatus of these vessels.

The next factor is arterio-venous anastomoses, which, according to V.V. Kupriyanov, are not developmental defects of the vascular system or the result of its pathological transformations. Their purpose is to unload the capillary network and maintain the required volume of blood returning to the heart. Arterial blood shunting through arterio-venous anastomoses is called juxtacapillary blood flow. If transcapillary blood flow is the only way to meet the needs of tissue and organ metabolism, then juxtacapillary blood flow is a means of protecting capillaries from stagnation. Under normal conditions, arterio-venous anastomoses open already when a person moves into a vertical position.

All the described peripheral factors taken together create conditions for equilibrium between arterial inflow and venous return in a horizontal state or at rest. This equilibrium changes with the onset of work of the lower limb muscles. Blood inflow to the working muscles increases significantly. But its outflow also increases, since the active factor of venous return is included - the "muscular-venous" pump. According to J. Ludbrook, the "muscular-venous" pump is a system of functional units consisting of myofascial formations, a segment of deep veins associated with the corresponding segment of superficial veins. The "muscular-venous" pump of the lower limbs is a technical pump: there is an internal capacity - deep veins with capillaries strictly oriented to a single direction of blood flow - to the heart; the muscles serve as a motor, since, contracting and relaxing, they change the pressure on the deep veins, due to which their capacity sometimes increases, sometimes decreases.

G. Fegan conditionally divides the "muscular-venous" pump of the lower extremities into four sections: foot pump; calf pump; thigh pump; abdominal pump.

The plantar pump is of great importance. Although the muscles of the foot are relatively small in mass, the outflow of blood here is apparently also facilitated by the effect of the mass of the entire body. The work of the plantar pump increases the efficiency of the shin pump, since it works synchronously with it.

The shin pump has been studied the most. Its capacity consists of the posterior and anterior tibial and peroneal veins. Blood from the arteries enters the capillary bed of the muscles, subcutaneous tissue and skin, from where it is collected by venules. During muscle contraction, due to the suction action of the intramuscular veins, they are filled with blood from the capillaries and venules of the muscles, as well as from the cutaneous veins through indirect perforating veins. At the same time, due to the increase in pressure transmitted by neighboring formations to the deep veins, the latter are freed from blood, which, with functional valves, leaves the tibial veins into the popliteal vein. The distal valves do not allow blood to move in the retrograde direction. During muscle relaxation, the intramuscular veins are compressed by muscle fibers. Blood from them, due to the orientation of the valves, is pushed out into the tibial veins. Indirect perforating veins are closed by valves. From the distal sections of the deep veins, blood is also sucked into the more proximal ones. The valves of the direct perforating veins open, and blood flows from the subcutaneous veins into the deep ones. At present, in the activity of the "muscle-venous" pump, two functions are distinguished - drainage and evacuation.

Pathology of the venous system of the extremities is accompanied by a violation of the evacuation capacity of the "muscular-venous" pump of the lower leg, which is accompanied by a decrease in the evacuation index (the ratio of the average time of transport at rest to the average time under load - a radiometric method for studying the evacuation capacity of the "muscular-venous" pump): muscle work either does not accelerate the outflow of blood at all, or even slows it down. The consequence of this is inadequate venous return, disorders of not only peripheral, but also central hemodynamics. The degree of dysfunction of the "peripheral heart" determines the nature of chronic venous insufficiency, accompanying both varicose and post-thrombotic disease of the lower extremities.

[ 1 ], [ 2 ], [ 3 ]