Anatomy and physiology of the veins of the lower extremities

Classical anatomy combines ways of outflow of blood from the lower extremities into two systems: superficial and deep. From the position of vascular surgery it is expedient to single out the third system - perforating veins.

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

A large subcutaneous vein is a continuation of the inner marginal vein of the foot. Ahead of the medial malleolus, the trunk of the large saphenous vein is located immediately under the skin and in the vast majority of healthy and sick people in a vertical position it is well visualized and palpated. The proximal large subcutaneous vein goes under the superficial fascia and is not visible in healthy people. In patients with the expansion of the vessel and with the presence of dynamic hypertension, the tonus of its walls decreases, the large subcutaneous vein is more clearly visible and palpable. However, if the superficial fascia is dense, then even a large vein disappears beneath it. Then, diagnostic errors are possible: the trunk of the large saphenous vein receives its inflow, which is closer to the skin and is better defined.

In its course, the large saphenous vein takes a significant number of inflows, which are not equivalent in the surgical plan. Among them, one should note a frequently occurring vein, starting in the fossa behind the inner ankle, parallel to the main trunk of the large saphenous vein on the shin and merging with it at different levels. The peculiarity of this vessel lies in its numerous connections with deep veins along the perforated veins.

There are a large number of variants of the inflow of tributaries into the mouth of the large saphenous vein. Their number varies from 1 to 8. The most constant inflow of the large saphenous vein in this zone is the superficial epigastric vein (v. Epigastrica superficialis). It flows into the large subcutaneous vein from above and closest to its mouth. Preservation of this vein unconnected, during surgery, is the most frequent cause of restoration of pathological discharge from the femoral vein to the subcutaneous veins of the thigh and relapse of the disease. Of the remaining tributaries, mention should also be made of the outer vaginal vein (v. Pudenda) and the superficial surrounding iliac bone (v. Circumflexa ilium superficialis). The superficial additional and anterior femoral saphenous veins (v. Saphena accessoria, v. Femoralis anterior) merge with the trunk of the large saphenous vein 5-10 cm distal to the saphenous-femoral anastomosis and are often difficult to achieve for dressing in the operating wound. These veins anastomose with other subcutaneous 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 intrasfascially, and the upper one - subfascially, which makes inaccessible examination of the palpation of the trunk through the skin and makes it difficult to diagnose its lesions. Surgical interest is the anatomy of the proximal small subcutaneous vein. It does not always end in the popliteal fossa. In the works observed variants, when the mouth of a small saphenous vein was displaced upward and it flowed into the femoral vein, or down, then it was taken by one of the deep veins of the shin. In other cases, a small saphenous vein has a message with one of the veins. If the latter is insolvent, there may be a discharge not from the popliteal but from the muscular vein, which it is necessary to know before the operation to clinch this anastomosis. One of the vessels in the zone of the sapheno-popliteal anastomosis deserves special attention - this vein is a direct continuation of the trunk of the small saphenous vein on the thigh, preserves the same direction of the blood flow and is a natural collateral for the outflow of blood from the shin. Due to this, a small saphenous vein can terminate at any point of the thigh. Ignorance of this before surgery causes an inefficient operation. On clinical grounds, it is possible to correctly diagnose in exceptional cases. Some help can be provided by phlebography. But the main diagnostic role is played by ultrasonic angioscanning. It was with his help that the sapheno-sulphide anastomoses were discovered, and the described branch was named Giacomini.

Deep venous lines 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. However, you can observe and doubling popliteal, femoral and even lower hollow veins. The possibility of such options should be remembered in order to correctly interpret the results.

The third system is perforating or perforating veins. The number of perforating veins can range from 53 to 112. Clinical significance is from 5 to 10 such vessels, located mainly on the shin. Perforating veins of the lower leg normally have valves that allow blood only to the side of the deep veins. After thrombosis, the valves are destroyed. Insoluble perforating veins are attributed to a major role in the pathogenesis of trophic skin disorders.

Perforating veins of the tibia have been well studied, valves with blood flow only to the side of the deep veins are normal. By localization, they are divided into the medial, lateral and posterior groups. Medial and lateral groups are straight, that is, they report superficial veins with posterior pubes and peroneal respectively. Unlike these groups, the perforating veins of the posterior group do not flow into the deep venous lines, but close on the muscular veins. They are called indirect.

I.V. Chervyakov described in detail the location of the perforating corneal veins: on the medial surface - by 4.9-11 cm and 13-15 cm above the medial malleolus and 10 cm below the knee joint; on the lateral surface - 8-9, 13 and 20-27 cm above the lateral malleolus; on the back surface - on the border of the middle and upper thirds (inside from the middle line).

The presence of perforating veins on the thigh is less constant, and they, apparently, rarely participate in pathology. The most constant is the vein in the lower third of the inner surface of the thigh, called by the name of Dodd who described it.

A characteristic feature of the veins are the valves. The valve parts form a pocket on the vein wall (valve sine). It consists of a valve flap, valve rollers and a part of the vein wall. The leaf has two edges - free and attached to the wall, the place of its attachment is a linear protrusion of the vein wall in the lumen of the vessel and is called the valve roller. According to V.N. Vankova, 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, the greatest number of valves per unit length of the vessel. And the more distal, the more. The functional purpose of valves is to give the only possible direction for the movement of blood through the vessels. In both superficial and deep veins, the blood of healthy people flows only to the heart, through the perforating veins - only from the subcutaneous vessels to the subfascial ones.

In connection with the uprightness of the person, the determination of the factors of venous return is a difficult and extremely important issue in the physiology of the circulation in the lower extremities. There is an opinion that if the circulatory system is regarded as a rigid U-shaped tube, on both knees (on the arteries and on the veins) the force of gravity affects the same, then a small increase in pressure should be enough to return the blood to the heart. However, one pushing force of the heart is not enough. To help come the following factors: the pressure of the surrounding muscles; pulse of the nearest arteries; compression of veins fasciae; arterio-venous anastomoses; "Active diastole" of the heart; breath.

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

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

The next factor is arteriolovenous anastomoses, which, according to V.V. Kupriyanov, are not the vices of the development of the vascular system or the result of its pathological changes. Their purpose is to unload the capillary network and maintain the necessary volume of blood returning to the heart. Shunting of arterial blood through arteriolovenous 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, arteriolovenous anastomoses open already when the person moves to a vertical position.

All described peripheral factors, combined, create conditions for the balance between the arterial influx and venous return in a horizontal state or in a calm state. This equilibrium changes with the beginning of the work of the muscles of the lower extremities. To the working muscles, the flow of blood greatly increases. But the outflow of it also increases, since the active factor of venous return is activated - 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 container - deep veins with capillaries strictly oriented to the single direction of blood flow to the heart; muscles serve as a motor, because, contracting and relaxing, change the pressure on deep veins, so that their capacity then increases, then decreases.

G. Fegan conditionally subdivides the "muscular-venous" pump of the lower extremities into four sections: a stop pump; pump of the lower leg; pomp of thigh; abdominal pump.

Plantar pump is very important. Although the muscles of the foot are relatively small in mass, the outflow of blood is apparently facilitated by the influence of the mass of the whole body. The work of the plantar pump increases the efficiency of the shin pump, since it works in sync with it.

The most studied pump of the lower leg. Its capacity consists of the posterior and anterior tibial and peroneal veins. Blood from the arteries enters the capillary bed of muscles, subcutaneous tissue and skin, from where it is collected by venules. During muscular contraction, due to the sucking action of the intramuscular veins, they are filled with blood from the capillaries and venules of the muscles, and also through the indirect perforating veins from the cutaneous veins. At the same time, due to the increase in pressure transmitted by the neighboring formations to the deep veins, the latter are released from the blood, which, with the effective valves, leaves the tibia veins in the popliteal vein. The distal valves do not allow blood to move in the retrograde direction. In the period of muscle relaxation, intramuscular veins are squeezed by muscle fibers. The blood from them due to the orientation of the valves is pushed into the tibial veins. Indirect perforating veins are closed by valves. From the distal parts of the deep veins, blood is also absorbed into the more proximal ones. The valves of the straight perforating veins are opened, and the blood from the subcutaneous veins flows into the deep ones. At present, in the activity of the "muscular-venous" pump, two functions are distinguished: drainage and evacuation.

The pathology of the venous system of extremities is accompanied by a violation of the evacuation capacity of the "muscular-venous" shin pump, which is accompanied by a decrease in the evacuation index (the ratio of the mean time of transport at rest to the average time in the load-the radiometric method for studying the evacuation capacity of the "muscular-venous" pump): does not accelerate the outflow of blood, or even slows it down. The consequence of this is an inferior venous return, a violation not only of peripheral, but also of central hemodynamics. The degree of dysfunction of the "peripheral heart" determines the nature of chronic venous insufficiency, which accompanies both varicose and postthrombotic diseases of the lower limbs.

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