Pathophysiology

To ensure adequate venous return from the lower limbs, the superficial veins, deep veins, bicuspid valves and the calf muscle must all work together [7]. The deep veins carry blood back up the leg and consist of two posterior tibial veins, two anterior tibial veins and two peroneal veins which join up to form the popliteal vein which in turn continues into the femoral veins. These veins are situated deep in the muscles of the leg and are protected by a fibrous fascia. The large volume of blood carried by these veins results in a high pressure within the vein walls [8] whereas the superficial veins, consisting of the long saphenous veins, short saphenous veins and numerous superficial collaterals, satellites and confluents of the saphenous veins (Figure 1), carry a smaller volume of blood at a lower pressure. The superficial veins drain into the deep veins by means of the perforating veins. Bicuspid valves, present in both superficial veins and deep veins, ensure that the flow of blood is unidirectional and when these valves are competent they prevent a backflow of blood from the deep veins to the superficial veins.

Figure 1 - Long and short saphenous system

The power to drive the blood back up the leg is provided by the calf muscle, which on walking contracts and relaxes in a regular movement. The contraction of the calf muscle forces the blood upward out of a segment of vein; backflow is prevented by the valve [7]. Relaxation of the calf muscle allows the now empty segment of deep vein to refill with blood from the superficial veins and thus the cycle is repeated.

When valves become incompetent the cycle of unidirectional blood flow is interrupted and backflow of blood occurs (Figure 2). This is most significant when the backflow occurs between the deep and superficial veins, as the increased pressure in the superficial veins will cause further valve incompetence. This is because the valve cusps no longer meet as a result of the stretching of the veins. The overall effect of this increased superficial hydrostatic pressure is the formation of tortuous varicose veins [9].

Figure 2 - Venous system (normal and damaged)


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