[Variations and valve structure of the truncal femoro-popliteal system]

Abstract

Study of valves is inseparable from that of the main veins in which they are located. While a modal femoro-popliteal system, satellite to the arterial system, is by far the commonest, major variations are seen in approximately 10% of cases. Each main collecting vein has its specificity, according to its width, the course which it follows and whether or not there is a satellite wide calibre artery. Additional features include the chief affluents which its receives, wavering of its course, the supple or rigid perivascular environment and the proximity of large muscle masses. All these features play a role in the quality of drainage, in particular during exercise, and in anti-reflux function. In practice, variations come down to two broad possibilities: the single collector, sometimes made up of several different embryological segments, resulting in a hybrid vessel and an aberrant course, either axial, satellite to the sciatic nerve, or profunda femoris, satellite to the shaft of the femur. Doubling (bifid or by bifurcation) opens up an additional channel, either parallel or divergent, which considerably modifies the conditions of venous return. A lesion affecting one branch only, e.g. a solitary thrombus, may have no clinical manifestations and marking if collectors during imaging. The topography of the valves of the main veins tends to be fairly fixed. They are preferentially located proximal to the main confluents, to winding parts of the course of the vessel, or at certain hemodynamic levels which vary little from one individual to another. An attempt is made at nomenclature, classification and topography. The chief feature, the terminal valve of the lower limb, is located most often at the femoral ring. It alone is capable of opposing the long cavo-iliac reflux caused by effort. Analysis of retrograde phlebography films with caval occlusion shows that reflux is not directly exerted on the valve. The point of interruption is high, in the terminal portion of the external iliac vein. This hemodynamic barrage is purely functional. When there is incontinence of the terminal valve varying degrees of reflux diffusely affect the femoral axis. At the same time, there is regurgitation of contrast medium into the visceral areas of the true pelvis, normally sealed off. This coupling between anti-reflux function of the lim and that of the pelvis is one of the unexpected aspects of valve activity.