CONTENTS NEXT PREVIOUS HOME FEEDBACK SEARCH
APPLIED ANATOMY OF THE VEINS OF THE LOWER LIMB
This is not an exhaustive description of all the veins of the lower limb. It is a review of those aspects of the anatomy of these veins which are important in understanding venous return from the lower limb, and its derangements.
Normal venous return, in the erect subject, depends to a large extent on the pumping action produced by the compression of the deep veins of the lower limb by the contracting muscles. These deep veins are therefore closely concerned with venous return from the active limb, and will be considered in some detail.
The most important vessels, in relation to derangements of venous return, are the perforating veins, which connect superficial and deep veins; emphasis will be placed on the sites at which these vessels pierce the deep fascia, and the veins which they connect. Throughout this book, the term 'perforating vein' is applied to a vessel which pierces the deep fascia, connecting deep and superficial veins. 'Communicating' veins are those which connect one superficial vein with another.
Paradoxically, although the superficial veins show the most obvious signs of derangement of venous return when they dilate in the condition generally known as 'varicose veins', they are of secondary importance in understanding and treating the disease. These veins, and in particular the variations at the sapheno-femoral junction, will therefore be described in less detail.
The deep and superficial fascia of the lower limb is concerned with the function of the veins, and plays an important part in the action of the venous pumps. The relevant features will be described.
The veins of the foot
The important veins of the foot are the deep veins of the sole, the superficial veins of the dorsum, and the perforating veins connecting them. The veins of the toes, and the veins draining the superficial tissues of the sole, are of no clinical significance.
The deep veins of the foot are the deep plantar venous arch, and the medial and lateral veins. The deep plantar venous arch runs from the proximal end of the first interosseous space, where it is continuous with the venae comitantes of the dorsalis pedis artery, across the foot to the base of the fifth metatarsal, accompanying the deep plantar arterial arch. It is a large vessel, up to 1 cm. in circumference, and receives the deep metatarsal veins and tributaries from the surrounding muscles. It is continuous at its lateral end with the lateral plantar veins, which run back across the sole accompanying the artery of the same name.
The medial plantar veins run from the medial end of the deep plantar venous arch along the medial edge of the sole to join the lateral plantar veins below the medial malleolus and from the posterior tibial veins. The plantar veins receive numerous tributaries from the surrounding muscles, and from the superficial tissues of the sole. They have frequent valves which allow only proximal flow of blood.
The superficial veins of the dorsum are the dorsal venous arch, the marginal veins, and the anterior vein of the leg. The dorsal venous arch lies over the proximal ends of the metatarsal bones. Its medial limb runs back along the medial side of the dorsum to become continuous with the long saphenous vein in front of the medial malleolus. The lateral limb lies along the lateral side of the dorsum, runs below the lateral malleolus, and becomes continuous with the short saphenous vein. The arch receives the dorsal metatarsal veins, the marginal veins, and tributaries from the superficial tissues of the sole. It is connected with the deep vessels by perforating veins, which are described below.
The anterior vein of the leg arises from the distal part of the dorsal venous arch, and runs back across the dorsum of the foot, and up the anterior aspect of the leg. Irregular vessels connect these superficial veins to form a network on the dorsum of the foot.
The perforating veins of the foot can be divided into two groups (Pegum & Fegan, 1967). These are those which connect the superficial veins with deep veins on the dorsum of the foot (the venae comitantes of the dorsalis pedis artery). Two of these are constant, and connect the ends of the dorsal venous arch with the point at which the venae comitantes of the dorsalis pedis artery become continuous with the anterior tibial veins.
The second group is of those perforating veins which connect the superficial veins with the deep veins of the sole. These are found at both margins of the foot, and in the first interosseous space. There are usually five on the medial border of the foot, of which the most posterior is a large and constant in site. This connects the junction of medial and lateral plantar veins with the medial end of the dorsal venous arch, just in from of the medial malleolus. Approximately 50% of these perforating veins have valves which allow blood to flow only from the deep to the superficial veins.
A wide, constant perforating vein at the proximal end of the first interosseous space connects the dorsal venous arch with the deep plantar venous arch. It accompanies the dorsalis pedis artery and veins into the sole. The vessel does not have a valve.
On the lateral border of the foot there are usually three perforating veins, of which one is constant . It is unvalved, and runs from the lateral plantar veins alongside the tendon of peroneus longus to join the lateral marginal vein.
The significance of the direction of blood flow allowed through the perforating veins of the foot is discussed in the section on the plantar venous pump in Chapter II.
The veins of the leg
The deep veins of the leg are: the venae comitantes of the arteries (anterior and posterior tibial veins and the peroneal veins); the popliteal vein; and the intra-muscular veins. The venae comitantes are closely applied to their respective arteries, with frequent vessels joining the two veins, and many valves allowing only proximal flow of blood.
The anterior tibial veins are the continuation upwards of the venae comitantes of the dorsalis pedis artery. They accompany the anterior tibial artery to the upper border of the interosseous membrane, receiving tributaries from the muscles of the anterior compartment of the leg and several perforating veins.
The posterior tibial veins are formed by the junction of the medial and lateral plantar veins below the medial malleolus. They run upwards beside the posterior tibial artery, between the superficial and deep groups of flexor muscles of the leg. They are joined by the peroneal veins, and then join with the anterior tibial veins at the lower border of popliteus to for the popliteal vein. They receive many tributaries from the surrounding muscles, especially soleus, and many perforating veins.
The peroneal veins arise from the postero-lateral aspect of the calcaneum to run behind the inferior tibio-fibular joint, and upwards along the course of the peroneal artery, between flexor hallucis longus and tibialis posterior. They receive tributaries from the surrounding muscles and perforating veins, and then join the posterior tibial veins 2-3 cm. below the commencement of the popliteal vein. The poplitela vein, formed by the union of anterior and posterior tibial veins at the lower border of popliteus, runs upwards through the popliteal fossa, crossing superficially from the medial to the lateral side of the popliteal artery. It is often re-duplicated, especially below the knee-joint line (Mullarkey, 1965). It receives tributaries from the genicular plexus and from the surrounding soft tissues, including both heads of gastrocnemius, and is usually joined by the short saphenous vein.
The intra-muscular veins of the leg are important, because it is these vessels which make up the calf pump. Gastrocnemius is drained by a pair of venae comitantes from each head, which join the popliteal vein. The soleus muscle contains a variable number of wide, thin-walled veins, generally called sinuses, which run the length of the muscle. In the lower half of the leg, these drain by short vessels into the posterior tibial veins. The upper half of soleus drains into both posterior tibial and peroneal veins. The deep flexor muscles are drained by short vessels which join the posterior tibial and peroneal veins at intervals.
These intra-muscular veins are compressed and emptied when the muscles contract, providing the pumping action so important in venous return from the active limb. The vessels through which they empty into the venae comitantes of the arteries of the leg have valves allowing flow only in this direction.
The superficial veins of the leg are the long (great) saphenous and the short (small) saphenous veins, their tributaries, and the communicating veins connecting them. The long saphenous vein commences in front of the tip of the medial malleolus, as the continuation of the medial limb of the dorsal venous arch of the foot. It runs upwards 2-3 cm. in front of the tip of the medial malleolus, and then inclines posteriorly, crossing the medial surface of the tibia. It runs along the medial aspect of the leg, to pass behind the medial condyle of the tibia into the thigh.
It has two main tributaries in the leg. The anterior vein of the leg, which has been described arising from the distal part of the dorsal venous arch of the foot, runs up the anterior aspect of the leg, 2-3 cm. lateral to the anterior border of the tibia. At a variable level in the upper half of the leg, but usually just below the tibial tuberosity, it crosses the medial surface of the tibia and joins the long saphenous vein.
The posterior arch vein begins behind the medial malleolus, occasionally communicating with the constant most posterior perforating vein on the medial border of the foot. It runs upwards to join the long saphenous vein just below the knee. The short saphenous vein begins behind the lateral malleolus as the continuation of the lateral limb of the dorsal venous arch. It runs upwards along the lateral border of the Achilles tendon and, about half-way up the leg, pierces the deep fascia to run in the groove between the bellies of gastrocnemius. In three-quarters of cases it joins the popliteal vein in the popliteal fossa, usually within 3 cm. above the knee joint line, though the junction may be at any level from 4 cm. below to 7cm. above the joint line (Haeger, 1962). Half of such cases have branches which continue to join the deep veins of the thigh or the long saphenous vein.
In one-quarter of all cases the short saphenous vein does not join the popliteal vein. In two-thirds of these, it joins deep or superficial vessels in the thigh, and in the remaining one-third of cases it joins deep veins below the popliteal fossa (Moosman & Hartwell, 1964).
Dodd (1965) described a 'popliteal area' vein, which drains the superficial tissues over the popliteal fossa and the adjoining parts of the back of the thigh and leg. It pierces the deep fascia in the centre of the fossa or at one of its corners (usually in the centre or at the lateral corner) to join the short saphenous, popliteal or gastrocnemial veins.
There a usually two or three communicating veins which run from the short saphenous vein upwards and medially to join the posterior arch vein, with valves which allow blood to flow only in this direction. A tributary of the short saphenous vein runs up the postero-lateral aspect of the leg, over the line of fusion of the posterior inter-muscular septum with the deep fascia. It joins the short saphenous vein in the upper part of the leg, and often communicates with the antero-lateral tributary of the long saphenous vein, just below the neck of the fibula.
There are usually seven to eleven valves in the short saphenous vein, allowing only proximal flow. The number is independent of sex and age (Kosinski, 1926).
The perforating veins of the leg all have valves which allow blood to flow only from the superficial to the deep veins. They are typically associated, not with the saphenous veins, but with their tributaries, and may conveniently be divided into four groups, according to the deep veins with which they are connected, the distinction between direct perforating veins, which join the venae comitantes of the arteries, and indirect perforating vein, which join intra-muscular veins (Le Dentu. 1867), is unnecessary for the understanding of chronic venous insufficiency and its treatment by compression sclerotherapy.
The anterior tibial group of perforating veins connects the anterior vein of the leg with the anterior tibial veins. There is a variable number, from three to ten. Some pierce the deep fascia at the anterior digitorum longus, and others pass along the anterior inter-muscular septum. Three are constant. The lowest is at the level of the ankle joint, the second is about half-way up the leg and has been called the 'midcrural vein' (Green et al., 1958). The third is at the point at which the anterior vein of the leg curves medially to cross the anterior border of the tibia. For the purpose of recording diagnosis, the inconstant perforating veins in this region can be divided into upper, middle and lower groups, in their respective thirds of the leg.
The posterior tibial perforating veins connect the posterior arch vein with the posterior tibial veins, running in the transverse inter-muscular septum. They can be divided into upper, middle and lower groups. The total number of posterior tibial perforating veins may be as high as sixteen (van Limborgh, 1961), but the usual figure is five or six. In the upper group there are one or two, piercing the deep fascia just behind the medial border of the tibia. The middle group is found in the middle third of the leg, and the veins pierce the deep fascia 1-2 cm. behind the medial border of the tibia. At least one of this group is always present. The lower group is found in the lower third of the leg. There are usually three or four, the lowest of which pierces the deep fascia 2-3 cm. behind the lower border of the medial malleolus. Another pierces the deep fascia 5-6 cm. above this, and there are one or two more above this. The highest vein in this group lies at the junction of the middle and lower thirds of the leg.
On the posterior surface of the leg there is a group of soleus and gastrocnemius muscles. There may be up to fourteen (Sherman, 1949) but there are usually three, the upper, middle and lower, and these typically leave the communicating veins joining the short saphenous to the long saphenous vein, rather than the short saphenous vein itself. They may, however, arise somewhat lateral to the short saphenous vein, and connect either with it or with one of its small tributaries. The peroneal group of perforating veins is found along the line of fusion of the deep fascia with the posterior inter-muscular septum. There are usually three or four, though there may be up to ten (van Limborgh, 1961). Two are constant, one just below the neck of the fibula and the other at the junction of the middle and lower thirds of the leg, called the lateral ankle perforating vein (Dodd & Cockett, 1956). The others are very variable in position, and may be divided into upper, middle and lower groups.
These veins arise from the lateral tributary of the short saphenous vein, which ascends close to the line along which those veins pierce the deep fascia. They run to join the peroneal veins, along the posterior inter-muscular septum.
The veins of the thigh
The main deep veins of the thigh are: part of the popliteal; the femoral vein; and the profunda femoris vein. The popliteal and femoral veins are frequently re-duplicated, forming a main channel running through a plexus (Dodd & Cockett, 1956). The profunda vein communicates with the femoral both below, where it joins the plexus in the adductor canal, and above, the vessels joining usually about 5 cm. below the inguinal ligament. These veins receive tributaries from the surrounding muscles and perforating veins, of which the termination of the long saphenous vein is the largest.
The upper part of the popliteal vein comes to lie on the lateral side of the popliteal artery at the hiatus in adductor magnus, where it becomes the femoral vein. This vessel crosses behind the femoral artery from lateral to medial in its course through the adductor canal and femoral triangle. The femoral vein may have up to six valves, but usually three, the commonest site being just distal to the point of entry of the profunda vein, land the second commonest being at, or just distal to, the inguinal ligament (Basmajian, 1952).
The superficial veins of the thigh are the long saphenous vein and its tributaries. The long saphenous vein enters the thigh behind the medial femoral condyle, and runs up the medial aspect of the thigh. It arches slightly forward to join the femoral vein at the saphenous opening, about 4 cm. below and slightly lateral to the pubic tubercle. Its postero-medial tributary (tibial accessory saphenous vein) runs from the posterior aspect of the thigh, where it frequently communicates with the short saphenous vein, to join the long saphenous vein, usually at the level of the junction of the middle and upper thirds of the thigh, but sometimes higher. The antero-lateral tributary of the long saphenous vein (fibular accessory saphenous vein) begins at the lateral side of the upper leg, where it sometimes communicates with the lateral tributary of the short saphenous vein, or the upper peroneal perforating vein. It runs upwards on the antero-lateral aspect of the knee, and then obliquely across the anterior aspect of the thigh to join the long saphenous vein at any point between the mid-point of the thigh and the saphenous opening. The long saphenous vein is joined in the saphenous opening by three small tributaries, the superficial circumflex iliac, superficial epigastric and superficial external pudendal veins.
The average number of valves in the long saphenous vein is 7.2±2.3, plus a constant valve at the termination of the vein. There is nearly always another valve within 5 cm. below this (Cotton, 1961).
The most constant perforating veins in the thigh connect the long saphenous vein with the femoral vein in (Hunter's) adductor canal, and are therefore called the upper, middle and lower Hunterian perforating veins. The upper one pierces the roof of the adductor canal at its upper end. The middle one, which is constant, passes behind sartorious to join the femoral vein. The lower Hunterian perforating vein pierces the deep fascia just above the medial femoral condyle to join the genicular venous plexus.
There are three other perforating vein in the thigh which appear sufficiently often to deserve mention. Two are connected with the antero-lateral tributary of the long saphenous vein, at points where vertical lines drawn upwards from the margins of the patella cross it. These vessels join the tributaries of the lateral circumflex femoral vein. At the point at which the postero-medial tributary of the long saphenous vein crosses the tendons of semi-membranosus and semi-tendinosus, there is frequently a perforating vein which joins the profunda vein.
All of the perforating veins of the thigh have valves which allow blood to flow only from superficial to deep veins.
The fascia of the lower limb
Both the superficial and the deep fascia appear to be of importance in relation to venous return from the lower limb.
The superficial fascia shows two distinct layers. The superficial layer is of loculated fatty tissue, while the deep layer is a strong membrane of collagen, with some elastic tissue. The deep layer is particularly clearly defined in the foot, where it lies superficial to the dorsal venous arch and its tributaries, but deep to the anterior vein of the leg. This deep layer of superficial fascia extends up the leg and thigh, covering the long and short saphenous veins (Sherman, 1949; Sarjeant, 1964), although Mullarkey (1965) stated that it covers only the thigh and upper third of the leg. Sherman (1949) called it a superficial layer of deep fascia, but this term is unsatisfactory, as it is anatomically quite distinct from the deep fascia, except at the hip flexion crease. Also, the dorsal venous arch and saphenous veins are superficial veins, subjected to totally different conditions and pressure changes from the deep veins (Pegum & Fegan, 1967b; Keane & Fegan, 1967), and play a different, though complementary, function in active venous return from the lower limb. The functional boundary between superficial and deep veins is the deep fascia, and the membranous layer which lies over the main superficial veins should therefore be regarded as part of the superficial fascia.
Sarjeant (1964) and Mullarkey (1965) did not state the upper limit of this layer of fascia, but Sherman's (1949) diagrams show it extending to the saphenous opening. It is homologous with Scarpa's fascia of the anterior abdominal wall, and these two fascial layers may be considered as a single continuous sheet, fused with the deep fascia of the thigh at the skin flexure crease of the hip joint, which is the lower limit of Scarpa's fascia. The structure of the two parts of this fascia is similar, containing a considerable quantity of elastic fibres (Davies & Davies, 1962).
The superficial veins can be divided into two groups, according to their relationship with the deep layer of superficial fascia. Deep to this layer lie the dorsal venous arch and both saphenous veins, and superficial to it lie the tributaries of the saphenous veins. It is of interest that, throughout the limb, the veins which lie beneath the deep layer of superficial fascia show considerably less tendency to become varicose than those which lie superficial to it. The main trunk of the long saphenous vein is often only moderately dilated when its tributaries are grossly varicose (Dodd & Cockett, 1956; Cotton, 1961). In the foot, the anterior vein of the leg is commonly varicose when the dorsal venous arch remains normal.
These finding suggest that a function of the deep layer of superficial fascia is to give tangential support to the main veins of the lower limb. This would appear to be particularly important in the foot, where the dorsal venous arch is subjected to the pressures generated in the deep plantar veins (Pegum & Fegan, 1967).
The deep fascia of the lower limb is the functional boundary between deep and superficial veins. Askar & Abou-el-Ainen (1963) described it as two layers, the superficial forming the crural fascia, which continues upwards to form the roof of the popliteal fossa, and the deep forming a layer over the muscles and continuing over the heads of gastrocnemius to join the femoral condoles. The deeper layer is really epimysium. Since the deep fascia surrounds the muscles of the limb, and is relatively inextensible, contraction of the muscles causes a rise in pressure in the fascial compartments in which they lie. This pressure is exerted on the deep veins, and provides the driving force in the calf muscle pump.
Another action, by which the deep fascia may actively squeeze the leg, rather than passively preventing it from expanding, has been suggested by Askar (1965). The fibres of the deep fascia on the posterior aspect of the leg form a diagonal lattice. Into the upper corners of this lattice are inserted extensions of the tendons of the hamstring muscles, which, when they contract, make the fascial tube longer and narrower. This reduction in diameter will compress the deep veins, aiding in the pumping action of the posterior compartment of the leg.
Conclusions
The descriptions of the deep and superficial veins of the lower limb given in this chapter are brief, because variations in the anatomical arrangement are so common that constant features are few. Similarly, the number of perforating veins described is small. Those mentioned are vessels which occur sufficiently frequently, and which are involved in varicose disease often enough, for knowledge of their usual sites and connections to be useful. As for the others, van Limborgh (1961) lists 214, which shows that perforating veins may be found almost anywhere on the limb. A knowledge of the anatomy is not a short cut to diagnosis - it merely makes the diagnosis more meaningful. Careful examination of the whole limb is essential if all incompetent perforating veins are to be found.
Micro-anatomy of the veins of the lower limb
Capillaries unite to form a tube, about 20 microns in diameter, which consists of endothelium surrounded by a thin layer of collagenous fibres. Vessels with a diameter of about 45 microns have occasional smooth muscle cells between the endothelium and collagen. At a diameter of 200 microns a definite muscular layer becomes evident. At greater diameters elastic fibres can be seen.
The veins of the lower limb are generally classified as medium calibre veins, that is between 2 and 9 mm. internal diameter. The layers of the wall are divided into adventia, media and intima.
Tunica adventia: This is the outermost coat of the vessel, consisting of loose connective tissue and thick longitudinal collagenous fibres.
In the larger vessels of the thigh a considerable network of elastic fibres may be found, together with bundles of longitudinal smooth muscle. This muscle lies close to the junction with the media. In the short saphenous vein these longitudinal fibres stretch from valve to valve.
The nutrition of the vessel wall is supplied by vasa vasorum, which compose an arterio-venous circulation in the wall of the vessel. Capillaries from nearby arterioles carry blood to the tissues of the vein wall, while small venules drain it away. Occasionally these venules drain into the lumen of the vessel itself (Maximov & Bloom, 1958).
Tunica Media: In the course of our investigation it has been found that there are distinct differences between this coat and the intima, demonstrable by the reaction to pathological conditions (Chapter V).
The media consists mainly of smooth muscle running in a circular direction. The muscle bundles are separated by collagenous fibres running in a longitudinal direction. The internal elastic lamina divides this coat from the intima, and serves as a useful landmark in assessing intimal reaction. In the larger veins of the thigh there is sometimes an external elastic lamina which separates the adventia from the media and may be of considerable thickness.
Tunica intima: In the veins of the leg, this coat consists of a thin basement membrane on the internal surface of which are situated irregular polyedral endothelial cells. The basement membrane is composed of a thin connective tissue layer with a few cells and occasional very thin elastic fibres. An exudate called cement substance lies over and between the endothelial cells (McGovern, 1954; Florey et al., 1959). The function of this layer is probably to maintain the integrity of the vessel to fluids and to assist smooth flow of the elements of the blood.
When these vessels are collapsed and empty, the intima assumes a characteristic corrugated appearance. The internal elastic lamina shows a thick wavy line. The muscular media appears relatively dense, and the overall appearance is of a thick walled vessel with a narrow lumen.
Nerve supply of veins
Veins, like arteries, are supplied by the sympathetic nervous system. Neutral fibres envelop adventitial cells and muscle cells of the media. Each muscle fibre appears to be innervated separately. Receptor end-organs contained in veins include arborizing fibres and Paccinian corpuscles (Burch & Murtadha, 1956). Work on the sympathetic nerve supply to veins in the cat has shown that stimulation of the sympathetic pathways causes constriction, and section of them produces dilatation of veins (Donegan, 1921; Franklin, 1937; Landis, 1950). Similar results have been obtained in dogs (Alexander, 1956). Stimulation of the lumber sympathetic trunk causes considerable rise in pressure in the small veins of the leg (Salzman & Leverett, 1956). There is evidence that the pressure in temporarily isolated segments of vein in the human forearm can be raised by such stimuli as apprehension, mental arithmetic, respiratory movements, and the application of ice to the skin (Duggan et al., 1953; Page & Weissler, 1959; Martin & White, 1959). This reaction can be abolished by infiltration of local anaesthetic into perivenous tissue.
Some evidence has been produced which shows that decreases in blood pH are followed by local venous dilation (Vos & Gollwitzer-Meier, 1933).
Valves
Venous valves are bicuspid. Each cusp consists of a thin layer of collagen with endothelial cells covering both of its surfaces, and contains a variable amount of smooth muscle (Edwards & Edwards, 1939); Ludbrook, 1966). A detailed study of the micro-anatomy of the valves has been completed in this department (Fegan & FitzGerald, 1966).
The following micro-anatomical arrangements have been observed:
(a) The vein wall is thicker at the base of the cusp of the valve, and this is produced by an increase in muscle fibres in the media. There is some variation in the amount of thickening of this region in different specimens. The fibres in the base of the valve form two groups: there are small bundles running circumferentially; and there are also longitudinal fibres which in some cases appear to split off from the inner portion of the media and extend into the cusp for a varying distance along its length.
Serial longitudinal sections showed that this muscle extends further into the cusp at its middle than at its edges.
(b) Elastic fibres, similar to those of the internal elastic lamina, extend along the whole length of the cusp. These fibres lie to the central side of the cusp, close to the base of the endothelial cells. Clusters of fine elastic strands are frequently present at the base and root of the valve, and these tend to fuse with the main elastic layer which runs the length of the cusp.
(c) In some specimens examined, a capillary of medium calibre, or a group of very small capillaries, were observed in the base of the cusp.
(d) A constant finding was a reduction in the amount of muscle in the media in the sinus region immediately above the valve root. In some specimens the muscle fibres were absent in this region, and the vein wall consisted only of collagen and elastic fibres.
(e) The cusp is elliptically attachedc to the vein wall. Longitudinal sections showed that the cusp is much longer than the diameter of the lumen of the vein in which it is situated. Therefore, when the valve closes, a considerable portion of the central surface of the upper part of the cusp presses against the similar part of the opposing cusp. However, the lower portion of the cusp, including the root, divides the vessel into proximal and distal chambers. The sinus surface is in the proximal chamber, and the lower central surface is in the distal chamber.
(f) The transverse section demonstrates the relationship of the two cusps to each other when the valve is closed. It also shows specialization of the intima between the lateral attachments of the two cusps. This specialized area, or cushion, on the vein wall fills the gap between the lateral attachments of the cusps.
The function of the valve is to direct the flow of blood in a vein, and to prevent or reduce the transmission of intravenous pressure in a retrograde direction. Considerable pressure is produced in the veins of the leg by contraction of the leg muscles (Keane & Fegan, 1967), and the valves of this region must be capable of withstanding it if they are to fulfil their function. The frail nature of these valves suggests the necessity for supportive mechanisms to enable them to function adequately against such pressures. From the site and alignment of the muscle fibres observed in the valves, it seems likely that their action is as follows:
1. Contraction of the circular bundles in the base of the valve, reducing the diameter of the vein at that point.
2. Contraction of the longitudinal fibres in the root of the cusp, tending to shorten, and thus thicken, this portion of the cusp. This action draws the cusps down towards their roots, and away from each other, but the sphincteric action of the circular bundles in the base compensates for this.
3. The upper free parts of the cusps press against the vein wall at the lateral attachments of the valve, and thus, with the intimal cushions, help to seal this potential leak.
The muscle action is probably initiated by the beginning of retrograde flow, which produce compensatory muscle action, such as that which maintains tone in the vein wall. The specialized arrangement of the muscle fibres suggests that the action of valves in veins is not merely that of passive flaps within the vessel lumen but that they actively regulate the flow. While no direct evidence is yet available, it is probable that the same nervous and humoral effects which influence vascular tone also influence the muscle action in the specialized arrangement of the valve.
References
Alexander, R. S. (1956), Circ. Res. 4, 49.
Askar, O. (1965), Brit. J. Surg. 52, 107
Asker, O. & Abou-el-Ainen, M. (1963), J. Cardiovasc. Surg. 4, 114.
Basmajian, J. V. (1952), Surg. Gynec. Obstet. 95, 537.
Burch, G. E. & Murtada, M. (1956), Amer. Heart J. 51, 807.
Cotton, L. T. (1961). Brit. J. Surg. 48, 589.
Davies, D. V. & Davies, F. (1962), Gray's Anatomy, 33rd Edition. London: Longmans.
Dodd, H. (1965) Brit. J. Surg. 52, 350.
Dodd, H. & Cockett, F. B. (1956), The Pathology and Surgery of the Veins of the Lower Limb. London: Livingstone.
Donegan, J. F. (1921), J. Physiol. 55, 226.
Duggan, J., Love, V. L. & Lyons, R. (1953), Circulation, 7, 869.
Edwards, J. E. & Edwards, A. E. (1940), Amer. Heart J. 19, 338.
Fegan, W. G. & FitzGerald, D. E. (1966), to be published.
Florey, H. W., Poole, J. C. F. & Meek, C. A. (1959). J. Path. Bact. 77, 625.
Franklin, K. J. (1937), A Monograph on Veins. Springfield: Thomas.
Green, N. A., Griffiths, J. D. & Levy, G. A. D. (1958) Brit. Med. J. 1, 1209.
Haeger, K. (1962). J. Cardiovasc. Surg. 3, 420.
Keane, T. F. L. & Fegan, W. G. (1967), to be published.
Kosinski, C. (1926), J. Anat. 60, 131.
Landis, E. M. (1960), Physiol Rev. 30, 1.
Le Dentu, A. (1867), Thèse de Paris No. 276.
Ludbrook, J. (1961), Aspects of Venous Function in the Lower Limbs. Springfield: Thomas.
McGovern, V. J. (1954), J. Path. Bact. 68, 41.
Martin, D. A. & White, K. L. (1959), Circ. Res. 7, 580.
Maximov, A. A. & Bloom, W. (1958), Textbook of Histology, 7th Edition.
Philadelphia: Saunders.
Merritt, F. L. & Weinssler, A. M. (1959), Amer Heart J. 58, 382.
Moosman, D. A. & Hartwell, S. W. (1964), Surg. Gynec. Obstet. 118, 761.
Mullarkey, R. E. & Hickam, J. B. (1955), Circulation, 11, 262.
Pegum, J. M. & Fegan, W. G. (1967a), Cardiovasc. Research, 1, 241.
Pegum, J. M. & Fegan, W. G. (1967b), Cardiovasc. Research, 1, 249.
Salzman, E. W. & Leverett, S. D. (1956), Circ. Res. 4, 540.
Sarjeant, R. (1964), Surg. Clin. N. Amer. 44, 1383.
Sherman, R. S. (1949), Ann. Surg. 130, 218.
Van Limborgh, J. (1961), Folio Angiol. 8, Fasc. 3.
Vos, E. & Golliwitzer-Meier, K. (1933), Pflügers Arch. ges Physiol. 232, 749.