J. Anat. (1974), 118, 2, pp. 241-251 241 With 4 figures Printed in Great Britain The and lacunar ligaments

W. J. LYTLE Royal Infirmary, Sheffield (Accepted 12 May 1974)

INTRODUCTION The inguinal and lacunar ligaments have, over the years, been beset by many problems, not only from changes in their names, but also from doubts about their precise anatomy. Gimbernat (1795), in the English translation'of his book on femoral , described in detail the crural arch, subsequently known as Poupart's ligament, and now the . He described the crural arch as a remarkable plait or duplicature backwards of the of the external oblique muscle, more manifest towards the os , having a broad insertion for 1 inch or more into the 'crest' of the pubis. Gimbernat's 'crest' became later known as the iliopectineal line and is now called the pecten pubis. The inguinal ligament is often described as a cord which extends from the anterior superior iliac spine to the , the remainder being named its pectineal part, but as this name is also given to the it will not be used again in this article. The aponeurotic inguinal ligament, as here described, has a 2 5 cm broad attachment to the pubic tubercle and pecten pubis. The lacunar ligament, with its characteristic curved edge, lies much deeper, and is so closely hidden behind the inguinal ligament and posterior inguinal wall that its exact position and relations still remain uncertain. Gimbernat described this deep part as a membranous expansion from the posterior border of the medial part of the inguinal ligament, passing back to the pecten pubis-and inserting itself behind the . This is, in fact, thefascial lacunar ligament derived, as will be shown, from the of the thigh, but it is remarkable that Gimbernat did not mention its important curved edge. However, two curved edges are seen by the surgeon operating on cases of strangu- lated where gangrenous bowel requires resection by a combined approach through the and below the inguinal ligament. The upper curved edge, viewed from within the abdominal cavity, lies on the medial side of the , where it is attached to the pecten pubis. The lower curved edge, seen from below the inguinal ligament, lies on the medial side of the neck of the femoral hernial sac well below the pecten. A full exposure and photograph of the lacunar liga- ment should disclose which of the curved edges belongs to it. Unfortunately, there is much difficulty in exposing thelacunar ligament in the dissecting room, for in hardened preserved bodies the fascial layers of the adhere firmly and resist separation. In the living body, at operations, the lacunar ligament can be exposed and clearly seen, but it lies in a very confined space and is difficult to photograph. I 242 W. J. LYTLE

Fig. 1. Photograph of a dissection of the right groin. Note: 1. Upper and lateral quadrant: cut edge of external oblique aponeurosis. 2. Upper and medial: retractor raises the posterior inguinal wall to show the pecten pubis and lacunar ligament. 3. Lower and medial: inguinal ligament cut and drawn forwards to show the fascia lata laterally and lacunar ligament medially arising from its posterior border. 4. In the centre: large oblong area of of the posterior inguinal wall and femoral sheath with white shining patches on its surface. have illustrated the lacunar ligament by drawings (1957), as have also Madden et al. (1971), but drawings of this elusive ligament have differed so widely over the years that the situation is highly confused. In the fresh cadaver, fascial layers are readily separated, and, by wide incisions and forcible retraction, both inguinal and lacunar ligaments can be clearly displayed and photographed.

OBSERVATIONS Figure 1 is a photograph of a dissection of the right groin, in a male subject, shortly after death. The aponeurosis of the external oblique muscle has been widely divided, 2 cm above and parallel with the inguinal ligament. In the upper and lateral quadrant of the photograph, the upper cut edge of the external oblique aponeurosis is clearly The inguinal and lacunar ligaments 243 seen, but medially, where the three-pronged retractor lies, the cut edge is overlain by fat. This three-pronged retractor has also drawn up, and holds in its grasp the greyish white transversalis fascia of the medial part of the posterior inguinal wall, and this has exposed a 3 cm length of the pecten pubis which lies 1 cm below the prongs of the retractor. Anterior to the pecten is a striking view of the dark grey lacunar ligament with its curved edge. In the medial and lower quadrant of the photograph the white shining fibres of the medial half of the inguinal ligament stand out. The ligament has been cut across 7 cm lateral to the pubic tubercle, whose position is shown by a white circular marker. The cut end of the medial half of the ligament has been seized by partially hidden artery forceps and vigorously pulled downwards and forwards, exposing in the centre of the photograph a large quadrilateral light grey area with shining white patches on its surface. The upper third of this area is the transversalis fascia of the posterior inguinal wall, from which the inguinal ligament has been forcibly detached. The lower two-thirds is the transversalis fascia of the anterior wall of the femoral sheath. Traction on the inguinal ligament has detached its posterior border from the posterior inguinal wall and arising from this border, in front of the femoral sheath, is a dark grey band of fascia. This band when followed medially joins the lacunar ligament. This is the fascia lata of the thigh which is passing down to cover the femoral sheath, and more medially to form the lacunar ligament whose curved edge has also been detached by traction from the femoral sheath. The inguinal ligament The inguinal ligament extends from the anterior superior iliac spine, where it is pointed and narrow, to its broad insertion into the pubic tubercle and along the pecten pubis for 1 5-2-5 cm. The ligament is the lower border of the external oblique aponeurosis folded back at right-angles upon itself. It has an anterior and a posterior border which lie in the same horizontal plane. The ligament is set obliquely in the groin, at an angle which varies from 35 to 40 degrees to the horizontal, and measures some 12-14 cm in length. The fibres of the external oblique aponeurosis do not lie parallel with the inguinal ligament, as is often shown, for each fibre approaches it at an angle which varies from 10 to 20 degrees, and this is well illustrated by Astley Cooper's artist (1844) whose lithograph is reproduced in Figure 2. There is not a simple folding back of the aponeurosis which would result in a ligament of similar strength, with fibres lying obliquely in the ligament and ending at its posterior border. Instead, each oblique fibre of the aponeurosis, on entering the ligament, turns medially to lie in its long axis. Except for some fibres which, near the anterior superior iliac spine, may end in the fascia lata, the fibres all pass to their insertion into the pubic tubercle and pecten pubis. The obliquity of the fibres entering the inguinal ligament allows of a broad band of aponeurosis to be closely packed into a relatively narrow and strong ligament. This broad band can be outlined by splitting the aponeurosis from the superficial inguinal ring, upwards and laterally, along the line of its fibres (Fig. 3). Measuring upwards from the anterior superior iliac spine at right angles to the fibres, the band of the external oblique aponeurosis varies from 3 to 5 cm in width and this band is concentrated into a ligament of less than half its width. Figure 3 shows how the fibres of the broad band of aponeurosis, here shown widely spaced, converge I6 AANA ii8 244 W. J. LYTLE

Fig. 2. Astley Cooper's drawing showing the obliquity of the fibres of the external oblique aponeurosis entering the inguinal ligament. to form a ligament with fibres closely placed in its long axis. In addition, the apo- neurosis is shown turned down to reveal its deep surface, and here the fibres are drawn in interrupted lines to demonstrate their entry into the inguinal ligament. The external oblique aponeurosis is thickest and strongest in the lower and this gives added strength to the ligament. The ligament, of uniform thickness, is pointed and narrow at the anterior superior iliac spine and gradually widens medially as it receives additional fibres from the external oblique aponeurosis, to measure trans- versely from 05 to 1 cm in front of the femoral sheath and from 1 to 1 5 cm near its insertion. Rarely do the fibres of the aponeurosis lie almost parallel with the inguinal ligament and in these cases the ligament is both narrow and weak. The inguinal and lacunar ligaments 245

Fig. 3. Diagram to show how the oblique fibres of the external oblique aponeurosis, shown widely spaced, influence the shape, direction of the fibres and strength of the inguinal ligament. The aponeurosis is turned down, exposing its deep surface, to indicate how its fibres, shown in interrupted lines, are concentrated in the inguinal ligament.

The narrow lateral half of the inguinal ligament, measuring from 6 to 7 cm in length, has an inferior surface fixed to the fascia lata of the thigh, which here appears to be the fascia iliaca continued forward from the posterior abdominal wall. The superior surface is free, and here the fascia iliaca posterior to the inguinal ligament gives attachment to the muscle fibres of the internal oblique and transversus muscles. In its medial half, the ligament broadens to form the floor of the , and the attachments of this broad half of the ligament are complex. The inguinal ligament in Figure 1 has been separated by traction from the transversalis fascia of the posterior inguinal wall, revealing a narrow dark grey band of fascia arising from the posterior border of the ligament. This band at once disappears downwards in front of a strip of black shadow. This band is the fascia lata of the thigh, which is passing down to cover and blend with the anterior wall of the femoral sheath. It is often stated that the fascia lata is attached to the lower border of the inguinal ligament, but a lower border does not in fact exist, for the inguinal ligament lies at right angles to the aponeurosis of the external oblique muscle and has an anterior and a posterior border. It might be assumed that the fascia lata, in early fetal life, was attached to the lower border of the aponeurosis of the external oblique muscle, and when the backward turn of the aponeurosis took place later in fetal life to form the floor of the developing inguinal canal, the fascia lata was dragged back with it and found itself attached to the posterior border of the inguinal ligament. A layer of fascia, which may be the fascia of Scarpa, or derived from it, descends from the anterior I6-2 246 W. J. LYTLE abdominal wall, over the inguinal ligament, to cover and blend with the fascia lata over the femoral sheath; this gives the impression that the fascia lata is attached to the anterior border of the inguinal ligament. Medial to the femoral sheath, the fascia lata, attached to the posterior border of the inguinal ligament, is seen to change direction backwards, on its way to the pecten pubis to form the lacunar ligament (Fig. 1). The transversalis fascia of the most medial part of the posterior inguinal wall has been forcibly retracted upwards by the three-pronged retractor, but normally it passes down to the posterior border of the inguinal ligament and, being blocked here by the lacunar ligament, turns back on its upper surface to the pecten pubis, to form the . This backward turn, drawn upwards by the three-pronged retractor, gives a striking view of the lacunar ligament. The under surface of the inguinal ligament, before it reaches its attachment to the pubic tubercle and pecten pubis, is fixed to the fascia over an area of about 1 cm in width. Between this attachment and the femoral sheath, the under surface of the ligament is free and overhangs a hollow about 1 cm in depth known as the fossa ovalis (Fig. 4). This hollow exists because the fascia lata, which would be expected to cover it, has disappeared into the depths of the groin to form the lacunar ligament. The fossa ovalis is filled with fat and some lymph nodes, and into it a femoral hernia presents from behind the inguinal ligament. The hernial lump, embedded in fat, can be easily overlooked when the hernia becomes strangulated.

The lacunar ligament The lacunar ligament appears in the photograph (Fig. 1) as a small dark grey triangular area of fascia, lying behind the shining fibres of the inguinal ligament and in front of the pecten pubis. It is derived, as has been shown, from the fascia lata of the thigh and comes into view when the backward extension of the transversalis fascia of the most medial part of the posterior inguinal wall has been dragged up from off its surface by the three-pronged retractor. This backward turn of the transversalis fascia, which hides and reinforces the lacunar ligament, gives rise to the femoral canal and it is the canal which conceals the lacunar ligament from view. The ligament lies in two different planes. The anterior part, fixed to the posterior border of the inguinal ligament, passes back in the same horizontal plane as the inguinal ligament until it reaches and blends with the pectineus muscle fascia along a line 1 cm below and in front of the pecten. From this line the posterior oblique part of the lacunar ligament, in company with the underlying pectineus muscle fascia, passes upwards and backwards to reach the on the pecten pubis. This fusion to the pectineus muscle fascia fixes the posterior arm of the curved edge 1 cm below and in front of the pecten. The curved edge is thereby lowered to lie in the same plane as the inguinal ligament. The posterior arm of the curved edge is also brought forward on the pectineus muscle fascia which allows the diameter of the curve to be shortened to 1 cm to fit closely around the medial border of the femoral sheath. The curved edge lies about 3 cm lateral to the pubic tubercle (Fig. 1). In femoral hernia the neck of the sac lies below the inguinal ligament, and is embraced by a firm circular fascial opening which has the curved edge of a ligament The inguinal and lacunar ligaments 247 1 cm in diameter on its medial side (Fig. 4). The medial curved edge of the opening, after removal of the hernial sac, is found to lie 1 cm or so below the pecten pubis, and about 3 cm lateral to the pubic tubercle, in a position and of a size identical with the curved edge seen in the photograph (Fig. 1). This curved edge, together with the neck of the sac, is divided to relieve pressure on strangulated bowel, and can now be accepted as the edge of the true lacunar ligament. Textbooks, however, show the curved edge of the lacunar ligament to be attached to the pectineal ligament on the pecten pubis. This is an easily understood but fundamental error, for although the lacunar ligament is attached to the pecten, its curved edge is not. Gimbernat thought that strangulation of the bowel occurred high up at the pecten, and this may have influenced surgeons and anatomists to misplace the curved edge there. It has been wrongly shown to lie at the pecten on the medial side of the femoral ring where a curved edge conveniently exists, but here it is widely separated from the . Usually, however, diagrams show it close to the femoral vein where the true curved edge lies, at a point 3 cm lateral to the pubic tubercle, but the curved edge is shown attached to the pecten where it must span the femoral ring at its widest part, where the ring measures about 2 cm at the medial edge of the . The diameter of the curve of the lacunar ligament wrongly placed here, between the pecten and the posterior border of the inguinal ligament, would be much too large to fit closely around the 1 cm wide medial border of the femoral sheath. Both these curved edges, sited on the pecten, would prove valueless as barriers between the abdomen and the thigh. A close examination of the curved edge shows that it is not a free, but an angled edge, for the fascia lata continues down from the edge of the curve to blend with the medial aspect of the femoral sheath, where in the thigh it is known as the cribriform fascia. The cribriform fascia, covering the medial border of the femoral sheath blends in the thigh with the thicker fascia lata in front of the sheath at the crescentic edge of the fossa ovalis (Fig. 4). An important function of the lacunar and inguinal ligaments, with their downward extensions of fascia lata, is to support the femoral sheath and hold open the lumen of the large thin-walled femoral vein, fixed within the walls of the femoral sheath, amid the stresses and strains of thigh movement and variations of intra-abdominal pressure and body posture. An important feature of groin anatomy is the backward turn, in unison, of its aponeurotic and fascial layers. The backward turn of the external oblique apo- neurosis gives rise to the inguinal ligament. The fascia lata turns back to form the lacunar ligament. The transversalis fascia of the medial part of the posterior inguinal wall turns back to form the femoral canal. For a better understanding of Figure 1, it might help to imagine that the retractors are withdrawn to permit normal relations to be restored. Removal of the three- pronged retractor allows the transversalis fascia of the medial part of the posterior inguinal wall and its backward extension, which forms the femoral canal, to fall down to cover the lacunar ligament. When the inguinal ligament is released from the pull of the artery forceps, the curved edge of the lacunar ligament can rise to fit into the right angle between the femoral canal and the two lateral compartments of the femoral sheath. The canal which forms the medial compartment lies above the 248 W. J. LYTLE lacunar ligament, while the two lateral compartments housing the femoral vein and artery lie below this level. Many details of groin anatomy have been omitted from this description. McVay & Anson (1940) described a supporting layer of fascia which descends from the transversus abdominis muscle to lie anterior to and fuse with the true transversalis fascia descending from behind the transversus aponeurosis. The or deep femoral arch is a band of white transverse fibres which stretches across the front of the lower limits of the posterior inguinal wall. This band is missing in Figure 1, having been detached by forcible retraction. The iliopubic tract is fixed below to the posterior border of the inguinal ligament and helps to seal off the inguinal canal from the thigh. The femoral canal andfemoral ring As is well known, the transversalis fascia of the main part of the posterior inguinal wall continues down behind the inguinal ligament as the anterior wall of the femoral sheath. It is rarely taught, however, that in the most medial part of the inguinal canal the downward passage of the transversalis fascia of the posterior inguinal wall is blocked by the lacunar ligament. Here the transversalis fascia descends to the posterior border of the inguinal ligament, where it is attached, and then turns back- wards, covering, concealing and giving support to the lacunar ligament, on its way to its final fixation to the pecten pubis. The three-pronged retractor in Figure 1 has raised this backward turn of the posterior inguinal wall, which it holds in its grasp, and has broken its attachment to the pectineal ligament on the pecten pubis. This backward turn gives rise to the femoral canal and it is the canal which conceals the lacunar ligament from view. The canal, the medial compartment of the femoral sheath, is seen in the photograph (Fig. 1) to lie above the lacunar ligament, while the two lateral compartments, containing the femoral vein and artery lie below this level. The canal opens above into the abdominal cavity by the large femoral ring, and below narrows markedly as it ends above the curved edge of the lacunar ligament, where it joins the middle compartment of the femoral sheath. In some cases the lower blind end of the canal projects into the thigh between the curved edge and the middle compartment of the femoral sheath; this is a source of groin weakness which may predispose to the onset of a femoral hernia. The femoral ring lies at the level of the pectineal ligament on the pecten pubis which forms its posterior boundary. The ring opening is roughly triangular with its lateral boundary formed by the external iliac vein. The anterior and posterior boundaries approach each other medially where the apex is blunted by the presence of the curved edge of a variable ligament, composed of transversalis fascia, which is not the lacunar ligament. The anterior boundary of the femoral ring is usually given as the inguinal ligament, which here measures from 1 to 1l5 cm in breadth, but it is not stated whether the anterior or posterior border of the inguinal ligament is the chosen anterior boundary of the femoral ring. In addition, the inguinal ligament lies cm or so below the pecten pubis and is separated from the ring opening by the posterior inguinal wall here turning back to form the femoral canal. A more realistic anterior boundary might possibly be the posterior inguinal wall 1 cm above the inguinal ligament. At this level, on the same horizontal plane as the pecten pubis, The inguinal and lacunar ligaments 249 the posterior inguinal wall is strengthened by the iliopubic tract and the of the transversus and internal oblique muscles approaching insertion into the pecten. Indeed, a common operation for closure of the femoral ring in femoral hernia is suture of the conjoint tendon by the shortest route to the pectineal ligament immediately opposite. The triangular femoral ring, on this basis, has its widest antero-posterior measurement of about 2 cm at the medial border of the external iliac vein. The medio-lateral measurement is usually also about 2 cm.

Femoral hernia In femoral hernia the defect is not at the large femoral ring, where, in adults, the surgeon, operating from within the abdomen, can pass his finger freely down into the canal. The hole or perforation is in the fascial layers of the groin below the inguinal ligament. It is assumed that a peritoneal protrusion, usually covered by extra- pzritoneal fat, pushes its way down the canal, separates the curved edge of the lacunar ligament from the femoral sheath, bursts through the transversalis fascia of the blind lower end of the canal, then through the cribriform fascia extending down from the curved edge of the lacunar ligament and finally through a covering layer of groin fascia. The hole in these three fascial layers fused together is circular in outline, with a firm fibrous edge which surrounds the neck of the hernial sac. The opening lies just below the inguinal ligament, about 3 cm lateral to the pubic tubercle, and usually measures 1 cm in diameter, too small to admit more than the tip of the little finger (Fig. 4). The small circular opening, which has the same diameter as the curved edge of the lacunar ligament forming its medial boundary, is of vital importance, for here strangulation of the bowel occurs which is relieved by dividing the neck of the sac and the lacunar ligament on the medial side of the opening. I named this opening 'the femoral hernial orifice' (1957) to distinguish it from the large femoral ring above. This opening, which lies at the constriction rings on strangulated bowel, has received little attention. This may be because of its small size or the fact that the edges, after removal of the sac, tend to fall together to make the opening indistinct; or more likely because surgeons, influenced by Gimbernat's teaching, look for the cause of strangulation higher up at the femoral ring. The femoral hernial orifice is subject to variation, for in longstanding cases the curved edge of the lacunar ligament may be stretched well beyond its 1 cm diameter to make the opening large enough to admit the index finger or thumb; the orifice may also lie 1 to 2 cm below the inguinal ligament and, here, the cribriform fascia, extending down from the curved edge of the lacunar ligament, lies on its medial side. The boundaries of the orifice are: on the medial side, the curved edge of the lacunar ligament; in front, the crescentic edge or falciform margin of the fascia lata of the femoral sheath; laterally, the crescentic edge and cribriform fascia; and posteriorly, the fascia over the pectineus muscle (Fig. 4). A repair operation is necessary for femoral hernia because of the risk of strangula- tion and the failure of a truss to keep the sac empty. There is the 'high' operation which aims at closure of the femoral ring from within the abdominal cavity, and the 'low' operation where the femoral hernial orifice is closed from below the inguinal ligament. The high operation requires an incision through the abdominal wall or inguinal 250 W. J. LYTLE

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Fig. 4. The femoral hernial orifice encircles the neck of the hernial sac which is shown in interrupted lines, with the curved edge of the lacunar ligament forming its medial boundary. canal to gain access to the femoral ring. The posterior wall of the inguinal canal with the conjoint tendon is stitched to the pectineal ligament on the pecten pubis, but as the sutures are under some tension, damage to the posterior inguinal wall may result and lead to a direct inguinal hernia (McNaught, 1956). To avoid this, a flap of fascia hinged on the pectineal ligament can be raised and sutured into position, as a lid to cover the femoral ring. In the low operation the femoral hernial orifice is closed by sutures, an easy procedure which reunites the curved edge of the lacunar ligament to the crescentic edge of the femoral sheath and gives as good, if not better, results as the high operation. In strangulated hernia division of the lacunar ligament from below the inguinal ligament entails no risk of haemorrhage from an abnormal .

SUMMARY The inguinal and lacunar ligaments form a strong protective diaphragm between the abdomen and the thigh. The inguinal ligament provides a broad aponeurotic floor for the inguinal canal which keeps its anterior and posterior walls apart to give roomy passage for the spermatic cord. The ligament is much thicker and stronger than the external oblique aponeurosis from which it arises and this is due to the The inguinal and lacunar ligaments 251 obliquity of the aponeurotic fibres entering it, which allows of a wide area of aponeurosis to contribute to its bulk. The lacunar ligament, derived from the fascia lata of the thigh, is attached in front to the posterior border of the inguinal ligament and although it ends behind at the pecten pubis it is fused, as is also the inguinal ligament, to the pectineus muscle fascia over an area 1 cm in width before reaching the pecten. This fusion fixes the curved edge 1 cm below and also in front of the pecten, thereby lowering it to the level of the inguinal ligament, and also shortening its diameter to 1 cm to fit closely around the medial border of the femoral sheath and the femoral vein within the sheath. The attachment of the inguinal and lacunar ligaments to the femoral sheath seals off the abdominal cavity from the thigh, and holds open the large thin-walled femoral vein as it passes, often under stress, from the thigh to the abdomen. The lacunar ligament is weaker than the inguinal ligament, but is reinforced by the transversalis fascia of the posterior inguinal wall which turns back at the posterior border of the inguinal ligament on the upper surface of the lacunar ligament to form the femoral canal. In femoral hernia, a peritoneal protrusion, covered by extra-peritoneal fat, pushes down into the femoral canal, separates the curved edge of the lacunar ligament from the femoral sheath, and breaks through three fascial layers in the groin to present as a hernia below the inguinal ligament. The circular hole, usually 1 cm in diameter, named the femoral hernial orifice, through which the rupture emerges, lies round the neck of the hernial sac, and here strangulation of the bowel occurs, which is relieved by dividing the neck of the sac and the curved edge of the lacunar ligament which forms the medial boundary of the opening. I am greatly indebted to Dr Arthur Ross Wilcock for the photograph which reveals much of the hidden anatomy of the groin and to Mr J. T. Rowling for useful comments.

REFERENCES COOPER, A. (1844). The Anatomy and Surgical Treatment of Abdominal Hernia. Philadelphia: Lea and Blanchard. GIMBERNAT, DON A. DE (1795). A New Method of Operating for Femoral Hernia. English translation. London: J. Johnson. LYTLE, W. J. (1957). Femoral hernia. Annals of the Royal College of Surgeons of England 21, 244-262. MADDEN, J. L., HAKIM, S. & AGOROGIANNIS, A. B. (1971). The anatomy and repair of inguinal . Surgical Clinics ofNorth America 51, No. 6, 1269-1292. McNAUGHT, G. H. D. (1956). Femoral hernia. The operation of McEvedy. Journal of the Royal College of Surgeons of Edinburgh 1, 309-315. MCVAY, C. B. & ANSON, B. J. (1940). Aponeurotic and fascial continuities in the abdomen, and thigh. Anatomical Record 76, 213-231.