J. Anat. (1974), 118, 2, pp. 241-251 241 With 4 figures Printed in Great Britain The inguinal 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 hernia, described in detail the crural arch, subsequently known as Poupart's ligament, and now the inguinal ligament. He described the crural arch as a remarkable plait or duplicature backwards of the aponeurosis of the external oblique muscle, more manifest towards the os pubis, 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 pubic tubercle, the remainder being named its pectineal part, but as this name is also given to the lacunar ligament 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 femoral sheath. This is, in fact, thefascial lacunar ligament derived, as will be shown, from the fascia lata 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 femoral hernia where gangrenous bowel requires resection by a combined approach through the abdominal wall and below the inguinal ligament. The upper curved edge, viewed from within the abdominal cavity, lies on the medial side of the femoral ring, 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 groin adhere firmly and resist separation. In the living body, at inguinal hernia 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 transversalis fascia 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 abdomen 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.