An inguinal hernia is defined as a protrusion of part of the contents of the abdomen through the inguinal region of the abdominal wall. Inguinal hernias are common throughout the world, but precise figures for prevalence and incidence are not available. Hernias in the inguinal region account for approximately 75 per cent of all forms of hernias and are more common in males than females.

Inguinal hernias are classified as indirect, direct, or recurrent, and may be reducible or irreducible. The possible contents of an inguinal hernial sac and their viability also allow further descriptive terms (Table 1) 403.

Consideration of the anatomy of the inguinal region is fundamental to understanding both the development of inguinal hernias and the methods of surgical repair.

The inguinal canal passes obliquely downwards and medially from the internal to external inguinal rings. In adults the inguinal canal is 3 to 4 cm long. The normal contents of the inguinal canal are, in the male, the spermatic cord and the ilioinguinal nerve; in the female they are the round ligament and the ilioinguinal nerve.

Anteriorly is skin, superficial fascia, and external oblique aponeurosis. Posteromedially is the conjoined ‘tendon’ (rarely tendinous) formed from the common insertion of the internal oblique and transversus abdominus muscles to the pubic crest. Posterolaterally, under the arching structures of the conjoined tendon, lies the transversalis fascia. Inferiorly is the inguinal ligament, formed from the inferior free border of external oblique aponeurosis. According to North American texts, immediately deep to the inguinal ligament is a structure named the iliopubic tract (an aponeurotic band formed from the inferior margin of the transversus abdominis muscle and aponeurosis). The iliopubic tract extends from the fascia of iliacus and psoas laterally to the pectineal ligament medially, and is described in the Cooper/McVay repair. However, the iliopubic tract is not referred to in English anatomy texts, and does not feature in the Shouldice method of repair.

The internal ring is the point at which the spermatic cord or round ligament passes through the transversalis fascia to enter the inguinal canal. The transversalis fascia forms a U-shaped sling around the internal ring. This sling has two crura: the antero-superior crus is in continuity with the transversus abdominis muscle and aponeurosis, and the posteroinferior crus is attached to the inguinal ligament/iliopubic tract. This U-shaped sling acts as a shutter when the transversus abdominis muscle contracts, preventing herniation in normal individuals.

The internal ring is bordered inferiorly by the inguinal ligament, medially by the inferior epigastric vessels, and superiorly and laterally by internal oblique and transversus abdominis. The surface marking of the internal ring, crucial in differentiating indirect from direct inguinal hernias, is 1.25 cm superior to the point midway between the anterior superior iliac spine and the pubic tubercle.

The external inguinal ring is a V-shaped defect immediately superior to the pubic tubercle, with the apex of the V superolaterally.

It is important to note the occupational history of the patient. Hernias often appear or become symptomatic in relation to strenuous physical activity. The symptoms of a hernia may limit ability to work: this is an indication for expeditious repair.

Pain or discomfort may be present before a lump is noted by the patient. If pain develops in association with irreducibility of a previously reducible hernia, the contents must be assumed to be strangulated and emergency operation is indicated.

Many hernias are painless, and the patient notices a lump in the groin or scrotum. Some patients remark that the lump disappears after lying down or is largest at the end of the day.

Colicky abdominal pain, vomiting, abdominal distension, and absolute constipation are the classical symptoms of intestinal obstruction. One or more of these symptoms is likely if a hernia causes intestinal obstruction.

Specific symptoms relevant to the development of hernias are any that indicate abdominal straining or raised intra-abdominal pressure. Thus, it is pertinent to enquire about persistent cough (commonly chronic bronchitis), difficulty with micturition (especially in middle-aged and elderly men) and constipation (more specifically, straining at defecation).

The diagnostic signs of a hernia are a lump that is reducible and has an expansile cough impulse. Accurate diagnosis that such a swelling is an inguinal hernia depends upon its position. Whether direct or indirect, inguinal hernias pass through the external inguinal ring and are therefore always reduced through the abdominal wall above and medial to the pubic tubercle. However, large inguinal hernias often descend into the scrotum and may lie below and lateral to the pubic tubercle (Fig. 2) 1426.

Both inguinal regions, and the scrotum must be examined with the patient standing and lying supine. If the former position is omitted small hernias, saphena varices, and varicoceles may be missed. The position, temperature, tenderness, shape, size, and consistency of groin and scrotal lumps must be determined during the course of clinical examination.

Look for scars or any skin abnormalities as well as an obvious lump in either groin or the scrotum. Test whether a lump appears in the inguinal or femoral regions when the patient coughs.

If a hernia is apparent on inspection, attempt to reduce it and decide whether it is inguinal or femoral by defining its relationship to the pubic tubercle. If the hernia is inguinal, determine whether it is indirect or direct (see Table 2 404). If a scrotal swelling is present, determine whether or not the lump has an upper border. If the lump has no upper edge, it is likely to be an inguinoscrotal hernia. If not, decide whether the lump is in the spermatic cord, the epididymis, the testis, or skin and fascial layers of the scrotum.

A hernia that contains gut may be resonant, and bowel sounds may be audible over it.

This question causes considerable anxiety, but is of little clinical significance. Not only does preoperative assessment of the type of inguinal hernia not affect management decisions, but even the most experienced clinicians reach the wrong diagnosis.

An indirect inguinal hernia passes through the internal ring (i.e. lateral to the inferior epigastric vessels); direct inguinal hernias pass through defects in the transversalis fascia medial to the inferior epigastric vessels. Thus the cardinal distinguishing sign is whether or not the hernia is controlled at the internal ring. This is established by reducing the hernia fully, then applying pressure over the internal inguinal ring (1.25 cm above the midpoint between pubic tubercle and anterior superior iliac spine). If the hernia is controlled it is indirect; if not it is direct. Other features that distinguish indirect from direct inguinal hernias are summarized in.

Careful examination, with particular attention to anatomical relationships will distinguish inguinal hernia from most other lumps in the groin. A list of differential diagnoses, with distinguishing features is given in Table 3 405.

Ideally all inguinal hernias should be repaired, but operation may be inappropriate for a few very unfit patients. In such cases the use of a truss may be considered. If prescribed, a truss must be properly fitted and maintained to avoid the potentially lethal application of a truss to a hernia that is not reduced. This may precipitate strangulation of the contents of the hernia.

There are many different techniques for the repair of inguinal hernias. Whatever method is used, meticulous technique is essential. The principles of repair are excision or reduction of the hernial sac, and repair of the posterior wall of the inguinal canal.

For simple indirect hernias the sac is dissected out of the cord, transfixed at the internal ring, and excised. Sliding indirect hernias require dissection of the sac out of the cord so that the sac can be fully reduced, sometimes with excision of part of the sac distal to the sliding viscus. With large inguinoscrotal hernias it may be prudent to divide the sac at the internal ring, transfixing the proximal end and leaving the distal end open. Dissection of the sac of a large inguinoscrotal hernia out of the spermatic cord may result in a postoperative scrotal haematoma, and compromise of the blood supply to the testis.

In all but very large direct hernias, the sac does not need to be excised. The hernia is reduced and the defect in the transversalis fascia closed either as part of the Shouldice technique, or prior to other methods of strengthening the posterior wall of the inguinal canal. If an obvious direct hernia is found, the spermatic cord must be opened and the cord carefully inspected at the internal ring. Even if there is no true indirect sac, there is usually a small crescentic peritoneal reflection (the remnant of the processus vaginalis). This reflection should be swept off the cord.

The methods of repair may be classified in two broad groups: approximation or reinforcement of the structures of the posterior wall of the inguinal canal. The Shouldice technique combines elements of reinforcement with approximation, and is considered separately.

The posterior wall of the inguinal canal may be repaired by approximation of the transversus abdominis aponeurotic arch either to the inguinal ligament (the Bassini technique, which has many variants) or to the iliopubic tract/Cooper's ligament (the McVay method). Both of these techniques were originally described using interrupted sutures. A relieving incision in the lateral aspect of the inferior part of the anterior rectus sheath is often required to prevent tension in the repair (Fig. 3) 1427.

The posterior wall of the inguinal canal may be reinforced without tension (and therefore without requiring a relieving incision) by a loose but closely applied darn, the Shouldice method, or insertion of a prosthetic mesh. Prosthetic meshes are rarely used in primary hernia repairs, but are advocated by some surgeons for the repair of recurrent hernias.

Many variants of darn have evolved. Darns are between either Cooper's ligament or inguinal ligament and the conjoined tendon. It is important that the darn is secured superiorly to the tendinous aponeuorosis of internal oblique/transversus abdominis rather than to the muscle. A variety of non-absorbable suture materials have been used. Initial strength is obtained by the darn itself. This strength is increased by fibrosis around the suture material used for the darn. Darns all share three features. First there must be no tension. This avoids the risks of either sutures tearing or development of a femoral hernia (if the inguinal ligament is used). Second, the suture should be continuous. This spreads the tension evenly. Finally, the lattice should have no defects.

The method used at the Shouldice clinic differs from other repairs in two respects: the spermatic cord is freed at the internal ring by complete division of the cremaster muscle, and the posterior wall of the inguinal canal is repaired by dividing the transversalis fascia from the pubis to adjacent to the inferior epigastric vessels (which are preserved). The transversalis fascia is then ‘double-breasted’. A continuous suture is employed starting at the pubic bone, attaching the free edge of the inferolateral flap to the undersurface of the superomedial flap of transversalis fascia. This extends to the internal ring, and the same suture is used to attach the free edge of the superomedial flap to the deep surface of the inguinal ligament working back to the pubic bone. A second suture runs from internal ring to the pubic bone and back again, bringing fibres of internal oblique and transversus abdominis to the deep aspect of the inguinal ligament.

The true incidence of recurrence following repair of inguinal hernias is difficult to determine: prolonged follow-up is necessary, and this is not feasible in most centres for logistic and financial reasons. In addition, there may be a bias towards reporting only good results. With these two caveats, the recurrence rates vary from 0.6 per cent reported in a personal series of 13 108 hernia repairs by Glassow to an estimate of 10 per cent of all hernia repairs performed in the United States of America.

Poor surgical technique is the most common cause of recurrence following primary repair of an inguinal hernia. The evidence for this is the wide variation in recurrence rate between reported series.

Wound infection following primary repair is associated with a high recurrence rate: meticulous asepsis is essential in hernia surgery. Persistent straining (cough, urinary outflow obstruction, or straining at defecation) is also a risk factor for the development of a recurrent hernia.

Direct repair after reopening the inguinal canal, except by the Shouldice method, is associated with a re-recurrence rate of greater than 2 per cent in all series. In contrast, insertion of a prosthetic mesh via a preperitoneal approach has a re-recurrence rate of less than 2 per cent in all series except one. However, no studies have compared these two methods directly.

The first step is to define the anatomy. This is often difficult because of the distortion and scarring caused by previous operations. Early identification of the external oblique aponeurosis well superior to the inguinal canal, and sharp dissection with a scalpel are useful techniques.

Small defects may be repaired by direct suture or onlay darn. For larger defects, the choice is between an onlay darn or insertion of a prosthetic mesh. Orchidectomy in the male (usually elderly) enables complete closure of the posterior wall of the inguinal canal.

The skin incision for the preperitoneal approach is placed superior to that used for primary repair of the hernia, and the preperitoneal space deep to the abdominal wall muscles is entered via an oblique incision in the rectus sheath with medial retraction of the rectus abdominis muscle (the McEvedy approach). This is an adaption of an earlier technique of lateral retraction of the rectus muscle (Cheatle/Henry). These approaches were originally described for the repair of femoral hernias, but access to the inguinal region is excellent, especially when the inguinal canal has been distorted by previous operations.

The principle of the repair is to inlay a piece of prosthetic mesh (many types are available), securing the mesh to cover the inner aspect of the defect. This inlay technique has an obvious mechanical advantage over onlay meshes (placed in the inguinal canal) in that intra-abdominal pressure will plaster the former against the abdominal wall musculature and tend to push out the latter. Indeed some surgeons have placed prosthetic mesh via the preperitoneal approach without suturing, relying on intra-abdominal pressure to keep the mesh in place.

The main hazard of insertion of a large piece of mesh is infection. Scrupulous asepsis and prophylactic administration of broad-spectrum antibiotics are essential.

The recent rapid increase in laparoscopic access for surgical procedures has included use of this method in repair of inguinal hernias. A herniotomy equivalent is easily achieved, involving invagination, ligation, and excision of the hernia sac. This is only appropriate in indirect hernias with no muscular defect in the abdominal wall. Laparoscopic herniorrhaphy by insertion of synthetic mesh to eliminate the muscular defect associated with an inguinal hernia is now the procedure most widely used by surgeons who repair inguinal hernias laparoscopically.

However, all that has been proved to date is that the inguinal region can be operated on using laparoscopic methods. Proper evaluation must include comparison with standard methods in respect of early complications, hernia recurrence, and cost/benefit analysis. Such trials are in progress at this time.

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