Examination of the hernia

In the vast majority of cases, gentle pressure on the protruding swelling will reduce the hernia, allowing identification of the hernial ring, which should be assessed for size, shape and rigidity.

Incarcerated hernias present as tense, painful swellings which are usually irreducible. Occasionally gas in the entrapped intestine may have been dispersed during transport to a surgical facility or by gentle pressure allowing reduction to be achieved. Although the immediate risk to the foal’s life may have been removed, whenever possible repair of the hernia should be carried out as soon as possible. Immediate repair will allow identification and removal of necrotic intestine which will eventually rupture.

Incision of the hernia sac and careful examination of the caecum and small intestine should be performed to rule out the possibility of ischaemic compromise which is particularly likely with a Richter hernia. Even if ischaemic damage is not considered likely, any delay in repair of the hernia should be kept to a minimum because of the possibility of a further episode of incarceration which on that occasion may progress to strangulation.

Closed reduction

A wide variety of methods of treatment have been used in the past, including blisters, transfixing skewers and wooden or metal clamps. Although clamps are still in use, the method of closed reduction most often used is the application of elastrator rings at the base of the sac after ensuring that any contents have been returned to the abdomen. There may be some oedema between the rubber ring and the abdominal wall on the day after application, but any local inflammation usually resolves in 7–10 days. Separation of the hernial sac vestige should be allowed to occur without assistance and takes approximately 3–4 weeks. This technique depends on subcutaneous fibrous scar tissue to obliterate the defect, and is only useful in treating small one-finger defects.

With the availability of safe anaesthetic techniques and improved suture materials, there is little indication for employing a method which is less than certain to correct the hernia. Open reduction, whereby the defect in the abdominal wall is closed by apposing the edges of the ring or by the use of an inlay prosthesis is a much more satisfactory method of treatment.

Open reduction

The surgery is performed under general anaesthesia and strict aseptic conditions with the patient in dorsal recumbency. An elliptical skin incision is made around the umbilical scar extending 2 cm beyond the margin of the hernial ring cranially and caudally. Care must be taken to avoid removing too much skin. The peritoneal sac is carefully dissected away from the overlying skin and the abdominal wall until the margin of the ring can be identified. Unless there is residual umbilical stalk present, or ischaemic damage to the intestine is suspected, the hernial sac need not be incised but rather simply returned to the abdominal cavity.

The majority of hernial rings are oval in shape and their edges are sufficiently pliable to allow them to be closed by a series of overlapping mattress (Mayo) sutures of absorbable or non-absorbable material.

The sutures are inserted 1–2 cm from the margin of the ring and are carried through the full thickness of the abdominal wall on both sides of the ring. A finger inserted into the inverted sac serves to guide the needle and prevent inadvertent damage to the intestine (Figure 4.1). The ends of each suture are held with haemostats until they are all in place. Simultaneous traction on the sutures overlap the edges of the ring and this is maintained while each individual suture is tied. The subcutaneous tissue is apposed with a continuous suture of polyglactin, and the skin with a subcuticular suture of the same material. The application of an elastic bandage encircling the abdomen (or a stent bandage in the case of small hernias) will provide protection from contamination and eliminate dead space.

With large hernial rings, it may be necessary to bridge the defect with a prosthetic mesh or gauze. The mesh, which must be inert and nonreactive to the tissues, stimulates fibroplasia, resulting in it being enveloped in a thick fibrous bed that fills the defect and strengthens the abdominal wall.

The mesh is best placed in an extraperitoneal position between the internal rectus abdominal sheath and the peritoneum. The peritoneal sac is dissected down to the hernial ring and inverted into the abdominal cavity as described above. If the sac is sufficiently large, the mesh can be placed within it (Figure 4.2), but if it is not, the peritoneum is reflected peripherally from the deep fascial sheath of the rectus abdominis muscle for 1–3 cm to create a space for the mesh. The mesh is cut so that it overlaps the margin of the ring by the same amount. The sutures are preplaced before tying. Sufficient tension is applied so that the mesh is kept taut and flat. The subcutaneous tissues and skin are then carefully apposed over the mesh.