Introduction

• Cause: surgical trauma; incisional infection: one of the most common complications of abdominal laparotomy. Defect in abdominal wall permits eventration of viscera into subcutaneous space.
• Signs: visible or palpable swelling at incision site, may be associated with wound drainage, infection or dehiscence; abdominal pain or discomfort.
• Diagnosis: observation, palpation, ultrasound, fine needle aspiration; surgical exploration.
• Treatment: none → surgical repair with a mesh implant.
• Prognosis: fair → grave if evisceration occurs.

Pathogenesis

Etiology

• Surgical incision combined with any or all of the following:
  • Excessive tissue trauma → lowers local defense mechanisms.
  • Poor suture technique:
    • Many different types of suture material and suture patterns have been used and investigated in the closure of the linea alba.
    • Many surgeons use a simple continuous suture pattern Surgery: suture patterns - basic patterns which has been found to have a high level of bursting strength.
    • The optimal tissue bit size in adult horses has been determined as 15 mm from the edge of the linea alba.
  • Wound contamination and infection → bacterial numbers overwhelm local defense mechanisms. Incisional infection is common prior to herniation with one paper demonstrating a 62.5 times more likely risk of developing a hernia with incisional infections.
  • Excessive movement at the wound site, eg due to pain or exercise.
  • Drainage from the incision (an indicator of abnormal wound healing).
• Delayed wound healing Wound: healing - factors → weakened abdominal fascia → herniation of omentum +/- intestine.
• Flank incisions have a greater likelihood of creating dead space, tissue necrosis and muscle trauma during surgery. One paper reported an 88% incidence of complications in celiotomy incisions versus the ventral midline.

Predisposing factors

General

• Abdominal surgery.

Specific

• Repeat abdominal surgery (only 70% of fascial strength returns after 1 year). Various studies have suggested a 2-3 times increase after re-laparotomy.
• Surgery lasting >2 h.
• Difficulties associated with anesthetic recovery.
• Incisional edema may affect local tissue oxygen tension and delay wound healing, suppress local immune function, and provide an optimal environment for bacteria.
• Incisional drainage - especially if purulent rather than serosanguinous.
• Post-operative leukopenia Blood: leukocytes.
• Post-operative pain.
• Old age.
• Large size.
• Uncontrolled post-operative exercise.
• Inappropriate suture material - type or size Surgery: suture materials - overview. Use of chromic gut suture in the linea alba.
• The occurrence of incisional complications, including herniation, after closure of equine celiotomies with USP 7 polydioxanone Surgery: suture materials - overview sutures was recently found to be low.
• Incisional infection (reported in 25% of herniations).
• Use of near-far-near suture pattern Surgery: suture patterns - basic patterns.
• Excessive dissection of the linea alba prior to closure.

Pathophysiology

• Incisional hernias occur in 5.7-18% of horses following ventral midline celiotomy.

Incisions along the ventral midline generally carry a lower rate of complications than incisions located elsewhere on the abdomen, eg flank. This is not, however, the case for incisional herniation which appear to be more common post-ventral midline celiotomy for colic surgery. Incisional hernias are also more common following other incisional complications, particularly serous or purulent incisional drainage.

• Enterotomy or enterectomy, in which there is potential contamination from spilled intestinal contents, does not seem to increase the risk of wound complications.
• Incisional hernia may be classified on a scale for wound breakdown:
  • Superficial dehiscence - separation of the skin and subcutaneous tissue alone.
  • Herniation - palpable or visible defect in the abdominal wall with overlying intact skin.
  • Partial dehiscence - separation of the skin, subcutaneous tissue and body wall along part of the incision line.
  • Complete dehiscence - separation of all layers along the entire incision line → evisceration.
• Up to 20% of horses that develop incisional hernias do not have a single hernia but often multiple small hernias situated along the incision.

Timecourse

• May occur up to 2 months following surgery.

Diagnosis

Treatment

Prevention

Outcomes