1 Surgical Anatomy

A clear understanding of the anatomy of the abdominal wall is critical when performing a component separation operation. The two vertically oriented rectus abdominis muscles, with their overlying anterior rectus sheaths should normally lie side by side in the midline. In between the rectus muscles is the tendinous linea alba, which functionally is actually the tendinous insertion of the fascial extensions of the six lateral abdominal wall muscles (bilateral external oblique, internal oblique, and transverses abdominis). A midline incisional hernia is caused by a disruption of the linea alba, which in turn leads to unopposed contraction of the lateral abdominal wall muscles. It is this constant unopposed pull from the lateral muscles in combination with intraperitoneal pressure that leads to the gradual increase in size of these hernias and ultimately loss of abdominal domain. The position of the arcuate line is also important to understand. The arcuate line lies approximately three fourths of the way from the pubis to the umbilicus, or to use a bony anatomic landmark, approximately 2 cm cephalad to a line drawn between the two anterior superior iliac spines. Below this line there is no posterior rectus sheath (Cunningham, 2004). There is also a small triangular muscle called the pyrimidalis that overlies the most inferior portion of the rectus muscles just as they attach onto the pubis. This muscle is not relevant clinically.

The main blood supply to the rectus abdominis muscles is from the superior and inferior epigastric arteries, with the inferior epigastric being more dominant. The entire muscle can easily survive however on either blood vessel. There are additional vascular contributions from the intercostal arterial branches that come in laterally in a segmental fashion. The blood supply to the lateral musculature comes from intercostal branches that travel deep to the internal oblique muscle in the so-called neurovascular plane. In this plane are also the nerves to the abdominal wall that are branches of the lower six thoracic and the first lumbar segmental nerves.

2 Preoperative Considerations

The preoperative evaluation should include a complete medical history that includes any operative reports from previous operations. In cases where there have been previous hernia repairs, it is important to know what type of mesh repairs have been done, including the specific brand of mesh and the plane in which the mesh was placed and whether or not a component separation has been previously attempted. It should be noted in the history whether or not there were wound complications or infections after any of the previous operations.

Certain comorbidities are associated with higher rates of complications, and if any of these comorbidities can be managed before the surgery, every effort should be made to do so. Examples include losing weight, controlling diabetes, quitting smoking, maximizing nutritional status, maximizing a patient’s cardio/pulmonary health, and taking appropriate prophylactic measures for thromboembolic disease.

It should be noted that in many circumstances, although patients can be quite miserable, incisional hernia repairs can be categorized as elective surgery. Those patients with hernia defects with a very wide base are at a low risk for bowel strangulation and obstruction. In patients like this, with non–life-threatening hernias, where the extent of their comorbidities carry an unacceptably high mortality risk, surgery should be avoided. One particular comorbidity, that of being super-obese (body mass index [BMI] >45), in addition to other general morbidities, carries a very high risk of hernia recurrence, reported to be as high as 50% (Vargo, 2008). In these patients, the risk-to-benefit scale is certainly tilted toward risk, and a serious effort at weight loss should be attempted before opting for elective surgery.

3 Operative Steps

The first step in performing a component separation is lysis of adhesions from the bowel to the undersurface of the abdominal wall. This allows for a good underlay of any mesh that may be used but also helps to untether the abdominal wall musculature and allow it to advance toward the midline. The next step is identification of the healthy fascial edges. This is performed by undermining the skin and subcutaneous fat until healthy rectus abdominis anterior fascia is identified. It is important to do this very carefully and avoid getting underneath the anterior rectus fascia. It is also important not to confuse dense scar tissue from healthy fascia, which is a common mistake that leads to recurrence over time as that dense scar tissue slowly remodels and ultimately gives way. In the case of skin graft or secondarily healed scar on top of bowel there are two options. One option is to remove the skin graft or scar completely with sharp dissection. This can sometimes be difficult and may lead to enterotomies. If it becomes clear that this technique is too risky, then another option is to leave the skin graft or scar on the bowel and simply de-epithelialize it. This is done with a number 10 scalpel blade by tangentially shaving off the epidermis, leaving what is left of the dermis or the scar tissue behind. At the periphery, the normal skin and subcutaneous fat can be undermined in the usual fashion until healthy fascia is identified.