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Posterior Component Separation With Transversus Abdominis Muscle Release
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Clinical Anatomy
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Retrorectus repair requires a thorough knowledge of the relative anatomy of the myofascial components of the abdominal wall.
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The rectus abdominis, a long, broad, straplike muscle, is the principal vertical muscle of the anterior abdominal wall. Its origin is at the pubic symphysis and pubic crest. The muscle is inserted into the cartilages of the fifth, sixth, and seventh ribs. The rectus abdominis is three times as wide superiorly as it is inferiorly.
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The rectus abdominis is segmentally innervated by the thoracoabdominal nerves T7 through T12. The main trunks of the intercostal nerves pass anteriorly from the intercostal spaces and run between the internal oblique and transversus abdominis muscles in a so-called neurovascular plane. The inferior intercostal, subcostal, and lumbar arteries accompany the nerves of this plane.
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The intercostal nerves pass just medial to the linea semilunaris at the lateral edge of the rectus muscle and along the posterior rectus sheath and penetrate the posterior leaflet of the internal oblique muscle to segmentally innervate the rectus muscle. These nerves mark the lateral extent of the retrorectus space. They must be carefully identified and preserved in any retromuscular dissection to avoid denervating the rectus muscle.
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The rectus sheath is the strong, incomplete fibrous compartment for the rectus abdominis muscle. It forms by the fusion and separation of the aponeurosis of the lateral abdominal muscles.
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The internal oblique aponeurosis splits into two layers, one passing anterior to the rectus muscle and the other passing posterior to it. The posterior layer joins with the aponeurosis of the transverse abdominis muscle to form the posterior wall of the rectus sheath. Muscle fibers of the transversus abdominis end in an aponeurosis, which contributes to the formation of the rectus sheath.
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One important consideration for the posterior component separation is the fact that in the upper third of the abdomen, the posterior leaflet of the internal oblique and the transversus abdominis muscle extends medially beyond the linea semilunaris as a primary muscular component and not as fascia ( Fig. 5.1 ). This allows the surgeon to access lateral muscles (posterior leaflet of the internal oblique and transversus abdominis) via a medial approach.
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Understanding the anatomic contributions of the lateral muscles to the posterior rectus sheath provides an important understanding of what each of their contributions are to allowing the midline fascia (linea alba) to advance to the midline and the posterior rectus sheath.
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Initially it was thought that the transversus abdominis muscle was the key component to midline fascial advancement during a posterior component separation. However, with refined understanding of abdominal wall anatomy, this may no longer be correct.
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The release of the posterior leaflet of the internal oblique provides the key myofascial separation that allows the midline fascia to advance and be “released” of its posterior attachments.
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The release of the transversus abdominis allows advancement of the peritoneum and posterior components to safely provide a tension-free closure of the posterior rectus sheath, excluding the mesh from the viscera.
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One of the tenets of a posterior component separation is to gain access to the preperitoneal and retroperitoneal space in the lateral abdominal wall. This should be attempted as far laterally as possible within the retrorectus space without injuring the intercostal nerves. Because the peritoneum is deeply invested in the posterior rectus sheath medially, it is technically easier to gain access in the lateral aspect of the retrorectus space. This access avoids making excessive holes in the peritoneum during the dissection.
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Preoperative Considerations
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Preoperative Imaging
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Routine abdominopelvic computed tomography (CT) imaging should be performed. CT delineates all abdominal wall defects, assesses the integrity of the remaining abdominal wall musculature, allows for detection of previous synthetic meshes or occult infection, and facilitates perioperative planning.
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Preoperative Optimization
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Nutritional evaluation and medical weight loss counseling for obese patients are paramount, and weight loss surgery should be considered for patients who are eligible.
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Smoking cessation is mandatory and is confirmed with a urine cotinine level.
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Cardiac and pulmonary status should be assessed and optimized.
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Diabetes control is verified with routine hemoglobin A 1c levels; cases are postponed if hemoglobin A 1c is greater than 8.0.
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Choosing the Type of Mesh
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Multiple factors are considered when choosing the appropriate mesh.
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Antiadhesive barrier meshes are unnecessary in this approach. Because such meshes do not allow significant tissue ingrowth on one side, they might have a deleterious effect with respect to seroma formation and mesh tissue integration when placed in the retromuscular location.
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In contaminated cases, a biologic or bioabsorbable synthetic mesh can be used.
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In clean cases, a synthetic mesh is appropriate.
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A large-pore synthetic mesh of at least 30 × 30 cm is sufficient in most patients.
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I use a medium-weight polypropylene mesh (40–50 g/m 2 ) for most cases, particularly in contaminated cases.
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In cases with a very large defect, a defect that will not come together, or a very obese patient, central mesh fractures can occur with lighter-weight materials, and use of a heavyweight polypropylene mesh (90 g/m 2 ) is preferable.
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Operative Steps
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Planning Incision
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A generous midline laparotomy is typically performed.
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Elliptical incisions are used to incorporate previous scars, skin ulcerations, or defects.
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Patients should be counseled that often the umbilicus becomes devascularized and may likely require resection.
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The lower abdominal skin crease should be marked so as to avoid placing the incision through this fold. This area often becomes macerated postoperatively and can result in skin breakdown. In most patients, the pelvis can be fully exposed without extending the incision all the way to the pubis. Likewise, if the patient has a large pannus, extending the incision into the pannus should be avoided unless absolutely necessary.
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I prefer not to perform a simultaneous panniculectomy, particularly if the hernia defect is large and complex. Although the panniculectomy provides early improved cosmesis, it is associated with a much higher risk of wound morbidity and potential mesh infection. If patients have significant excess skin, it can be removed in a vertical fashion. A true panniculectomy can be performed in the future after the entire mesh repair has healed.
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Lysis of Adhesions and Removal of Old Mesh
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Complete lysis of all visceral adhesions to the anterior abdominal and pelvic walls is performed. Lysis is particularly important in cases in which dissection is planned in the abdominal wall lateral to the linea semilunaris.
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For the abdominal wall to be completely medialized, it must first be freed from the intestinal block. I typically perform a complete intra-abdominal adhesiolysis. Although it is not mandatory, I believe that with the large mesh placed in the retrorectus position, any bowel issue is best identified and addressed at this operation.
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During adhesiolysis, it is important to avoid damage or resection of the peritoneum and posterior rectus sheath. The typical adage of staying a layer superficial in the abdominal wall during adhesiolysis is not appropriate in this situation. If the surgeon resects a large portion of the peritoneum, particularly in the lateral abdominal wall, the retrorectus and preperitoneal space often cannot be recreated.
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The surgeon must also avoid entering into the retroperitoneum around the pericolic gutters. It is easy to get deep to the white line of Toldt during adhesiolysis and separate the colon from the retroperitoneum. If this occurs when the surgeon is entering into the preperitoneal plane as he or she advances laterally, he or she will have dissociated the peritoneum from the retroperitoneum, which can require aborting the posterior component separation procedure.
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I typically remove all prior synthetic or biologic mesh. Because mesh never grows into mesh, it is important to place the new mesh next to healthy well-vascularized tissue. Great care should be taken when excising intraperitoneal mesh to avoid resecting the peritoneum and posterior rectus sheath. In my experience, polytetrafluoroethylene and polypropylene mesh can often be removed without damage to the underlying peritoneum; however, polyester mesh often integrates into the peritoneum and can result in major defects if resected.
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Before removing any laparoscopically placed mesh, it is helpful to remove all tacks and transfascial sutures, as these often are the main points of fixation past the peritoneum.
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After the adhesiolysis is completed and gastrointestinal surgery is performed, attention is then turned to the abdominal wall. I place a large countable towel over the entire viscera from pelvic gutter to pelvic gutter ( Fig. 5.2 ). The towel helps avoid inadvertent injuries to the viscera, particularly during lateral dissection along the peritoneum during the transversus abdominis release, as this layer can be very thin.
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