Chapter 62: Abdominal Wall Reconstruction

wall? The anterior abdominal wall comprises a myofascial complex consisting of five paired muscles and a number of key fascial layers and interfaces enveloping them. The five key muscles are the rectus abdominus, external and internal oblique, transversus abdominis, and pyramidalis. Each has an important functional role with the exception of the pyramidalis. The two rectus abdominis or “six pack” muscles are para-midline paired muscles that run from the pubic ramus to the xiphisternum and ribs five through seven. They are enclosed by fascia anteriorly and posteriorly that joins in the midline as the linea alba or “white line” (not the linea semilunaris which represents the lateral fascial adherence of these muscles). The composition of this fascial arrangement, which includes anterior and posterior components, differs above and below the arcuate line, which is a sheath comprises the external oblique aponeurosis and the anterior leaf of the internal oblique aponeurosis throughout its length. Above the arcuate line, the posterior leaf of the internal oblique aponeurosis forms the posterior sheath, along with the transversus abdominis and transversalis fascia. Below the arcuate line, the posterior sheath consists of only transversalis fascia, and everything else is anterior to the rectus abdominis and contained within the anterior sheath. This is why patients are at increased risk of developing iatrogenic hernias of the lower abdomen following laparotomy or free transverse rectus abdominis myocutaneous (TRAM) harvest when the anterior fascia is deficient.1 The lateral border of the anterior abdominal wall is the midaxillary line (not the anterior axillary line). The superior border is the xiphisternum and the seventh to twelfth costal cartilages. The inferior border is the pubic tubercle and inguinal ligament. The paired pyramidalis muscles are small triangular structures sited between the rectus abdominis and the posterior surface of the rectus sheath. They are functionally unimportant and often absent. It has been postulated that they serve to tense the linea alba.1–3

2. Lovering RM, Anderson LD. Architecture and fiber type of the pyramidalis muscle. Anat Sci Int 2008;83(4):294–297

3. Khansa I, Janis JE. Modern reconstructive techniques for abdominal wall defects after oncologic resection. J Surg Oncol 2015;111(5):587–598 VASCULAR ANATOMY OF THE ANTERIOR ABDOMINAL WALL 2. When considering the vascular anatomy of the anterior abdominal wall, which one of the following is true? Knowledge of the blood supply to the anterior lower abdomen is vital to free tissue harvest from the abdomen and abdominal wall reconstruction. The vasculature has been classified by Huger into three zones: a central midline zone (zone I) which overlies the rectus muscles, an inferolateral zone (zone II) which overlaps zone I and continues laterally toward the anterior superior iliac crests and paired groin creases, and a superolateral zone (zone III) which lies above zone II and lateral to zone I. Zone I is supplied by the superior and inferior epigastric vessels (not just superior), which collateralize in the middle third of the rectus muscle near the umbilicus. It is in this area that most perforators are found. The deep inferior epigastric vessels provide the dominant blood supply and usually have medial and lateral perforator rows, of which the medial (not lateral) is usually dominant and allows perfusion of a greater amount of the contralateral hemiabdomen. These perforators are utilized in free tissue harvest of the anterior abdominal wall and are preserved in minimally invasive component separation procedures. Zone II does share blood supply from zone I with input from the deep inferior epigastric vessels, but also receives blood from other branches of the common femoral artery, namely, the superficial circumflex femoral artery, superficial inferior epigastric artery, and external pudendal artery. Zone III has a robust blood supply which is why the entire abdominal wall remains viable after abdominoplasty, component separation, or double deep inferior epigastric perforator (DIEP) harvest as thoracic intercostal and lumbar perforators contribute to its vascularity (Fig. 62.1).1,2

The revised ventral hernia classification system proposed by Kanters et al1 followed a review of a group of 299 patients who had undergone ventral wall hernia repair. The study was undertaken to evaluate the accuracy of the original classification by the Ventral Hernia Working Group (VHWG)2 in predicting surgical site occurrence after open ventral hernia repair. Following the study, the authors concluded that modification of the original Fig. 62.1 Huger zones. Zone I Deep superior epigastric artery Eleventh posterior intercostal artery Superficial circumflex femoral artery Superficial inferior epigastric artery Deep inferior epigastric artery Femoral artery External pudendal artery Zone III Zone II VHWG classification system to three grades, instead of four, with redistribution of patients from the original grades, significantly improves the accuracy of predicting surgical site occurrence.1 Using the revised system, patients are stratified according to their comorbidities, their prior history of wound infection, and their Centers for Disease Control and Prevention (CDC) wound contamination status. The Kanters classification is currently the only formally validated system for ventral hernia repair. The grade of abdominal wall hernia using this system helps guide the nature of the surgical repair.1,2

Principles in repair of abdominal wall hernias include patient optimization, preparation of the wound, and appropriate surgical techniques. Blood sugar levels should be less than 110 mg/dL and elective surgery should be postponed if HBA1C is greater than 7.5. Smoking cessation must be complete at least 4 weeks before surgery (not 4 months) to optimize postoperative healing. Furthermore, patients must be able to maintain cessation through the postoperative healing phase as smoking has been shown to affect many elements of patient outcomes including wound healing and chest complications, not just only in abdominal wall reconstruction.1–4 The wound must be adequately debrided and may require serial procedures before reconstruction. However, the two procedures do not always need to be staged. Repairs should always be reinforced and this fact is supported by level A evidence. The repair material will differ according to the grade of ventral wall hernia. Nonabsorbable mesh is preferred in low-risk repairs. Fistulas must be adequately addressed prior to reconstruction, but these sites still need reinforcement.4,5

formation in the longer term. Polyglycolic acid and polyglactin 910 are both absorbable materials that can be used as temporary mesh supports in abdominal wall reconstruction. They are not suitable for repairs of areas deficient in fascia, because their lack of permanence can result in hernia formation in the long term. Nonabsorbable polypropylene mesh, such as Marlex, is durable and strong with good resistance to bacterial contamination. Gore-Tex sheet is produced with ePTFE, but its use is limited because it does not allow fluid egress or fibrous ingrowth. Tissue expanders can be placed between the internal and external oblique muscles and in the subcutaneous plane. AlloDerm is acellular human cadaver dermis and is not available in the United Kingdom. Furthermore, it tends to stretch over time and may be insufficient to prevent bulging and herniation. Instead, a porcine acellular dermal matrix, which is less prone to stretching and has comparable strength to fascia lata, can be used in many countries.1–6

There are a number of newer composite prosthetics that combine both absorbable and nonabsorbable materials such as polypropylene and polyglactin, or nonabsorbable and tissue-separating barrier materials such as polypropylene and cellulose. Proceed and Supramesh are examples of the latter type and should help maintain tissue separation and adhesion formation. The benefits of materials such as Vypro and Ultrapro, which contain a combination of absorbable and nonabsorbable alloplastic materials, are that handling and initial strength may be improved while reducing the amount of foreign body present in the longer term. None of these materials contain purely absorbable material and will not resorb completely, and tissue integration differs between materials, but will never match that of normal tissue. A caveat with these materials is that they tend to be more expensive than traditional prosthetics. Although these newer materials should reduce bowel adhesions, it is still advisable to cover the bowel with omentum to separate the bowel from the mesh.1–3

There are a variety of acellular dermal matrices (ADMs) in use. They are either bovine, porcine, or human in origin. They are expensive compared with alloplastic materials and their use should be targeted to contaminated wounds in which prosthetic mesh must be avoided. Permacol is an example of a crosslinked porcine ADM. Cross-linking will help to control enzymatic degradation of the graft, but it tends to make the product behave more like a synthetic with less tissue integration. A vast majority of ADMs such as Surgimend, AlloDerm, XenMatrix, and Strattice are not crosslinked. Hernia recurrence rates are highly variable when using ADMs1 and the highest rates are when used as a bridging technique. A major benefit of their use is that they produce few visceral adhesions compared with prosthetics and may be placed directly onto the bowel. Their use is however off-label from an Food and Drug Administration (FDA) perspective.

repair? The placement of mesh in the abdominal wall is generally required for abdominal wall hernia reconstruction. The position of this mesh will depend on a number of factors according to the defect and associated soft tissues. In principle, the best place for the mesh is away from the intra-abdominal contents and yet with sufficient vascularized soft tissue cover to protect it from the external environment. Accordingly, the ideal position is probably retrorectus as there is no contact with either the external environment nor the intra-abdominal contents. Furthermore, the rectus muscle should be well vascularized to help with healing and tissue integration. From a biomechanical perspective, mesh placed internally to a fascial layer, that is, an inlay mesh, will be preferable as when intra-abdominal pressure increases the mesh will be forced close to the native fascial layer and close the repair gap. This will apply to deeper placement beneath any one of the deep fascial layers. In contrast, an onlay mesh placed suprafascially will tend to be forced away from the fascial attachment with increased abdominal pressure. Interpositional bridges represent the weakest repair biomechanically as their strength has no additional fascial support. For this reason, they are associated with the highest rate of recurrence and bulge. Where meshes must be placed intraperitoneally, it is best if they can be placed flat without bulges and on top of omentum to reduce adhesion and its subsequent complications. In all cases, where mesh is used, 3–5 cm of overlap between the material and fascia is advised.1–3

levels. In 1990, Ramirez et al1 published results of a clinical and anatomic study to determine whether separation of the components of the abdominal wall musculature allows increased mobilization of each to close large abdominal wall defects. They dissected 10 cadavers and found that the external and internal oblique muscles could be separated in a relatively avascular plane. This allowed medial advancement of the rectus (once elevated from the posterior sheath) as a composite with the internal oblique (not external oblique) and transversus abdominis muscles. The advancement was far greater than with direct closure of all components as a single composite. The neurovascular structures were identified between the internal oblique and transversus abdominis, and these two structures were tightly adherent to one another. To perform the procedure, the external oblique aponeurosis is split longitudinally at the linea alba. This plane is developed laterally between the external and internal oblique muscles to the midaxillary line. The posterior rectus sheath is also separated from the rectus via a midline incision to facilitate advancement. After their anatomic study, Ramirez et al performed the procedure in 11 clinical cases, which were also presented in the paper. Good clinical outcomes were observed in all cases. In four of the patients who had preoperative back pain, the problem resolved after surgery. Although Ramirez et al are quoted as having originally described the technique, the first description of this concept actually dates back to a paper by Young2 in 1961 for repair of epigastric hernias. The original description did not take a perforator-sparing approach. This has been subsequently described by a number of authors to decrease risk of dehiscence and seroma. This is achieved by using access tunnels or endoscopic approaches.3–5

Ramirez et al1 quoted the following figures for unilateral advancement: 5 cm at the epigastrium, 10 cm at the middle third, and 3 cm in the suprapubic region. These figures are doubled for the bilateral advancement. Although some surgeons report much greater advancement at the midabdomen, they also indicate that advancement of the upper and lower third are difficult to achieve without posterior sheath release or extension over the costal margins.

abdominis myocutaneous (TRAM) flap instead of the planned deep inferior epigastric perforator (DIEP) flap. A 5 When a planned DIEP flap requires conversion to a muscle-sparing TRAM flap, a residual fascial defect in the anterior rectus sheath warrants repair. If the defect is small (less than 2 cm wide), direct closure may be possible; otherwise, reinforced closure is required. Although the benefits of mesh over direct repair are debated, Luijendijk et al1 conducted a large study that showed significantly lower rates of incisional hernia recurrence where mesh repairs were used compared with direct suture repair only. Wan et al2 showed similar rates of hernia in patients after a TRAM flap with mesh repair compared with those who had a DIEP procedure. Without a mesh repair, the rates were higher in the TRAM group. Permanent mesh such as polypropylene is probably the best option for this clean, elective surgery. These products are inert, readily available, inexpensive, and provide good long-term strength and support. Inlay mesh repair is in theory biomechanically superior because the forces acting on it by intra-abdominal pressure will push the interface between mesh and abdominal wall firmly together at the areas of overlap. Debate exists over the benefits of underlay versus overlay techniques. However, the VHWG3 suggested the use of an underlay rather than an overlay in open procedures for abdominal wall repair. Polyglactin 910 is less appropriate, given that it is absorbable and cannot provide long-term support. Acellular dermal matrix has a role in abdominal wound closure, but the benefits in this situation do not support the increased cost. Component separation would not be required for a defect of this nature.

This patient has a number of options, including lifestyle modification or revision surgery. The former is unlikely to be acceptable to this patient given her age and lifestyle demands. A key principle in repair of this hernia is to reapproximate and centralize the rectus muscles and for this, a component separation should be used. The repair will also need reinforcement with a mesh. In this case a permanent mesh such as polypropylene would be a good choice, although there are other options too, as there is no ongoing infection and the bowel is not likely to be involved. A further option not listed is a Rives-Stoppa procedure. The Rives-Stoppa technique can be useful in patients with a large ventral hernia. It employs a reinforcing mesh sublay in the retromuscular space between the rectus muscle and the posterior rectus sheath, but it can be limited by the lateral edge of the posterior rectus sheath. Therefore, for larger defects, a larger inlay mesh is sometimes placed behind the rectus sheath but outside of the peritoneum.1–7