Updates in Abdominal Wall Reconstruction

A wide variety of surgical options exist for abdominal wall reconstruction. Part of the key to success, however, consist on choosing the operation that will give the most functional and aesthetic result while focusing on measures to decrease the incidence of catastrophic complications and need for reoperation. In this article, we review reconstructive modalities for abdominal wall defects, with special attention to complex ventral hernias and components separation techniques. Our description of recent scientific advances and the emphasis on a multidisciplinary approach to patient care reflects current trend and going forward to the use of bioprosthetic materials. Anaplastology An aplogy


Introduction
Revolutionary advances have been developed in the past 20 years with respect to abdominal wall reconstruction. Innovative Surgical approaches and new biological and prosthetic materials have become an integral part of the surgical arsenal. Patients with complex abdominal wall defects must be evaluated on an individual basis; interventions can vary from simple coverage and contouring to reconstruction of a dynamic functional abdominal wall. This article reviews abdominal wall reconstruction, with particular attention to ventral hernias, the components separation procedure, and use of bioprosthetic materials.

Abdominal Wall Embryology, Anatomy, and Function
The abdomen originates from the mesoderm of paravertebral region as bilateral sheets that migrate anteriorly and envelop the future abdominal [1]. Along with the rectus muscles, the external and internal oblique muscles and transverse muscles start to develop in the 6 th to 7 th week of gestation and their fascia encase the recuts abdominis muscles before these fuse in the midline. The leading edges of this sheet develop into the rectus abdominis muscles, which eventually meet in the midline anteriorly by week 12 th .
Superiorly the abdomen is bound by the costal margins, inferiorly by the symphysis pubis and pelvic bones, and posteriorly by the vertebral column. Anatomic layers superficial to deep include: the subcutaneous tissue, superficial fat layer (Camper's fascia), deep fat layer (Scarpa's fascia), external oblique, internal oblique and transversus abdomini muscles, preperitoneal fat layer and peritoneum.
The anterior and lateral abdominal wall comprises a set of four paired muscles: the rectus abdominis, the external oblique, the internal oblique, and the transversus abdominis muscles. They are involved in the most obvious functions of the trunk: flexion, extension and rotation of the trunk and the pelvis; increase the intra-abdominal pressure for the aid of respiration, defecation, micturition, parturition and mechanisms of the inguinal canal and protect abdominal and retroperitoneal structures.
Rectus abdominis muscle fibers are arranged vertically and are encased within anterior and posterior leaves of an aponeurotic sheath, which are fused in the midline to form the linea alba. The rectus abdominis inserts on the symphysis and pubis crest inferiorly, and superiorly on the anteroinferior aspects of the fifth and sixth ribs and the seventh costal cartilages and the xiphoid process. The lateral border of the rectus muscles assumes a convex shape that gives rise to the linea semilunaris.
The external oblique muscle is the most superficial and largest of the anterolateral aspect of the abdominal wall. It originates in the lower eight ribs where it interdigitates with the serratus anterior and latissimus dorsi muscles; its fascicles originate superolaterally and are directed inferomedially inserting on the anterior half of the iliac crest. At its inferior-most aspect, the external oblique aponeurosis reflects posteriorly in between the anterosuperior iliac spine and pubic tubercule forming the inguinal ligament. Its aponeurosis passes anterior to the rectus abdominis muscle.
The internal oblique muscle lies immediately deep to the external oblique muscle and arises from the lateral aspect of the inguinal ligament, the iliac crest, and the thoracolumbar fascia. Its aponeurosis splits above the arcuate line to envelope the rectus abdominis. Below the arcuate line it passes anterior to the rectus abdominis. The lower fibers join those of the transverse abdominis muscle to form the conjoined tendon, which inserts on the pubic crest and spine and on the iliopectineal line. The inferior-most fibers of the internal oblique muscle are contiguous with the cremasteric muscle in the inguinal canal.
The transversus abdominis muscle is located deep in the internal oblique muscle. It is the deepest and smallest of the muscles of the lateral abdominal wall. It originates from the lower six ribs, lumbodorsal fascia, anterior two thirds of the iliac crest, and lateral third of the inguinal ligament. It inserts on the linea alba, contributes to the conjoined tendon, and inserts on the pubic spine and iliopectineal line.
The pyramidalis muscle is present in 80% to 90% of patients. It is a small triangular muscle that lies superficial to the rectus muscle. It arises from the front of the pubis and inserts on the linea alba halfway between the symphysis and umbilicus.
The blood supply to the abdominal wall is better described in relation to the area that is irrigated as described by Huger et al. [2] ( Table 1).

Abdominal Wall Defects
Abdominal wall defects may be congenital or acquired. This review focuses on the latter. Often, such defects manifest themselves as massive ventral hernias and result from prior abdominal operations, trauma or edema related loss of domain, massive infection, radiation necrosis, or tumor resection.
Prevention of evisceration, creation of a tension free abdominal wall repair with dynamic muscle support and stable soft tissue coverage are the goals of abdominal wall reconstruction.
Decisions regarding technique are based on an assessment of the overall clinical status of the patient, the location and size of the defect and well as extension of layers involved, and etiology.
Open primary tissue closure, open or laparoscopic prosthetic mesh placement, local advancement or regional flaps including the components separation technique, distant flaps, and combined flap and mesh techniques are the surgical approaches currently used. The choice of one approach over the other varies on a case-by-case basis as well as surgeon preference.

Ventral Hernias
The incidence of ventral hernias as a complication of abdominal operations has been reported as high as 20% [3].
Several conditions contribute to the development of incisional hernias such as: suture type, repair technique and tension, poor wound healing (often associated with poor patient nutrition), infection, increased intrabdominal pressure (e.g. due to COPD), and metabolic connective tissue disorder [4].
The most common indications for repair of abdominal wall hernias are generalized pain (68.7%) and cosmesis (54.6%). Other indications include the concern with risk of incarceration or strangulation and a massive or enlarging hernia.
Open techniques may range from simple herniorraphy, fascial plication, components separation, and mesh placement as an underlay, retrorectus or overlay.

Component Separation Techniques
Donald Young first described the release of the external oblique in 1960 [5]. Thirty years later, Ramirez et al. introduced the components separation technique (CST) which involved the release of the posterior rectus sheath in addition to the external oblique fascia [6]. This method uses bilateral, innervated, bipedicle, muscle flaps advanced medially to reconstruct the central abdominal wall defects. The components separation technique represents a landmark for the tissue transfer techniques used to repair complex abdominal midline defects [7].
The technique as described first exposes the anterior sheath of the rectus abdominis muscle and the aponeurosis of the external oblique muscle and the intervening linea semilunaris. The external oblique aponeurosis is longitudinally transected lateral to the rectus sheath in a line extending from the costal margin to the pubis. The plane between the external oblique muscle and the internal oblique muscle is developed and the dissection is carried out laterally as far as possible. If needed, the posterior rectus sheath is also incised longitudinally, particularly beneficial in retrorectus placement of mesh ( Figure 1). The fascia may be closed at the linea alba with a running or interrupted absorbable or non-absorbable suture [6,8].
Ideal candidates are those who have no pre-existing flank hernia, no prior injury to deeper fascial layers and existing rectus abdominis muscles.
In the first randomized control trial comparing wound complication and recurrence rates of intraperitoneal prosthetic mesh repair versus component separation technique, de Vries Reilingh et al., reported similar recurrence rates, hematoma, seroma and skin necrosis [9]. No superior results were reported for the mesh group in regards to wound infection requiring reoperation. However, less catastrophic complications, such as fistula formation, were reported in the CST group ( Figure 2).
It is thought that such wound complications carried by CST are related to the division of rectus muscle perforator arteries that supply the overlying skin in the creation of the skin flap to find the Zones Territory Supply I Midcentral abdominal wall above the umbilicus.

II
Lower abdominal wall below umbilicus.

III
Lateral abdominal wall. Intercostal, subcostal, and lumbar arteries.    linea semilunaris. Therefore improvement of the blood supply to the abdominal skin flaps is fundamental to primary midline wound healing [10] and only those perforators that are absolutely necessary for exposure are ligated.
Subsequently, Saulis and Dumanian described a technique that preserved the periumbilical rectus abdominis perforators to the overlying skin flaps. In their retrospective review they observed a decreased in overall wound complications to 7% when compared to the 31% of the conventional approach [11].
Endoscopic separation of components has been described, where, based on the same concept of preserving the perforators, the external oblique aponeurosis is released with the aid of an endoscope and balloon dissector via small separate anterolateral cut down incisions [12].
Supplemental mesh placement is under the discretion of the surgeon, however in another study by Dumanian primary components separation (n=158) yielded a 22.8% recurrence rate. Closure of the midline tissues with augmentation of the repair using acellular dermis underlay (n=18) had 0% recurrence (p=0.04) [13].
More recently, further modification of perforator sparing concept on CST has been described for patients with complex and large defects as well: The minimally invasive component separation technique with inlay bioprosthetic mesh [14]. In this interesting repair, the external oblique is released via the same midline incision after being exposed and incised through a limited skin flap over the rectus. Using a suction head, the external oblique is elevated from the internal oblique and then incision is extended caudally and cranially via that limited window. The repair was described with a placement of inlay bioprosthetic mesh. A retrospective comparison of this technique compared with the conventional CST resulted in fewer wound related complications (14% over 32%) and similar recurrence rate. However this review has its flaws such as longer follow up time in the CST group and potential selection bias [14].

Mesh
The primary choice of repair of these hernias whether open or laparoscopic with or without mesh is a topic of debate, however most surgeons believe prosthetic mesh repair is the standard of care for the non complex hernia patient with a fascial defect greater than 2 cm.
There are a limited number of randomized control trials that support the use of prosthetic mesh over primary repair. The literature suggests that prosthetic mesh repair has been associated with less recurrence rates but with higher incidences of wound infection when compared to primary repair for non complex hernias with defects sizing 6 cm or less [8,15]. Moreover, there is no evidence which type of mesh is superior for the repair [8]. Types of mesh are covered below.
Prosthetic material is commonly used for structural support of the abdominal wall or as a bridge to definite treatment in a planned open abdomen or in light of an infected wound. The use of prosthetic material is relatively contraindicated in cases of wound infection. Also, the inability to interpose omentum between mesh and bowel also makes the use of prosthetic mesh unfavorable [9].
Ideally, this prosthetic material should meet certain criteria prior to its use. They should be resistant to mechanical forces and durable. As any other foreign materials to be utilized in the body, it should be chemically inert in order to reduce inflammatory response and be capable of host tissue incorporation. It should also be shapeable.
The two most commonly used prosthetic materials are polypropylene and expanded polytetrafluoroethylene (ePTFE).
Expanded polytetrafluoroethylene (Gore-Tex, W.L. Gore and Associates, Flagstaff, Arizona) has a microporous structure that minimizes cellular infiltration and tissue incorporation. It is equivalent to polypropylene in terms of suture retention strength. As a result of its flexibility, conforming nature, and minimal tissue ingrowth, ePTFE can be placed directly on bowel. The material is virtually impenetrable, preventing host tissue ingrowth and often leading to seroma formation.
Synthetic mesh offers high tensile strength, however it is associated with chronic inflammatory response and scar formation that subsequently promotes visceral tissue ingrowth into mesh porosities that can lead to complications such as adhesions to the mesh, bowel obstruction, and enterocutaneous fistula [16].
Therefore in clinical situations such as acute repair of incarcerated hernias with spillage of enteric contents, or mesh infections prosthetic mesh use is not advised [14,16].
Dual characteristic with absorbable and nonabsorbable prosthesis have been developed in order to reduce the above mentioned prosthesis related complications, however there is no enough data to support their use over the traditional ones.
In the past decade, the use of acelullar dermal matrix for soft tissue reinforcement has been popularized for the use of abdominal wall reconstruction as a substitute for flaps, failed prosthetic repair and complex hernias where prosthesis is not advised. These products consist of human (allograft) and animal (xenograft) products in the form of acellular dermal matrix and submucosa [16].
Among bioprosthesis characteristics are resistance to infection, biocompatibility to human tissue, tolerance to cutaneous exposure, and mechanical stability. Furthermore these products have less potential for bowel adherence and infection development and are ideal alternatives to prosthetic mesh implants in recurrent or complicated repairs. For such reasons they have become a popular and reliable option for hernia repair over the recent years ( Figure 3). Due to lack of larger comparative trials there is no evidence that one mesh is better than the other [16].
These products consist of an acellular collagen matrix that promotes host tissue remodeling while maintaining mechanical integrity. They differ in that they heal by a regenerative process rather than by scar tissue formation. Disadvantages are their high cost and the lack of longterm follow-up studies validating their use.
Xenografts have larger and thicker available sizes and the favorable viscoelastic properties in these products and the trend has shifted to use products for abdominal wall reconstruction in lieu of allografts [16]. Moreover, abdominal wall reconstructions with allograft have been found to have a very unacceptable degree of bulging and recurrence at long term as compared with the ones where prosthetic mesh is used [17,18].

Types of Flaps
The rectus femoris is a large and reliable flap with consistent anatomy and a broad arc of rotation. It is ideal for low anterior pelvic reconstruction when other options are not feasible. When pedicled, there is no need for microvascular anastomosis as this flap has a robust blood supply [20]. Donor site has minimal morbidity.
Extended rectus femoris myocutaneous flap (the mutton chop flap) allows for reconstruction of large full-thickness epigastric abdominal wall defects as described initially, or the entire sacral and perineal area, without prosthetic material [21,22].
The tensor fascia lata (TFL) has been extensively described for not only is an ideal reconstructive option for abdominal wall defects that can also be used as musculocutaneus flap. The flap can be used to resurface the entire suprapubic region, lower abdominal quadrants, or ipsilateral abdomen with minimal donor deficit. Donor site from narrow flaps can be closed primarily; larger than 8 cm may need skin grafting (Figure 4). The transverse branch of the lateral femoral circumflex vessels arising from the profunda femoris, pierces the medial aspect of the flap 8 to 10 cm below the anterosuperior iliac spine as the vascular pedicle.
The omentum can also be used as a flap to cover the entire abdominal wall and perineal areas. It can be used with mesh and provides a good bed for a skin graft.

Contouring Procedures in Combination with Hernia Repair
More often than not larger ventral hernias cause the overabundance of or sagging overlying skin, stretch marks, scar and on extremes cases necrosis. Abdominal wall contouring procedures can be performed additionally at the time of the hernia repair, as the goal is to restore an aesthetic shape to the wall.