Anterior abdominal wall and inguinal region

Part 1: Anterior abdominal wall

Duncan SG Scrimgeour, Matthew J Laviolette, Sam M Wiseman

Core Procedures

Laparotomy

Vertical, transverse and oblique incisions
Ventral incisional hernia repair
Umbilical hernia repair
Spigelian hernia repair
Epigastric hernia repair
Abdominal wall closure

Laparoscopy

Hasson's open technique
Modified Hasson's technique
Veress needle technique
Optical trocar technique

Other

Component separation
Transversus abdominis plane (TAP) block

Despite the significant advances that have occurred in minimally invasive surgery over the past several decades, an understanding of the anatomy of the anterior abdominal wall has remained of critical importance to surgeons because it forms the basis not only for the creation and closure of abdominal wall incisions, but also for hernia repair.

Embryology and congenital anomalies

The anterior body wall is formed by ectodermal epithelium, which becomes the epidermis of the skin, and the underlying somatopleuric mesenchyme, which differentiates into (from superficial to deep) the tissues within the dermis, the layers of connective tissues that form the aponeuroses of the anterior abdominal wall musculature, and the lamina propria of the parietal peritoneum. Muscles of the anterior abdominal wall arise from extension of the somite dermomyotomes into the lateral and ventral body walls. This hypaxial population gives rise to a premuscle mass, which, through interaction with local somatopleuric mesenchyme, splits into the muscle populations for the oblique muscles, transversus abdominis and rectus abdominis. The right and left recti approximate and become fused, except at the umbilical ring.

An overview of the development of the gastrointestinal tract is reviewed in Chapter 66 . During stages 15–22 (35–55 days post fertilization) of embryonic development, the midgut increases in length and moves into the extraembryonic coelom within the forming umbilical cord. The midgut returns to the abdominal cavity from the tenth week post fertilization. As it does, the structures that pass within the fetal umbilical cord to the body may be distinguished: cranially, a single (left) umbilical vein that passes from the umbilicus to the liver within the falciform ligament; and caudally, within the connecting stalk mesenchyme, the allantois and its fibrous remnant, the urachus (continuous with the urinary bladder), and two umbilical arteries, which are branches of the internal iliac arteries. Vestiges of the caudal structures remain as the (single) median and (bilateral) medial umbilical ligaments, respectively.

The vitelline duct, which connects the midgut to the involuting yolk sac, is covered by extraembryonic splanchnopleuric epithelium that is continuous with the visceral peritoneum. It is surrounded by the extracoelomic space, and is bounded by extraembryonic somatopleuric epithelium that is continuous with the parietal peritoneum. All of these structures and layers contribute to the umbilical cord, which has an outer covering of amniotic membrane. Failure of midgut reduction and subsequent closure lead to herniation of intra-abdominal structures through the umbilical ring and into the base of the umbilical cord (omphalocele). Gastroschisis is a relatively common congenital abdominal wall anomaly that results from the herniation of intra-abdominal structures through a developmental defect of the abdominal wall musculature, usually to the right of the umbilicus. As is the case for an omphalocele, the abdominal cavity is generally too small to accommodate the intestines, leading to abdominal wall rupture and intestinal evisceration. With gastroschisis there is no hernial sac present, and the herniated bowel is usually covered by a gelatinous exudate, distinguishing it from an omphalocele, which is usually covered by an external amniotic layer and an internal peritoneal layer.

Surgical anatomy and approaches

The anterior abdominal wall is a hexagonal area bounded inferiorly by the inguinal ligament and the pelvic bones, and laterally by the mid-axillary line. Its superior boundaries are the cartilages of the seventh to tenth ribs, and the xiphoid process of the sternum. It consists of one paired longitudinal muscle, rectus abdominis, and three paired anterolateral muscles (external and internal obliques and transversus abdominis). These three paired flat muscles and their aponeuroses contribute to the rectus sheath before fusing in the midline to form the linea alba. The anatomy of the anterior abdominal wall may be reviewed in the context of the anterolateral region and the middle region.

Fasciae of the anterolateral abdominal wall

The superficial fascia is external to the muscles of the anterolateral abdominal wall. In the lower abdomen, it forms a superficial fatty layer (Camper's fascia), and a deeper membranous layer (Scarpa's fascia) that continues inferiorly into the perineal region as the superficial perineal fascia (Colles’ fascia). Scarpa's fascia is particularly well defined in children and may be mistaken for the external oblique aponeurosis. The transversalis fascia is a thin but firm layer of connective tissue that covers most of the abdominal wall, located between the deep surface of transversus abdominis and a variable amount of extraperitoneal fat. In the male, it continues at the inguinal canal as the internal spermatic fascia, enveloping the structures that pass through the deep inguinal ring.

Muscles and aponeuroses of the anterolateral abdominal wall

When choosing between muscle-splitting and muscle-transecting incisions, in order to avoid injuring the anterior abdominal wall musculature and to ensure the best possible postoperative outcome, it is important to understand the relationship of the muscles to their aponeurosis and to recognize the specific directions travelled by the muscle fibres, and the position and orientation of their associated neurovascular bundles. External oblique fibres pass inferomedially, travelling from the fifth to twelfth ribs to the outer lip of the anterior half of the iliac crest ( Fig. 55.1 ). An aponeurotic line, formed by the muscle fibres of external oblique, passes vertically inferiorly from the ninth costal cartilage to form the linea semilunaris, located at the lateral margin of the anterior rectus sheath (see Fig. 55.1 ). Herniation through the linea semilunaris is referred to as a Spigelian hernia , and most frequently occurs inferior to the level of the umbilicus along the semicircular arcuate line (line of Douglas) ( Fig. 55.2 ). Spigelian hernia repair usually employs mesh and may be performed laparoscopically. The arcuate line is located between the umbilicus and pubic crest. Below this line, all aponeurotic layers are reflected anterior to rectus abdominis, creating an area of potential weakness, where aponeurotic fibres from transversus abdominis fuse with those from internal oblique. At the anterior superior iliac spine (ASIS), the medial half of the aponeurosis of external oblique rolls on itself, between the ASIS and the pubic tubercle, forming the inguinal ligament. It is entirely aponeurotic inferior to the level of the ASIS. The external oblique is covered by a thin fascial layer, the external oblique fascia (innominate fascia of Gallaudet), which also continues along the spermatic cord and forms the external spermatic fascia. Internal oblique is located deep to the thicker and bulkier external oblique; its muscle fibres fan out anteromedially from the thoracolumbar fascia and the iliac crest to insert on the lowest three to four ribs ( Fig. 55.3 ). The origin of the lowermost fibres of internal oblique remains controversial: many investigators now believe that these fibres, traditionally believed to arise from the lateral two-thirds of the inguinal ligament, arise from the iliopsoas fascia. None the less, at this level, the muscle fibres of internal oblique run perpendicular to those of external oblique, a distinction that assists their identification intraoperatively. The aponeurosis of internal oblique, which is formed at approximately the same level as that of external oblique, fuses with the corresponding aponeurosis of transversus abdominis to form the conjoint tendon (inguinal aponeurotic falx) (see Figs 55.14 and 55.18 ). As its name suggests, most of the fibres of transversus abdominis run transversely; its lowermost fibres travel obliquely and inferiorly (see Fig. 55.2 ). Transversus abdominis arises from the inner surface of the lower six costal cartilages, the thoracolumbar and iliopsoas fasciae, and the iliac crest. The uppermost fibres of transversus abdominis interdigitate with the diaphragm and its aponeurosis passes medially and fuses with the linea alba. The lower aponeurosis joins the aponeurosis of internal oblique and is inserted into the pubic crest and pectineal line to form the conjoint tendon.

Fig. 55.1, The left anterolateral abdominal wall muscles.

Fig. 55.2, The left transversus abdominis. The aponeurosis of transversus abdominis fuses into the posterior layer of the rectus sheath above the arcuate line. The position of the lateral border of rectus abdominis is shown by the dashed white line.

Fig. 55.3, Muscles from the left side of the trunk. External oblique has been removed to show internal oblique but its digitations from the ribs have been preserved. The sheath of rectus abdominis has been opened and its anterior layer removed.

Muscles of the middle abdominal wall

Rectus abdominis is a long, broad, strap-like muscle that runs vertically down the entire length of the anterior abdominal wall on either side of the midline (see Fig. 55.3 and ). Superiorly, it is attached to the fifth, sixth and seventh costal cartilages and the xiphoid process; inferiorly, it is attached to the pubic crest, ligamentous tissue at the pubic symphysis, and the superior ramus of the pubis. Each rectus abdominis is bounded by the linea alba medially and by the linea semilunaris laterally. The muscle is wider and thinner superiorly, and thicker and narrower inferiorly. It is attached to the anterior rectus sheath by three or four fibrous bands (tendinous intersections or inscriptions) that pass transversely across the muscle at the xiphoid and umbilicus, and midway between these two points. These bands must be transected in order to detach the anterior rectus sheath from rectus abdominis when making certain transverse abdominal incisions, such as the Pfannenstiel incision. There are no attachments between rectus abdominis and the posterior rectus sheath. Pyramidalis is a small triangular muscle that has been reported to be absent in 10–70% of the population on either one or both sides. When present, it lies anterior to the inferior portion of rectus abdominis and within the rectus sheath. It arises from the linea alba approximately midway between the umbilicus and pubis, and is attached to the pubis and anterior ligamentous fibres of the pubic symphysis. Pyramidalis must be divided when making a lower midline laparotomy incision because the linea alba lies posteriorly.

Rectus sheath, linea alba and umbilicus

The rectus sheath is of considerable importance because most abdominal incisions divide this strong fibrous structure. Surgeons must be very familiar with the anatomy of the rectus sheath during operations in order to avoid incisional dehiscence and hernia development after abdominal closure. The sheath consists of anterior and posterior layers that envelop rectus abdominis and pyramidalis ( Fig. 55.4 ; see Figs 55.2 , 55.3 ). External oblique and the anterior part of the aponeurosis of internal oblique form the anterior rectus sheath, and the posterior part of the aponeuroses of internal oblique and transversus abdominis form the posterior rectus sheath. The rectus sheath is best described in three separate areas. Superior to the costal margin there is no posterior rectus sheath because the aponeuroses of internal oblique and transversus abdominis are absent. At this level, the anterior rectus sheath is formed by the aponeurosis of external oblique and the costal cartilages that are located posteriorly (see Fig. 55.4 ). The second area, where both the anterior and posterior rectus sheaths are present, runs between the costal margin and the arcuate line. The third area is inferior to the arcuate line, where all three aponeuroses (of external and internal oblique, and transversus abdominis) blend together, forming an anterior rectus sheath. Here, rectus abdominis lies directly anterior to the transversalis fascia, which is thickened at this level. When closing a midline laparotomy incision only the anterior rectus sheath above the costal margin and below the arcuate line requires closure. Between these levels, both the anterior and posterior rectus sheaths are present and both should be included in the midline abdominal closure.

Fig. 55.4, A transverse section through the anterior abdominal wall. A , Immediately above the umbilicus. B , Below the arcuate line. Note that the rectus is supported directly by the transversalis fascia below the arcuate line.

The linea alba is a white fibrotendinous raphe running vertically in the midline for the entire length of the anterior abdominal wall, extending from the xiphoid process to the pubic symphysis. It separates the two recti and is formed by the interlacing and decussating aponeurotic fibres of external and internal oblique and transversus abdominis. Weaknesses of the linea alba can lead to herniations of extraperitoneal fat or peritoneum and abdominal contents, frequently along the linea alba between the xiphoid process and the umbilicus (epigastric hernia). Gradual thinning and widening of the linea alba, along with laxity of the anterior abdominal wall musculature, lead to the development of a diastasis of the rectus abdominis muscles (DRAM). DRAM may commonly develop during pregnancy but may also occur in men and children, with premature infants being at the highest risk. DRAM itself poses no threat of incarceration or strangulation, and surgical repair is usually not warranted. Underlying the umbilicus is an area in the middle of the linea alba, referred to as the umbilical ring, through which the umbilical cord passes prenatally. It is a fibrous cicatrix that represents the area of fusion between the two medial umbilical ligaments (the obliterated umbilical arteries) and the median umbilical ligament (the partially obliterated remnant of the urachus). The round ligament of the liver/ligamentum teres hepatis (obliterated umbilical vein) traverses the umbilical ring, arising from its inferior margin, and passes superiorly within the falciform ligament. Variability in the attachments of these ligaments may predispose some individuals to the development of an umbilical hernia. True umbilical hernias are congenital defects in which a peritoneal sac protrudes through a patent umbilical ring; they are uncommon in adults but common in children, and most spontaneously resolve by 3 years of age. Acquired umbilical hernias in adults usually develop through the superior margin of the umbilical ring and are referred to as para-umbilical hernias. They often occur in obese adults and are at risk of incarceration and strangulation. Inferior to the umbilicus, the linea alba is thinner and much less well defined than it is superior to the umbilicus. This is why, when using an open technique to create a laparoscopic umbilical port site, the incision is placed either transumbilical or immediately inferior to the umbilicus, in a location where the abdominal wall is thinner and may be more easily accessed.

Transversalis fascia

The transversalis fascia is a layer of connective tissue between transversus abdominis and the peritoneum. Superiorly, it is continuous with the inferior diaphragmatic fascia; inferiorly, it is continuous with the iliac and pelvic fascia, with several thickenings in the inguinal and femoral areas; and posteriorly, it fuses with the anterior lamina of the thoracolumbar fascia (see Fig. 55.5 ).

Innervation, vascular supply and lymphatic drainage

The muscles and skin of the anterior abdominal wall are innervated by the thoraco-abdominal and subcostal nerves (derived from the ventral rami of the sixth to the twelfth intercostal nerves) and by the first lumbar nerve (iliohypogastric and ilioinguinal nerves) ( Fig. 55.5 ). These segmental nerves run in an inferomedial direction across the anterior abdominal wall within a neurovascular plane located between internal oblique and transversus abdominis, and are therefore vulnerable to injury when an abdominal wall incision is made. A transversus abdominis plane (TAP) block anaesthetizes these segmental nerves by injecting a long-acting local anaesthetic agent into this neurovascular plane. The block was first described as a landmark-guided technique that involved a single needle entry point within the triangle of Petit, which lies between the lower costal margin and the iliac crest, bounded anteriorly by external oblique, and posteriorly by latissimus dorsi (see Fig. 55.1 ). A blunt needle is inserted through the skin and advanced blindly through external and internal oblique. After entering the skin, the needle should be gently manoeuvred from side to side to ensure that it has not penetrated the abdominal wall musculature. The needle is then advanced and a double ‘pop’ signifies entry into the TAP, the site for injection of local anaesthetic; ultrasound-guided TAP blocks may be more accurate and reliable.

Fig. 55.5, The cutaneous branches of the lower intercostal and lumbar nerves. Portions of the muscles of the anterior abdominal wall have been removed, including most of the anterior layer of the rectus sheath and parts of rectus abdominis.

Huger separated the blood supply of the anterior abdominal wall into three anatomically distinct zones ( Fig. 55.6 ). Zone I is the upper anterior midline of the abdominal wall and is supplied by the superior and deep inferior epigastric blood vessels. Zone II is the anterior abdominal wall inferior to zone I and is supplied by four main blood vessels: the superficial epigastric, superficial external pudendal, inferior epigastric and superficial circumflex iliac arteries (see Fig. 79.3 ). The musculophrenic, lower intercostal, subcostal and lumbar arteries supply zone III, which lies lateral to the linea semilunaris and superior to zone II. The superior epigastric artery is one of the two terminal branches of the internal thoracic artery; it passes anterior to the upper part of transversus abdominis and enters the rectus sheath, where it descends posterior to rectus abdominis ( Fig. 55.7 ). The deep inferior epigastric artery originates from the medial aspect of the external iliac artery immediately superior to the inguinal ligament. It penetrates the transversalis fascia, enters the rectus sheath either at or below the level of the arcuate line, and ascends between rectus abdominis and the posterior rectus sheath before anastomosing with the superior epigastric artery superior to the umbilicus (see Fig. 55.7 ). The major vessels of the anterior abdominal wall are usually located 4–8 cm from the midline; it is therefore recommended, whenever possible, to place trocars a minimum of 8 cm lateral to the midline (see Fig. 55.7 ; Table 55.1 ). The skin and subcutaneous tissue of the anterior abdominal wall drain into the internal thoracic veins medially, the lateral thoracic veins laterally, and the superficial and inferior epigastric veins inferiorly (see Fig. 55.7 ). The deeper veins accompany the arteries. Transillumination of the abdominal wall during laparoscopic port placement is a useful technique that can help the surgeon avoid injuring the abdominal wall blood vessels. The superficial lymphatic drainage of the anterior abdominal wall superior to the umbilicus is to the axillary lymph nodes, and to the superficial inguinal lymph nodes inferior to the umbilicus. Deep lymphatic drainage is to the lumbar and common and external iliac lymph nodes.

Fig. 55.6, The blood supply of the anterior abdominal wall separated by zones.

Fig. 55.7, The deep muscles and arterial supply of the anterolateral abdominal wall.

TABLE 55.1

Distances of superior and deep inferior epigastric arteries from midline

(Adapted from A.A. Saber, A.M. Meslemani, R. Davis, R. Pimentel, Safety zones for anterior abdominal wall entry during laparoscopy: a CT scan mapping of epigastric vessels, Ann. Surg. 239 (2004) 182–185, Table 2.)

Level	Left	Right
Xiphoid cartilage	4.5 ± 0.1 cm	4.4 ± 0.1 cm
Between xiphoid and umbilicus	5.4 ± 0.2 cm	5.5 ± 0.2 cm
Umbilicus	5.6 ± 0.1 cm	5.9 ± 0.1 cm
Between umbilicus and pubic symphysis	5.3 ± 0.1 cm	5.3 ± 0.1 cm
Pubic symphysis	7.5 ± 0.1 cm	7.5 ± 0.1 cm

Ventral incisional hernia repair

Ventral incisional hernias may be repaired using either an open or a minimally invasive surgical technique, or a combination of both. These repairs usually involve placement of a mesh product as an onlay, inlay, sublay or underlay ( Fig. 55.8 ). Open and laparoscopic approaches are well established in today's practice, and each has specific advantages and disadvantages. While there is a significant reduction in risk of incision and mesh infections with the laparoscopic approach, an inability to approximate the midline and allow for restoration of abdominal wall function is a disadvantage of this approach. Intracorporeal closure is easier to perform with robotic surgical techniques and may offer a solution to this problem, but long-term outcomes of such repairs are currently poorly defined. The laparoscopic approach lends itself well to the repair of moderately sized (2–6 cm) solitary hernia defects, or of smaller defects (less than 3 cm) in obese patients.

Though there is significant variability in laparoscopic hernia repair technique, some general principles must be considered. Once safe pneumoperitoneum has been established, the laparoscopic ports are inserted well away from the hernia defect, and adhesions are then divided. The hernia is reduced using atraumatic graspers and the fascial defect is measured intracorporeally before being closed with a non-absorbable suture. A 5 cm circumferential overlap of the fascial edges by mesh will reduce the risk of hernia recurrence, which may in part be due to mesh shrinkage. Intraperitoneal underlay meshes should have an adhesion prevention coating/barrier to reduce the risk of adhesion development and its associated complications, such as bowel obstruction or fistula. A wide variety of mesh products may be utilized for hernia repair, both synthetic (including polyester or polypropylene mesh, or an expanded polytetrafluoroethylene), biological and absorbable, or permanent composite meshes. The mesh is secured in place with transabdominal sutures, tacks or a combination of both.

During an open approach, the hernial sac is usually opened once it has been freed from the fascial edges and the contents of the sac are reduced back into the peritoneal cavity. This can be carried out through either a transverse or a vertical abdominal incision. The fascia can be closed over a sublay mesh; left open and repaired with an inlay (interposition) mesh; or closed and reinforced with an onlay mesh (see Fig. 55.8 ). Ideally, the mesh should overlap the defect edges by 3–4 cm circumferentially. Defects smaller than 4 cm have traditionally been repaired primarily with sutures but recent research suggests that mesh repair may even be beneficial for smaller umbilical hernias. Onlay repair is generally easier and quicker to perform than sublay mesh repair and is frequently utilized in the emergency setting, but has the disadvantage of an increased risk of hernia recurrence and seroma formation. Subcutaneous drains are usually utilized for these cases. Biological meshes are more commonly chosen if there has been contamination of the surgical field or if there is a significant risk of mesh exposure. For sublay repairs, the mesh is placed behind the rectus muscle and in front of the posterior rectus sheath (the Rives–Stoppa technique).

Surgical incisions and component separation

There are many considerations, beyond surgeon preference, that must be reviewed when deciding on the abdominal incision that will be created for a particular patient undergoing a specific operation, as part of the treatment of a certain problem. It is critical for the surgeon to anticipate the most likely diagnosis, as well as the potential complications that may occur as a consequence of the operation that is being performed. Other important considerations when creating abdominal incisions include an awareness of the challenges presented by the patient's body habitus and prior abdominal surgical history, and an appreciation of how quickly the abdominal cavity must be accessed. Maingot has described the three essential elements that should be considered before creating an abdominal incision as accessibility, extensibility and security. The incision should provide adequate exposure with minimal damage to abdominal wall muscles and their associated nerve supply, and allow for the best possible cosmesis. Access to the abdominal cavity may be accomplished via one of many different incision types, several of which are uncommonly employed in surgical practice today. In general, incisions may be classified as vertical, transverse, oblique or thoraco-abdominal ( Fig. 55.9 ).

Vertical incisions

Midline incision

The entire abdominal cavity and retroperitoneum may be readily accessed through a midline incision, which is the ‘work horse’ incision most commonly utilized by surgeons today. Midline incisions are quick to perform, avoid major nerves, are located in a relatively avascular site, allow for access to both the upper and lower abdominal organs, and may easily be extended. However, they are more painful than transverse incisions, their closure may more commonly require concurrent repair of a pre-existing hernia(s), and they may have a worse cosmetic appearance because they traverse Langer's lines.

As its name implies, a midline incision is carried out precisely in the abdominal midline. The skin, subcutaneous fat, linea alba, transversalis fascia, extraperitoneal fat and parietal peritoneum are each systematically and carefully divided. Symmetrical lateral digital traction on the incision edges may facilitate separation of the subcutaneous fat in the correct midline axial plane for exposure of the midline fascia. Upper abdominal midline incisions extend from the xiphoid process to the umbilicus. The fibrous linea alba is wider above the level of the umbilicus and therefore is more easily identified than the much thinner infra-umbilical linea alba. Extraperitoneal fat may then be swept aside in order to expose the peritoneum. This is best achieved at the lower aspect of the incision so that the position of the ligamentum teres hepatis and the falciform ligament may easily be identified when entering the abdominal cavity. The ligamentum teres hepatis may also be ligated and divided if it limits exposure within the operative field. Once the peritoneum is encountered, the surgeon should gently elevate it with haemostats and open it sharply in a longitudinal direction, taking great care to avoid injury to the underlying viscera. In the reoperative setting, the surgeon must be especially cautious in order to avoid injuring the intestine and/or other structures that may be adherent to the posterior surface of the linea alba; entering the peritoneal cavity just superior or inferior to the old incision may avoid adhesions and may potentially be an advantageous approach. Once the peritoneal cavity has been entered, the incision may then be extended as required to provide adequate surgical exposure. Excising the xiphoid process may be a necessary step, as this increases the operative field by four or more centimetres in width, and may provide better access to foregut structures and to the inferior vena cava and hepatic veins. When extending an upper midline incision inferiorly, the surgeon may circumnavigate the umbilicus to either the left or right side, or make a transumbilical incision. Care must be exercised if epigastric, umbilical or incisional hernias are unexpectedly encountered when creating a midline abdominal incision. Peritoneal entry should generally be carried out through the upper end of an infra-umbilical incision in order to avoid bladder injury. Placement of a urinary catheter preoperatively is very important because it decompresses the bladder and reduces risk of injury to it. Similarly, when approaching the pubic symphysis, the surgeon should incise the peritoneum more laterally, off the midline, in order to reduce the risk of bladder trauma (see Fig. 55.9 ).

Paramedian incision

Left or right paramedian incisions are placed lateral and parallel to the midline. The skin and subcutaneous fat are divided, and the anterior rectus sheath is incised vertically along the entire length of the incision. Rectus abdominis is then freed from the anterior sheath and retracted laterally. Great care must be taken to divide any tendinous intersections that are encountered and to ensure that segmental vessels are also ligated and divided. The tough membranous layer of the posterior rectus sheath and the peritoneum are then incised. This incision may be extended in a similar manner to the midline incision but its cranial extension is limited by the costal margin. The deep inferior epigastric artery passes between the posterior rectus sheath and the rectus muscle, either at or below the level of the arcuate line, and usually requires ligation when a low paramedian incision is carried out. These incisions may take longer to perform than other incision types and also have a higher risk of both vascular and nerve injury, but they have the advantage of being at lower risk for incisional hernia development than other vertical incision types (see Fig. 55.9 ).

Pararectus (Kammerer–Battle) and transrectus (mid-rectus) incisions

Pararectus and transrectus incisions are seldom used today because both result in denervation and vascular compromise with subsequent muscular atrophy. A pararectal incision is made along the lateral border of rectus abdominis, which is retracted medially. A transrectus incision splits the muscle along a vertical plane parallel to the site of a paramedian incision (see Fig. 55.9 ).

Component separation

Ventral incisional hernias are common and may be very challenging to repair. In 1990, Ramirez and colleagues described the component separation technique, which was originally developed to allow for primary closure of large midline abdominal wall defects. Even though the technique has evolved over time, its overall objective, to improve the integrity of the abdominal wall by permitting creation of a tension-free closure of the linea alba, has not changed. This objective may be achieved by utilizing one of several well-described techniques, including anterior component separation (open or endoscopic), retromuscular repair (Rives–Stoppa technique) and posterior component separation (with or without transversus abdominis release).

The open anterior component separation technique was originally described by Ramirez and colleagues and has been modified over time. Essentially, it involves the release of the aponeurosis of external oblique and elevation of rectus abdominis from the posterior rectus sheath. This creates a myofascial advancement flap that is capable of mobilizing each side of the anterior abdominal wall medially by up to 10 cm at the waist line, 5 cm in the epigastrium and 3 cm in the suprapubic region. In brief, following a midline laparotomy, a subcutaneous flap is raised that exposes the anterior rectus sheath. This dissection is then continued in the subcutaneous plane to approximately 2 cm or more lateral to the linea semilunaris. The aponeurosis of external oblique is then incised longitudinally, just lateral to the edge of rectus abdominis, and separated from the underlying internal oblique ( Fig. 55.10 ). A contralateral component release may also be carried out if a unilateral release does not permit closure of the defect. The defect should be closed and ideally reinforced with a sublay, underlay or onlay mesh.

Fig. 55.10, Open anterior component separation. The external oblique aponeurosis is incised longitudinally just lateral to the edge of rectus abdominis and separated from the underlying internal oblique muscle.

The Rives–Stoppa technique involves placement of a retromuscular sublay mesh, and is suitable for moderately sized defects because it will advance the rectus muscle to the midline by a maximum distance of 5 cm on each side. After a midline laparotomy is performed, the posterior rectus sheath is incised vertically 1 cm or less from the edge of the linea alba on one side ( Fig. 55.11 ). The dissection is continued in a superior and inferior direction for 5–8 cm. The retromuscular plane of the contralateral rectus abdominis is then entered in a similar way and lateral dissection next proceeds towards the edge of the rectus sheath envelope bilaterally. The preperitoneal space should be developed if the defect extends below the arcuate line. The posterior rectus sheath and transversalis fascia are then closed in a continuous fashion. A sublay mesh can then be secured in place, followed by closure of the linea alba. For larger defects a posterior component separation may be required. This is an extension of the Rives-Stoppa technique and involves division of the posterior aponeurotic sheath of the internal oblique muscle once the posterior rectus sheath has been incised at its most lateral edge. Dissection is carried out as far lateral, superior and inferior as necessary to close the defect. However, one major disadvantage of this technique is that dissection in the transversus abdominis plane (TAP) results in segmental nerve damage. To avoid this, Novitisky described a modification of the posterior component separation technique by performing a transversus abdominis muscle release (TAR). After the initial steps of the Rives-Stoppa technique are completed, the posterior rectus sheath in the upper third of the abdomen is incised again to expose the underlying fibers of transversus abdominis. Division of the posterior rectus sheath should be completed 0.5–1 cm medial to the linea semilunaris, ensuring that the perforating neurovascular bundles of the thoraco-abdominal nerves are identified and preserved lateral to this incision. The incision is continued in a superior and inferior direction and the arcuate line is divided. Transversus abdominis is then divided and separated from the underlying transversalis fascia and a plane is bluntly developed. A sublay mesh is secured in place, as has already been described.

Fig. 55.11, Posterior component separation (Rives–Stoppa technique). Following a midline laparotomy, the posterior rectus sheath is incised vertically 1 cm or less from the edge of one side of the linea alba and the rectus muscle divided off the sheath. The retromuscular plane of the contralateral rectus can then be entered in a similar way.

Transverse incisions

Upper and lower transverse incisions

Transverse abdominal incisions are frequently utilized in operations that are performed on neonates and children because their abdominal cavities have a more horizontal and ellipsoid orientation, whereas the adult abdomen has a shorter transverse than vertical girth (which favours a vertical midline incision for access). The nerve supply to rectus abdominis is segmental, and therefore transverse incisions that transect both the rectus sheath and muscle cause little damage to its innervation. The incision may also be extended laterally through the flat muscles along the line of the skin incision. Lateral abdominal muscles are richly innervated and usually heal without weakness (see Fig. 55.9 ).

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