Abstract
The anterior abdominal wall is a multilayered structure. The layers are:
1 Anterior Abdominal Wall
The anterior abdominal wall is a multilayered structure. The layers are:
skin
subcutaneous layer (superficial fatty or Camper’s fascia and deep membranous or Scarpa’s fascia)
musculoaponeurotic layer (rectus abdominis with rectus sheath)
muscle layer
fascia transversalis
extraperitoneal fat and parietal peritoneum
Function:
helps increase intra-abdominal pressure
accommodates abdominal expansion caused by ingestion, pregnancy, fat deposition or pathology
1.1 Skin and Subcutaneous Tissue
The direction of fibres is predominantly transverse with curving concave upwards in the dermal layer of skin, so vertical incision on skin generates more tension and a wider scar.
The subcutaneous tissue above the umbilicus is a single layer, but below the umbilicus, the deepest part of subcutaneous tissue is reinforced by elastic and collagen fibres, so there are two layers: superficial fatty layer and deep membranous layer.
The membranous layer is continuous inferiorly into the perineal region as superficial perineal fascia or Colles’ fascia.
The Camper’s fascia and Scarpa’s fascia are not well-defined layers. Scarpa’s fascia is best developed laterally, but not seen as a well-defined layer during vertical incision.
1.2 Musculoaponeurotic Layer
The musculoaponeurotic layer is a layer of muscle and fibrous tissue, and consists of two groups of muscles:
vertical: rectus abdominis and pyramidalis
oblique flank muscles: external oblique, internal oblique and transverse abdominis
□ Each rectus abdominis has three or more tendinous intersections. These intersections are above the umbilicus, but when found below it, then rectus sheath is attached to rectus muscle and the two structures become difficult to separate during a Pfannenstiel incision.
□ The direction of internal oblique is perpendicular to the direction of fibres of external oblique muscle, but in the lower abdomen, fibres of internal oblique arch more caudally and run in a direction similar to external oblique muscle.
□ The lower portion of transverse abdominis muscle is fused with the internal oblique, and during transverse incision of the lower abdomen, only two layers are discernible at the lateral margin of incision.
□ The direction of fibres of the flank muscles are transversely oriented. This is the reason that a vertical incision is more prone to tension and subsequently dehiscence compared to a transverse incision.
1.3 Rectus Sheath
The rectus sheath is a strong, incomplete fibrous compartment of rectus abdominis and pyramidalis muscles formed by the conjoined aponeurosis of the flat muscles of the abdomen.
For surgeons, the lower quarter of the rectus sheath is entirely anterior to the rectus muscles. Above this, it splits and encloses both ventral and dorsal aspect of the rectus sheath. This transition point is called the arcuate line (one-half of the distance between the umbilicus and pubic symphysis).
At the arcuate line, the midline ridge of the rectus sheath towards the umbilicus needs sharp dissection during a Pfannenstiel incision.
The linea alba transmits only small vessels and nerves to the skin, so a midline incision is relatively bloodless and avoids nerves.
2 Abdominal Incisions
Principles governing abdominal incision:
The incision must give ready access to the area of investigation and must allow extension if required.
The muscles must split in the direction of their fibres.
The incision must not divide nerves.
The rectus muscles may be cut transversely without weakening of the abdominal wall.
Drainage tubes should be inserted through separate, small incisions as their presence in a main wound hampers the strength of the ultimate scar.
2.1 General Laparotomy Incisions
incision on the anterior abdominal wall follows cleavage line/Langer’s line in skin
type of incision (see Figure 1.1):
◦ longitudinal: median/midline
— paramedian
◦ oblique and transverse
◦ high-risk incision
◦ minimally invasive/endoscopic surgery
2.1.1 Midline Incision
The incision runs along any length of linea alba from xiphoid to pubic symphysis, either above and below the umbilicus or both skirting the umbilicus.
This incision divides skin, linea alba, fascia transversalis, extraperitoneal fat and peritoneum.
The linea alba above the umbilicus is dense, strong, and 1 cm wide, so holds sutures well, but in the lower abdomen, the linea alba is very narrow, so poor suture technique predisposes to incisional hernia.
For laparoscopic surgery, insertion of the Veress needle is through the umbilicus followed by midline intra- or subumbilical port. Lateral laparoscopic ports (lateral to rectus sheath) should be made under transillumination and placed low to avoid damage of inferior epigastric vessels.
2.1.2 Paramedian Incision
Paramedian incision may extend from the costal margin to the pubic hairline.
It is a vertical incision; 2–2.5 cm away from, and parallel to, the midline.
The structures cut by a paramedian incision are the skin, anterior rectus sheath, rectus abdominis, posterior rectus sheath (above arcuate line), fascia transversalis, extraperitoneal fat and peritoneum.
2.1.3 The Lower Abdominal Transverse Incision
2.1.3.1 Pfannenstiel Incision/Suprapubic Incision
This incision is commonly used in most gynaecological laparotomies and obstetric surgery such as caesarean section for approaching pelvic organs.
Incision is horizontal, approximately 10–15 cm long, with slight convexity and made above the pubic symphysis, but just below the hairline (2 cm above the pubic symphysis).
The linea alba and anterior layer of rectus sheath are divided in the line of skin incision.
During this incision, injury to bladder, ilioinguinal and iliohypogastric nerves must be avoided.
2.1.3.2 Kustner Incision
The Kustner incision is also known as a modified Pfannenstiel incision.
Incision line is slightly curved, beginning below the level of the anterior superior iliac spine and extending just below the pubic hairline.
The incision is more time consuming and extensibility is limited, and there may be a chance of damage to inferior epigastric vessels.
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