Anatomy - Abdominal wall closure - Techniques: loop suture and "small tissue bites"

1. Anterior Abdominal Muscles

Rectus abdominis muscle: Straight abdominal muscle within the rectus sheath with 3-4 tendinous intersections (intersectiones tendineae) that are fused with the anterior layer of the rectus sheath.

Pyramidalis muscle: Originates from the superior pubic ramus and inserts into the linea alba, located ventrally to the rectus abdominis muscle in its own sheath within the anterior layer of the rectus sheath.

2. Layered Structure of the Anterior Abdominal Wall

Rectus sheath: Encloses the rectus abdominis muscle; above the midpoint between the navel and symphysis, it is differentiated into an anterior and a posterior layer; the posterior layer ends here in the form of the arcuate line; above this line, the external oblique muscle inserts into the anterior layer of the rectus sheath, the internal oblique muscle into both the anterior and posterior layers, and the transversus abdominis muscle into the posterior layer.

Linea semilunaris: Transition zone between the aponeuroses of the lateral abdominal muscles and the lateral edge of the rectus sheath.

Linea alba: Approximately 1 cm wide, firm connective tissue strip between the right and left rectus sheath, extending from the sternum to the symphysis.

Transversalis fascia: Above the arcuate line, it covers the posterior layer of the rectus sheath internally, below the line it lies directly on the rectus abdominis muscle.

3. Internal Relief of the Abdominal Wall

Median umbilical fold: Median peritoneal fold running from the navel to the bladder, containing the median umbilical ligament (fibrous cord = urachus remnant).

Medial umbilical fold: Paired peritoneal fold, containing on each side the medial umbilical ligament = obliterated remnant of the bilateral umbilical artery, umbilical artery.

Lateral umbilical fold: Paired peritoneal fold, beneath which lies on both sides the inferior epigastric artery with two accompanying veins each.

4. Conduits

a) Arteries

Superior epigastric artery: Continuation of the internal thoracic artery, anastomoses at the level of the navel with the inferior epigastric artery.

Inferior epigastric artery: Arises from the external iliac artery and runs like the aforementioned artery on the dorsal surface of the rectus abdominis muscle within the rectus sheath.

Superficial epigastric artery: Originates from the femoral artery and distributes after crossing the inguinal ligament in the subcutaneous tissue of the anterior abdominal wall.
Posterior intercostal arteries VI – XI and subcostal artery: Originate from the thoracic aorta; their terminal branches run obliquely downward between the internal oblique muscle and the transversus abdominis muscle and extend from the lateral side into the rectus sheath, where they anastomose with the superior and inferior epigastric arteries.

b) Veins

Superior epigastric veins: Accompany the artery of the same name; anastomose with branches of the inferior epigastric vein and drain into the internal thoracic veins.

Inferior epigastric vein: Branches into accompanying veins of the inferior epigastric artery and drains into the external iliac vein.

Superficial epigastric vein: Runs parallel to the artery of the same name (see above).

c) Lymphatic Vessels

Superficial lymphatic vessels: Above the navel, they lead to the axillary lymph nodes, below to the inguinal lymph nodes.

Deep lymphatic vessels: Generally run parallel with the blood vessels; reach the parasternal, lumbar, and external iliac lymph nodes.

d) Nerves

Intercostal nerves VI – XII: As ventral branches of the thoracic nerves VI – XII; they enter the abdominal wall behind the costal cartilages between the internal oblique muscle and the transversus abdominis muscle; motor branches supply the anterior and lateral abdominal muscles, the sensory branches the abdominal skin.

Iliohypogastric nerve, ilioinguinal nerve, and genitofemoral nerve: Participate in the motor and sensory innervation of the lower abdominal region and genitalia.

Function and Tension Systems of the Abdominal Wall

Due to their distance from the spine, the straight abdominal muscles can exert significant leverage on the spine. The four oblique muscles are activated synchronously when bending forward, acting synergistically and thus supporting the rectus muscles.

The contraction of the abdominal muscles, diaphragm, and pelvic diaphragm creates the abdominal press. Since the diaphragm is significantly weaker compared to the abdominal muscles, an effective abdominal press is only achieved by closing the glottis and retaining air in the lungs, which, being air-filled, serve as a counterforce to the diaphragm.

In an upright position, the abdominal wall muscles bear the weight of the abdominal cavity contents. The weight of the viscera increases from cranial to caudal, and so does the load on the abdominal wall, which explains why the abdominal wall bulges more below the navel. Regarding a median laparotomy, there is twice the wall tension here as laterally, with a simultaneous increase from cranial to caudal. Due to the interweaving of the abdominal muscle aponeuroses along the midline, functional muscle loops are formed.

The integrity of the abdominal wall thus plays a crucial role in terms of physical resilience.

Mechanics

The mechanical demands that a fascial closure must meet primarily depend on the intra-abdominal pressure. While it is approximately 0.2 kPa at rest, the maximum pressures are just under 20 kPa (= 150 mm Hg). However, the required suture holding force for a secure fascial closure also depends on the diameter. For example, the required suture holding force for an abdominal circumference of 100 cm and an intra-abdominal pressure of 20 kPa is on average 16 N/cm.