Rectus Abdominis

This vertically oriented muscle extends between the costal margin and the pubic region and it is enclosed by the anterior and posterior rectus sheaths. It is a type 3 muscle (two dominant pedicles) based on the superior epigastric artery and vein and inferior epigastric artery and vein. The pedicle length is 5-7 cm superiorly and 8-10 cm inferiorly.

Each of the dominant pedicles supplies just over one-half of the muscle. There is an anastomosis between these vessels that are usually sufficient to support the nondominant half if one of the two pedicles is ligated. Because of the larger size and easier dissection of the inferior epigastric vessel, this is usually used for free tissue transfer.

The motor innervation is supplied by segmental motor nerves from the seventh through twelfth intercostal nerves that enter the deep surface of the muscle at its mid to lateral aspects. The lateral cutaneous nerves from the seventh through twelfth intercostal nerves provide sensation to the skin territory of the rectus abdominis muscle. The size of the muscle is up to 25 x 6 cm. The skin territory that can be harvested is 21 x 14 cm2 and is based on musculocutaneous perforators11 (Fig. 8.9).

Flap Harvesting

The patient's position is supine. For a muscle flap the initial incision is located vertically over the muscle. For a musculocutaneous flap the incision extends around the skin island with an optional vertical incision extending to the muscle.

Incision of the anterior rectus sheath and dissection of the sheath from the muscle surface. Avoid muscle injury or disruption of the anterior rectus sheath at the tendinous intersection. The tendinous intersection is located at the level of the xiphoid, the umbilicus, and midway between the xiphoid and umbilicus. When a skin island is used, it is preferable to expose the muscle proximal to the skin island for accurate location of the muscle position. Then the skin island can be incised and its edges elevated to the lateral and medial borders of the rectus sheath. Separate the muscle from the posterior sheath at the distal aspect of the flap and beyond the skin island if a musculocutaneous flap is planned. Care is taken to avoid disruption of the posterior sheath below the linea semicircularis, below this line the posterior sheath consists only of transversalis fascia. After the muscle has been divided from the posterior sheath, the distal muscle is divided.

One of the complications of using this flap is the abdominal wall defect that may lead to weakness and possibly hernia formation. An advantage of this flap is the length of the pedicle and the ease of harvesting the flap with the patient in the supine position.42

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