The rat rectus abdominis myocutaneous flap: a true myocutaneous flap model

Investigations of experimental flaps in lower-order animals have concluded that the cutaneous vascular anatomy of "loose-skinned" animals is not analogous to that of humans. This is particularly relevant with respect to myocutaneous flaps. The interpretation of results of studies in lower-order animals raises questions as to the applicability of these data to the human condition.

To establish a true myocutaneous flap model in the rat, to define the microvascular anatomy and the cutaneous vascular territory of the rat rectus abdominis myocutaneous flap, and to determine its suitability for additional investigative study of myocutaneous flaps.

Forty-two Sprague-Dawley rats weighing 300 to 400 gm were divided into the following six experimental groups: Group 1 (microvascular anatomy, n = 5), microfil injection and microdissection; Group 2 (n = 5), India ink injection of an isolated superior or inferior epigastric artery pedicle; Group 3, flap control (n = 6); Group 4, superior epigastric (n = 17); Group 5, deep inferior epigastric (n = 16); and Group 6, bipedicle deep inferior epigastric (n = 3). Rectus abdominis myocutaneous flaps based on a single superior or inferior vascular pedicle, or on a double inferior vascular pedicle with an overlying cutaneous island extending from the costal margin to the pubis and anterior to the anterior axillary line, were raised and replaced. Control flap vascular pedicles were transected. Assessment of viability was performed at 7 days using two-dimensional planimetry, tetrazolium, and hematoxylin and eosin stain.

Injection studies revealed large (0.1 mm), direct, perforating vessels from the rectus abdominis muscle to the overlying cutaneous island. The cutaneous territory was defined by isolated pedicle india ink injection extended over the vertical muscle axis to the anterior axillary line and for a variable distance across the midline. All controls flaps were nonviable at 7 days. Superiorly based single-pedicle, and double-pedicle inferiorly based, flaps had 97% (SD, 0.03) survival of the cutaneous island. Single inferior pedicle flaps had 77% (SD, 0.07) survival of the cutaneous island with necrosis of the contralateral distal skin island. All flaps had 100% muscle survival.

The rat rectus abdominis muscle and overlying cutaneous island constitutes a true myocutaneous territory. This has not been described in a low-order laboratory animal. The flap can be based on single or double, superior or inferior, epigastric vessels with predictable flap survival. The superiorly based and double pedicle flap demonstrates nearly complete viability. This model should serve as a useful investigational tool in the laboratory study of myocutaneous flaps.