The external oblique muscle free flap.

To date, the external oblique muscle has been considered to have a purely segmental vascular supply and therefore has been used surgically only as a pedicled flap. To better define the vascular anatomy and nerve supply of the muscle, we performed arterial injection studies and dissected the nerves that entered the muscle in 35 human cadavers. We found that in addition to the segmental arteries, one or two large branches of the deep circumflex iliac artery contributed significantly to the blood supply of the external oblique muscle in 33 of the 35 cadavers. We also found that the lateral cutaneous branches of the intercostal nerves entered and supplied the muscle near its origin from the rib in a strictly segmental pattern. These anatomic findings enabled us to transplant the external oblique muscle successfully as a free flap based on the deep circumflex iliac vessels in six patients. The muscle flap is thin, pliable, and can be combined with an iliac bone or an abdominal skin transplant. Its vascular pedicle is long (mean 12 cm) and of adequate diameter for microvascular repair. The donor scar of the flap is inconspicuously situated along the inguinal ligament and the iliac crest. Finally, since the muscle has a multiple nerve supply, it has the potential to provide several functional units at the recipient site when transplanted as a functional free flap.