Physiologic Superiority of the Anatomic Dominant Pedicle of the TRAM Flap in a Rat Model

Despite an extensive knowledge of the anatomic nuances of the rectus abdominis muscle and corresponding relationship to the vascularization of the skin of the abdomen, the clinical outcome when used as a musculocutaneous flap cannot always be predictable. Only a few human physiologic studies have been attempted to explain this discrepancy. Further laboratory investigations of the anatomy and physiology of the rat transverse rectus abdominis musculocutaneous (TRAM) flap suggest that this is a safer, comparable, yet inexpensive animal model for studying further the dynamics of this flap. By caliber and course, the major source vessel to the rectus abdominis muscle in the Sprague-Dawley rat enters superiorly as the cranial epigastric artery, which is a continuation of the internal thoracic (mammary) artery. Anatomic dissections in 13 rats revealed, on average, that 4.7 × 0.97 large musculocutaneous perforators emanated from each cranial epigastric artery at regular intervals which then proceeded directly to the overlying abdominal integument. Just below the umbilicus, a watershed is formed by small “choke” anastomoses to a frequently vestigial caudal epigastric artery or, more commonly, a true anastomosis with a branch of the deep circumflex iliac artery. In 10 additional rats, TRAM flaps encompassing the skin of the entire abdominal wall were then elevated so as to rely on a single pedicle, alternating randomly from either source. By laser Doppler flowmetry, blood flow by means of the larger-caliber superior pedicle exceeded twice that of the subservient inferior pedicle. Ultimate viable surface area of the superiorly based rat TRAM flap was 72.8 × 12.83 percent of the original as opposed to 44.8 × 18.07 percent of identical flaps if based inferiorly. Both differences were statistically significant (p < 0.002 and p < 0.03, respectively), verifying the physiologic superiority of the cranial epigastric artery as the dominant source vessel to the rat rectus abdominis muscle and that skin territory nourished by its perforators. (Plast. Reconstr. Surg. 96: 111, 1995.)