PHYSIOLOGICAL 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 a bdominis muscle and corresponding relationship to the vascularization of the skin of the abdomen, the clinical outcome when used as a muscul ocutaneous flap cannot always be predictable. Only a few human physiol ogic studies have been attempted to explain this discrepancy. Further laboratory investigations of the anatomy and physiology of the rat tra nsverse rectus abdominis musculocutaneous (TRAM) flap suggest that thi s is a safer, comparable, yet inexpensive animal model for studying fu rther the dynamics of this flap. By caliber and course, the major sour ce vessel to the rectus abdominis muscle in the Sprague-Dawley rat ent ers superiorly as the cranial epigastric artery, which is a continuati on 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 i ntervals which then proceeded directly to the overlying abdominal inte gument. Just below the umbilicus, a watershed is formed by small ''cho ke'' anastomoses to a frequently vestigial caudal epigastric artery or , more commonly, a true anastomosis with a branch of the deep circumfl ex iliac artery. In 10 additional rats, TRAM flaps encompassing the sk in of the entire abdominal wall were then elevated so as to rely on a single pedicle, alternating randomly from either source. By laser Dopp ler flowmetry, blood flow by means of the larger-caliber superior pedi cle 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 statistica lly significant (p < 0.002 and p < 0.03, respectively), verifying the physiologic superiority of the cranial epigastric artery as the domina nt source vessel to the rat rectus abdominis muscle and that skin terr itory nourished by its perforators.