Anatomical study of innervated transverse rectus abdominis musculocutaneous and deep inferior epigastric perforator flaps

The present study investigated anterior cutaneous branches of the 10th, 11th and 12th intercostal nerves. Innervated transverse rectus abdominis musculocutaneous (TRAM) flap and deep inferior epigastric perforator (DIEP) flap are often used in breast reconstruction. To innervate these flaps effectively, the appropriate anterior cutaneous branches of intercostal nerves must be selected. Dissection of 40 sides of 20 cadavers (5 male, 15 female) was performed. Nerves were classified into four groups according to vertical location from rectus abdominis (RA) entry points. Group 1 was situated from 0–19% of the umbilicus-to-pubic tubercle distance; Group 2, 20–39%; Group 3, 40–59%; and Group 4, 60–79%. Mean number of nerves per side was 1.4 in Group 1, 1.2 in Group 2, 1.1 in Group 3 and 0.2 in Group 4. The arcuate line was situated 32 ± 9% below the umbilicus. Group 3 and 4 nerves tended to enter the RA more laterally than Group 1 nerves. Most nerves separated into 1–2 cutaneous branches while branching off several muscular branches. Several nerves in Groups 1 and 2 displayed no cutaneous branches. More muscular branches were present in Groups 1 and 2 than in Groups 3 and 4. Distance from lateral edge of the RA sheath to RA entry point was longer in Groups 1 and 2 than in Group 4. Cutaneous points, indicating entry points of a nerve into the dermis, were situated slightly more inferior than RA entry points. To innervate flaps effectively, a nerve entering the RA slightly superior to the expected sensory recovery area should be chosen. Clinically, Group 1 or 2 nerves seem to be selected in many TRAM or DIEP flap cases. If the cutaneous branch in Group 3 or 4 is easy to separate from RA, this can be included in the flap along with a main nerve, and might enable the flap to recover sensation in a wider area or reinforce the occasional lack of a sensory branch from Group 1 or 2. The present findings provide the basis for more precise dissection of TRAM and DIEP flaps, and should facilitate reliable preservation of sensation in flaps.