Avoiding denervation of rectus abdominis in DIEP flap harvest II: an intraoperative assessment of the nerves to rectus.

BACKGROUND: The deep inferior epigastric artery perforator (DIEP) flap aims to reduce donor-site morbidity by minimizing rectus muscle damage; however, damage to motor nerves during perforator dissection may denervate rectus muscle. Although cadaveric research has demonstrated that individual nerves do not arise from single spinal cord segments and are not distributed segmentally, the functional distribution of individual nerves remains unknown. Using intraoperative nerve stimulation, the current study describes the motor distribution of individual nerves supplying the rectus abdominis, providing a guide to nerve dissection during DIEP flap harvest.
METHODS: Twenty rectus abdominis muscles in 17 patients undergoing reconstructive surgery involving rectus abdominis (DIEP, transverse rectus abdominis musculocutaneous, or vertical rectus abdominis musculocutaneous flaps) underwent intraoperative stimulation of nerves innervating the infraumbilical segment of the rectus. Nerve course and extent of rectus muscle contraction were recorded.
RESULTS: In each case, three to seven nerves entered the infraumbilical segment of the rectus abdominis. Small nerves (type 1) innervated small longitudinal strips of rectus muscle, rather than transverse strips as previously described. There was significant overlap between adjacent type 1 nerves. In 18 of 20 cases, a single large nerve (type 2) at the level of the arcuate line supplied the entire width and length of rectus muscle.
CONCLUSIONS: Nerves innervating the rectus abdominis are at risk during DIEP flap harvest. Small, type 1 nerves have overlapping innervation from adjacent nerves and may be sacrificed without functional detriment. However, large type 2 nerves at the level of the arcuate line innervate the entire width of rectus muscle without adjacent overlap and may contribute to donor-site morbidity if sacrificed.