Rectus Abdommis Muscle Innervation

Sixteen cadaver dissections were performed to identify the location and course of the intercostal nerves in relation to the rectus abdominis muscle. Histochemical staining of fresh nerve biopsies was performed to assess the motor, sensory, and autonomic content of each nerve. Six to eight nerves passed inferomedially between the internal oblique and transversus abdominis muscles before entering the lateral confluence of the anterior and posterior rectus sheath or, in some cases, the posterior rectus sheath proper. The nerves, which contained varying numbers of sensory, motor, and autonomic fibers, passed under the muscle and became intramuscular at varying points along the width of the muscle, with most nerves entering the muscle in the lateral third in direct association with the lateral intercostal vascular pedicle. Two to three nerves entered the lower portion of the muscle below the umbilicus lateral to the inferior epigastric artery. During a partial muscle harvest of the medial two-thirds of the rectus abdominis muscle in these cadavers, it was possible to preserve innervation to the lateral third in several cadavers and to the portion of the rectus muscle lying below the arcuate line in all the cadavers. Innervation to a preserved medial muscle strip could not be preserved. Postoperative electromyographic evaluation of five patients undergoing TRAM flap breast reconstruction using the partial muscle harvest technique demonstrated that the retained lateral strip of muscle can remain innervated but with greatly diminished function, while the lower portion of the retained rectus muscle maintains near-normal function. We conclude that it is anatomically possible to preserve nerve fibers and function to the lateral third and particularly to the inferior portion of the rectus abdominis muscle when using the partial muscle harvest technique of TRAM flap elevation. Based on these results, a method for partial muscle harvest TRAM flap elevation is described. (Plant. Reconstr. Surg. 96: 105, 1995.)