The pectoralis major muscle originates from the medial clavicle and lateral sternum and inserts on the humerus (Fig. 57.1). The major blood supply is thoracoacromial artery in addition to the intercostal perforators. The medial and lateral anterior thoracic nerves provide innervation for the muscle. The action of the pectoralis major is to flex, adduct, and rotate the arm medially. This muscle becomes important when additional soft tissue coverage is needed for an implant both in an aesthetic as well as a reconstructive setting.

Fig. 57.1 Anatomy of chest wall musculature.

Serratus anterior

The serratus anterior muscle runs along the anterolateral chest wall. Its origin is the outer surface of the upper borders of the first through eighth ribs and inserts on the deep surface of the scapula (see Fig. 57.1). Its vascular supply is derived equally from the lateral thoracic artery and branches from the thoracodorsal artery. The long thoracic nerve serves to innervate the serratus anterior, which acts to rotate the scapula, raising the point of the shoulder and drawing the scapula forward toward the body. To completely cover the implant with muscle in reconstructive surgery, often the serratus anterior must be elevated sharply to obtain the necessary coverage.

Latissimus dorsi

The latissimus dorsi muscle, which is a mirror image of the pectoralis major, arises from the lower thoracic vertebrae, the lumbar and sacral spinal processes, and the iliac crest. Its large, flat muscle belly converges into a flat tendon that inserts into the lesser tubercle of the humerus. The thoracodorsal artery provides the dominant vascular supply to the flap (Fig. 57.2). The subscapular artery originates from the axillary artery, gives off the circumflex scapular artery, and terminates in the thoracodorsal artery. This vessel, located in the posterior aspect of the axilla, gives off one or two serratus branches before entering the anterior undersurface of the latissimus dorsi muscle. The thoracodorsal artery is accompanied on its course by the thoracodorsal nerve and veins. The structures can be injured during an aggressive axillary dissection and therefore assessment of the pedicle in these patients is important in the preoperative planning.

Fig. 57.2 The blood supply to the latissimus dorsi muscle.

Rectus abdominus

The paired rectus abdominis muscles originate from the cartilage of the sixth, seventh, and eighth ribs and insert into the pubic tubercle and pubic crest (Fig. 57.3). The blood supply comes from the superior epigastric artery above and deep inferior epigastric artery below (Fig. 57.4). Within the muscle these main vascular sources may not have direct anastomoses with each other under normal physiologic conditions. Although the deep inferior epigastric system has been shown to be the primary vascular pedicle for this skin territory, the superior epigastric artery and vein are able to carry the lower abdominal soft tissue and comprise the vascular basis for the transverse rectus abdominis flap (Fig. 57.5). Additional blood supply is from the posterior perforating vessels accompanying the eighth through twelfth sensory and motor nerves. The musculocutaneous perforators that supply the flap are centered in the perumbilical area and emerge through the medial half of the rectus muscle to supply the subdermal plexus superficial to it (Fig. 57.6). Patient selection is important for this operation. Patients with an obese, pendulous abdominal panniculus, diabetics, and smokers carry a much higher risk of flap loss.