The pectoralis major muscle is a bilaminar muscle of the chest wall that performs five major functions: (1) flexion of the humerus as when lifting a box over one’s head, (2) adduction of the humerus as when bringing the arm close to the chest wall, (3) rotation of the humerus medially as when arm wrestling, (4) helping to abduct the humerus at the upper range of the arc of abduction as when reaching for an object on a high shelf, and (5) keeping the arm attached to the trunk of the body. Due to the amazing variation of stresses the muscle is subjected to as it performs these varied functions, the musculotendinous unit is susceptible to injury ranging from microtrauma to individual muscle fibers following overuse or misuse to full-thickness tearing with associated hematoma formation and cosmetic deformity. Most often, full-thickness tears occur at the tendon’s point of insertion into the crest of the greater tubercle of the humerus (Fig. 50.1).

Minor tears of the pectoralis muscle present clinically as anterior chest wall pain and require minimal treatment. Complete full-thickness tears that occur at the tendon’s point of insertion into the crest of the greater tubercle of the humerus present acutely with massive ecchymosis and hematoma formation and weakness of internal rotation of the humerus. A cosmetic deformity is often present with a bunching of the muscle in the anterior chest wall and a webbed appearance of the axilla (Figs. 50.2 and 50.3). Complete rupture of the musculotendinous unit requires prompt surgical repair, and failure to repair the rupture will result in further muscle retraction and calcification, worsening the functional disability and cosmetic deformity.

Magnetic resonance imaging and ultrasound imaging of the shoulder, proximal humerus, and anterior chest wall provide the clinician with the best information regarding any pathology including bursitis, tendonitis, and tumors of these anatomic regions. Both are useful in helping the clinician to identify abnormalities that may require urgent surgical repair such as complete pectoralis major muscle tears and/or tendon rupture. Both magnetic resonance imaging and ultrasound imaging will also help the clinician rule out occult pathology such as primary and metastatic tumors that may harm the patient.

The pectoralis major muscle is a broad, thick, fan-like bilaminar muscle, which makes up the majority of the chest wall muscles (Fig. 50.4). The pectoralis major lies beneath the breast in females. The muscle finds its origins from the anterior surface of the proximal clavicle, the anterior surface of the sternum, the cartilaginous attachments of the second through sixth and occasionally seventh ribs, and from the aponeurotic band of the obliquus externus abdominis muscle. These muscle fibers are laid out in an overlapping bilaminar pattern with some muscle fibers running upward and lateralward and others running horizontally. Other muscle fibers run downward and lateralward. All of this latticework of fibers coalesces into a broad flat tendon, which inserts into the crest of the greater tubercle of the humerus. It is at this distal insertion that the musculotendinous unit of the pectoralis major frequently ruptures (see Fig. 50.1). The motor innervation of the pectoralis major muscle is from the medial and lateral pectoralis nerve, which can be blocked to provide both surgical anesthesia for breast surgery as well as postoperative pain relief.

The benefits, risks, and alternative treatments are explained to the patient, and informed consent is obtained. The patient is then placed in the sitting position with the forearm resting comfortably on the ipsilateral thigh with the palm up (Fig. 50.5). The bicipital groove is then palpated (Fig. 50.6). The insertion of the musculotendinous unit of the pectoralis major muscle lies just medial to the bicipital tendon (Fig. 50.7). A high-frequency linear ultrasound transducer is placed in the transverse axis centered over the bicipital groove, and an ultrasound survey scan is taken (Fig. 50.8). The bicipital groove is identified with the biceps tendon, which appears as a hyperechoic ovoid structure lying within it (Fig. 50.9). The ultrasound transducer is then turned to a longitudinal axis and is moved inferiorly along the path of the biceps tendon following the margin of the medial aspect of the humeral head as it curves inward to the medial margin of the shaft of the humerus (Figs. 50.10 and 50.11). The insertions of the pectoralis major will be seen as

they attach to the humerus (Fig. 50.12). It is this point that the ultrasound-guided injection for pectoralis major muscle tear is carried out.