Complete Rupture of the Pectoralis Major Tendon: Comparison of Magnetic Resonance Imaging and Intraoperative Images

The pectoralis major (PM) is an intricate anatomic structure. The muscle is divided anatomically into a clavicular and sternal head [1]. Notably, some authors describe a small, third abdominal head arising from the aponeurosis of the external oblique muscle [2] or from the fifth through seventh costal cartilages [3]. The clavicular head is composed of a single muscle segment, whereas the sternal head is composed of 6-7 separate muscle segments [1]. The sternal head constitutes approximately 80% of the PM muscle [1] (Figure 1). In addition to having complex muscle architecture, the tendon is bilaminar, with anterior and posterior layers/lamina [1,2]. The anterior layer/lamina is formed by contributions from the entire clavicular head and upper sternal muscle fibers and inserts onto the humerus slightly more distal than the posterior layer/ lamina [1,2]. The posterior layer is formed by contributions from the short, lowermost sternal fibers and inserts onto the humerus slightly more proximal than