Variation of insertion of the pectoralis major in a cadaveric study

Rationale: Typically, the tendon of the pectoralis major inserts into the crest of the greater tubercle of the humerus. However, anomalous insertion sites of the pectoralis major tendons have been noted. Patient concerns: The cadaver of a 95-year-old Japanese man was selected from the bodies used for gross anatomy practice at the Tokai University School of Medicine in 2018. Diagnosis: In this cadaver, the left side of the pectoralis major tendon appeared to insert at the crest of the greater tubercle and lesser tubercle of the humerus, forming a tunnel measuring 2.5 cm in total length. Intervention: We removed the fat and skin around the shoulder joint and upper extremity for observational purposes and carefully examined the structures during gross anatomy. Outcomes: The medial side of the insertion of the pectoralis major tendon was not into the humerus but had combined with the tendon of the latissimus dorsi, which then loosely inserted into the humerus. As the roof and both walls comprised the tendon of the pectoralis major and the floor was formed by the tendon of the latissimus dorsi and humerus, the structure formed a tunnel. Lessons: This study is important for orthopedic and rehabilitation physicians in treating diseases of the long head of the biceps brachii tendon. As part of management, the condition of the tendon of the pectoralis major should be confirmed using magnetic resonance imaging or echocardiography.