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.

Introduction:In general, the long head of the biceps brachii (LHB) tendon arises from the supraglenoid tubercle in the shoulder joint, and it has an important stabilizing mechanism for the humeral head in the shoulder joint. This case demonstrates that even if the LHB tendon can be palpated outside of the shoulder joint, it may disappear in the intertubercular sulcus (IS) and in the glenohumeral (GH) joint because of abnormal articulation.Patient concerns:This case involved the cadaver of an 82-year-old Japanese man (number 1936, cause of death: hepatocellular tumor), who was selected from the bodies used for gross anatomy practice at the Tokai University School of Medicine in 2017.Intervention:We removed the fat and skin around the shoulder joint for observational purposes and carefully examined the gross anatomy of the structures.Diagnosis:We suspected that the long head of the biceps brachii tendon arose from the lesser tubercle (LT) in the cadaver. In our case, it was found that the upper part of the subscapularis (SSC) tendon was torn first, and the succeeding degenerative changes and rupture of the LHB tendon were intra-articular.Outcomes:The long head of the biceps brachii tendon was found to be ruptured in the GH joint, and scar tissue developed between the distal stump of the tendon and the articular capsule, resulting in fusion with the LT.Conclusions:This case necessitates confirmation that the LHB tendon is present in the IS and in the GH joint to treat cases wherein failure of the dynamic stabilizing mechanism for the humeral head occurs.

In the literature, the passive movement of the biceps brachii during shoulder motion is unclear. This study investigated the passive movement of the long head (LHBB) and short head (SHBB) of the biceps brachii during shoulder rotation. We included 18 shoulders from 15 cadavers. At three shoulder positions (internal rotation [IR]20°, 0°, external rotation [ER]20°), the three sides of the triangle consisting of the confluence of the SHBB and LHBB, coracoid processes, and lesser tubercles were measured. The confluence angle of the LHBB and SHBB (Angle A) was calculated using the cosine theorem. The mean values for Angle A and standardized three sides of the triangle were statistically compared among the three shoulder positions. Angle A values were 13.5° ± 7.6° at IR20°, 15.2° ± 5.8° at 0°, and 15.7° ± 4.3° at ER20° with no significant difference (p = 0.096). The lengths of all three sides and Angle A were the smallest at IR20° and highest at ER20°. All the three sides revealed significant differences among the three shoulder positions (p < 0.0001). These results imply that morphological changes of the biceps brachii occur during shoulder rotation. These morphological changes in biceps brachii may contribute to shoulder joint stabilization by adjusting the forces the act on the tendons of both heads.