Development of the long head of the biceps brachial tendon: A possible explanation of the anatomical variations.

The anatomical variations of the proximal portion of the long head of the biceps brachii tendon (LHBT) are rarely observed in clinical practice. However, an increase in the rate of shoulder arthroscopic surgery has led to an increase in the observation of anatomical variations of this region. The aim of this work was to analyze the development of the LHBT in 23 human embryos ranging from the 6th to 8th weeks of development. The LHBT develops from the glenohumeral interzonal mesenchyme in the 6th week. By week 7, the myotendinous junction of the LHBT develops. The anlage of the LHBT is separated from that of the glenohumeral capsule during week 8. Our results suggest that the most important period for the LHBT development occurs between the 6th and 8th weeks of embryonic development. Alterations during this critical period may cause anatomical variations of the LHBT. An additional case report from our own experience is provided as Supplementary material.

Development of the Human Biceps Brachii Tendon and Coracoglenoid Ligament (7th-12th Week of Development).

The goal of this study is to clarify the development of the long head of the biceps brachii tendon (LHBT) and to verify the existence and development of the coracoglenoid ligament. Histological preparations of 22 human embryos (7-8 weeks of development) and 43 human fetuses (9-12 weeks of development) were studied bilaterally using a conventional optical microscope. The articular interzone gives rise to the LHBT, glenoid labrum, and articular capsule. During the fetal period, it was observed that in 50 cases (58%), the LHBT originated from both the glenoid labrum and the scapula, while in 36 cases (42%), it originated only from the glenoid labrum. The coracoglenoid ligament, first described by Sappey in 1867, is a constant structure that originates at the base of the coracoid process and projects toward the glenoid labrum zone, which is related to the origin of the LHBT. The coracoglenoid ligament was more easily identifiable in the 36 cases in which the LHBT originated only from the glenoid labrum. We suggest that the coracoglenoid ligament is a constant anatomical structure, is not derived from the articular interzone unlike the LHBT, and contributes to the fixation of the glenoid labrum in the scapula in cases in which the LHBT originated only from the glenoid labrum. We postulate that, when the LHBT is fixed only at the glenoid labrum, alterations in the coracoglenoid ligament could lead to a less sufficient attachment of the glenoid labrum to the scapula which could predispose to a superior labral lesion.