Development of the human shoulder joint during the embryonic and early fetal stages: anatomical considerations for clinical practice.

Although several studies have been published regarding the morphology and anatomical variations of the human shoulder joint, most have dealt with adult individuals. Those looking into the development of the joint have been focused on specific structures or have observed specimens in advanced gestational stages. The goal of this paper is to perform a complete analysis of the embryonic and early fetal development of the elements in the shoulder joint, and to clarify some contradictory data in the literature. In our study, serial sections of 32 human embryos (Carnegie stages 16-23) and 26 fetuses (9-13 weeks) were analyzed. The chondrogenic anlagen of the humerus and the medial border of the scapula can be observed from as early as Carnegie stage 17, whereas that of the rest of the scapula appears at stage 18. The osteogenic process begins in week 10 for the humeral head and week 11 for the scapula. At stage 19 the interzone becomes apparent, which will form the glenohumeral joint. In the next stage the glenohumeral joint will begin delaminating and exhibiting a looser central band. Denser lateral bands will join the humeral head (caput humeri) and the margins of the articular surface of the scapula, thus forming the glenoid labrum, which can be fully appreciated by stage 22. In 24-mm embryos (stage 21) we can observe, for the first time, the long head of the biceps tendon (which is already inserted in the glenoid labrum by week 9), and the intertubercular sulcus, whose depth is apparent since week 12. Regarding ligamentous structures, the coracohumeral ligament is observed at the end of Carnegie stage 23, whereas the primitive glenohumeral ligament already appeared in week 10. The results of this study provide a detailed description of the morphogenesis, origin and chronological order of appearance of the main intrinsic structures of the human shoulder joint during late embryonic and early fetal development. We expect these results to help explain several functional aspects of the shoulder joint, and to clarify some contradictory data in the literature regarding this complex anatomical and biomechanical structure, helping future researchers in their efforts.