Abstract
Positional information on the shoulder girdle (the clavicle and scapula) is important for a better understanding of the function of the upper limb in the locomotive system as well as its associated disease pathogenesis. However, such data are limited except for information on the axial position of the scapula. Here, we describe a three-dimensional reconstruction of the shoulder girdle including the clavicle and scapula, and its relationship to different landmarks in the body. Thirty-six human fetal specimens (crown-rump length range: 7.6-225 mm) from the Kyoto Collection were used for this study. The morphogenesis and three-dimensional position of the shoulder girdle were analyzed with phase-contrast X-ray computed tomography and magnetic resonance imaging. We first detected the scapula body along with the coracoid and humeral head at Carnegie stage 18; however, the connection between the body and coracoid was not confirmed at this stage. During development, all landmarks on the shoulder girdle remained at the same axial position except for the inferior angle, which implies that the scapula enlarged in the caudal direction and reached the adult axial position in the fetal period. The scapula body was rotated internally and in the upward direction at the initiation of morphogenesis, but in the fetal period the scapula body was different than that in the adult position. The shoulder girdle was located at the ventral side of the vertebrae at the time of initial morphogenesis, but changed its position to the lateral side of the vertebrae in the late embryonic and fetal periods. Such a unique position of the shoulder girdle may contribute to the stage-specific posture of the upper limb. Adequate internal and upward rotation of the scapula could help in reducing the shoulder width, thereby facilitating childbirth. The data presented in this study can be used as normal morphometric references for shoulder girdle evaluations in the embryonic and fetal periods.
Highlights
The shoulder girdle is the set of bones in the appendicular skeleton, which anchors the upper limb on each side to the axial skeleton [1, 2]
A total of 36 human embryo and fetal specimens (23 embryo specimens from Carnegie stage (CS) 16 to CS23 [crown-rump length (CRL) range: 7.6–28.0 mm] and 13 fetal specimens [Crown-Rump Length (CRL) range: 29.8–225 mm]) from the Kyoto Collection at the Congenital Anomaly Research Center of Kyoto University, Japan [21,22,23] were used for this study (Table 1)
CS16, CS18, CS19, and CS22 was illustrated by the author; each skeletal form including the scapula lacked close-up illustrations, and they were shown as a part of the whole upper limb system in each figure
Summary
The shoulder girdle (pectoral girdle) is the set of bones in the appendicular skeleton, which anchors the upper limb on each side to the axial skeleton [1, 2]. The acromioclavicular joint (ACJ) links the clavicle with the acromion on the scapula, while the shoulder or the glenohumeral joint provides articulation between the glenoid cavity of the scapula and the appendicular skeleton (the humerus) Movements in these joints can change the position of each component. More than 10 muscles are attached to the scapula, and collectively, they provide stability to the scapula as well as complex movements, such as elevation, depression, retraction (adduction), protraction (abduction), upward rotation, and downward rotation [1,2,3,4] Due to such movability, it is difficult to describe a default position of the shoulder girdle. The angle between the scapular plane and clavicle from the cranial view is around 60 degrees
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