The early development and ossification of the human clavicle--an embryologic study.

Morphologic studies of the early development of the clavicle were carried out in 46 human embryos and fetuses ranging in age from 6 to 12 weeks. We confirmed that the clavicle is formed by two membranous primary ossification centers appearing by 6 weeks and fusing approximately 1 week later. Cartilage at both ends of the clavicle then develops. In time, the medial cartilaginous mass contributes more to the growth in length of the clavicle than the lateral cartilaginous mass. The spatial orientation of both ossification centers and the development of enchondral bone formation at the ends of the clavicle lead to its characteristic shape. Interestingly, the primary ossification centers contribute little to the growth in length. The junction of the two centers of ossification is situated between the lateral and middle third of the clavicle and, consequently, does not correspond to the site of congenital pseudarthrosis, which is located in the middle part of the clavicle.