Ossification style of the clavicle
- There are two modes of ossification: cartilaginous ossification and membranous ossification. Most bones undergo cartilaginous ossification. The representative of membranous ossification is the flat bone of the calvaria. The clavicle also has mostly membranous ossification (with some cartilaginous ossification). The clavicle is derived from a small bone connected to the calvaria of a jawless crustacean, such as an armor-clad lamprey eel, about 450 million years ago, which tells the history of the clavicle.
- The clavicle combines the ossification patterns of membranous bone at the center and cartilaginous bone at both ends. The timing of ossification is also characteristic. The clavicle is the earliest to begin ossification and the latest to complete fusion. Two ossification center appear in the connective tissue membrane at 5 weeks of gestation. Soon these two ossification points fuse. A secondary ossification point appears at the sternal end. This secondary ossification center begins to fuse at 18 to 25 years of age and is completed at 25 to 31 years of age. Occasionally, a small secondary ossification center may also appear at the acromion edge.