Figure 1.

The formation of endochondral ossification and articular cartilage. Initially, mesenchymal cells undergo agglutination, mesenchymal cells in the center differentiate into chondrocytes and secrete type II collagen, chondrocytes continue to proliferate and secrete ECM, and cells around the agglutination express type I collagen and become cartilage membrane. The cartilage center’s cells then transform into hypertrophic chondrocytes, and blood vessels invade and create main ossification centers. Cartilage is progressively replaced by bone, and the cartilage membrane transforms into periosteum. At the ends of the elements, secondary ossification centers are created, and the epiphyseal cartilage plate is generated between the secondary and primary ossification centers. At last, the epiphyseal plate ossifies, leaving permanent articular cartilage at the element’s end.