In endochondral ossification, what is the first major event?

• A. Osteoid deposition by osteoblasts.
• B. Hyaline cartilage models develop.
• C. Periosteal bud invades.
• D. Secondary ossification centers form.

Answer: (B)

The first major event in endochondral ossification is the formation of a hyaline cartilage model that outlines the future bone. Mesenchymal cells condense and become chondrocytes, creating a cartilage scaffold in the shape of the eventual bone. Only after this template is in place do processes like invasion by blood vessels, formation of a bone collar, and ossification occur. So, the hyaline cartilage model developing first sets the stage for all later bone formation.