Endochondral Ossification: Correct Sequence of Cartilage-to-Bone Replacement

Endochondral ossification does not involve chondrocytes replacing osteoblasts. The correct sequence:

1. Mesenchymal condensation → chondrocytes form hyaline cartilage model.
2. Chondrocyte proliferation/hypertrophy → matrix calcifies.
3. Blood vessel invasion brings osteoprogenitor cells.
4. Osteoblasts differentiate and deposit bone matrix on calcified cartilage scaffold.
5. Primary ossification center forms in diaphysis; medullary cavity develops via osteoclast resorption.
6. Secondary ossification centers form in epiphyses postnatally.
7. Epiphyseal (growth) plate persists until skeletal maturity.

Key principle: Osteoblasts replace chondrocytes to form bone. Chondrocytes provide the template; they do not become bone cells.