endochondralis

Endochondralis, often referred to in English as endochondral ossification, is the process by which most bones form through replacement of a hyaline cartilage template with bone tissue. This mechanism is fundamental to the development of the long bones of the limbs, as well as many elements of the axial skeleton.

The process begins with a cartilage model produced by chondrocytes. A periosteal collar forms around the shaft, and a primary ossification center develops in the diaphysis. Blood vessels invade the cartilage, bringing osteoblasts and osteoclasts that begin replacing calcified cartilage with woven bone. As ossification progresses, the medullary cavity forms and the diaphysis lengthens.

Secondary ossification centers appear after birth in the epiphyses. The region between the epiphysis and the metaphysis remains as the growth plate (epiphyseal plate), a cartilage zone responsible for longitudinal growth. This plate contains proliferating chondrocytes that gradually mineralize and are replaced by bone as growth proceeds. After puberty, the growth plates close, leaving epiphyseal lines.

Endochondralis contrasts with intramembranous ossification, where bone forms directly from mesenchymal tissue without a cartilage stage. The endochondral route is essential for normal skeletal growth and for bone repair after fractures, although disruptions in its steps can lead to growth abnormalities or congenital skeletal disorders.