Endochondrale

Endochondrale, often encountered as endochondral ossification in English, refers to the process by which most bones of the axial and appendicular skeleton are formed through a cartilage precursor. It begins with the formation of a hyaline cartilage model that shapes the future bone. Mesenchymal cells differentiate into chondrocytes, creating a cartilage template that enlarges and matures. The primary steps involve chondrocyte proliferation and hypertrophy, calcification of the surrounding matrix, and invasion by vessels and osteogenic cells from the periosteum.

This invasion leads to the formation of a bone collar around the diaphysis and the establishment of a primary ossification center within the shaft. Osteoclasts and osteoblasts replace calcified cartilage with woven bone, which is later remodeled into lamellar bone, and a medullary cavity forms as cartilage is removed. Secondary ossification centers appear in the epiphyses, typically around birth, leaving a layer of articular cartilage and, in growing individuals, epiphyseal growth plates that enable longitudinal bone growth. After skeletal maturity, growth plates close to form epiphyseal lines.

Endochondral ossification is essential for the development of long bones such as the femur and humerus, and also contributes to the formation of vertebral bodies, pelvis, and base of the skull. It contrasts with intramembranous ossification, in which bone forms directly from mesenchyme without a cartilage intermediary. Regulation involves signaling pathways and hormones that coordinate chondrocyte proliferation, hypertrophy, and ossification timing. Disorders of this process can lead to growth abnormalities, chondrodysplasias, or osteoarthritis related to cartilage remodeling.