Endochondralen

Endochondral ossification is the biological process by which most bones are formed from a hyaline cartilage template. It is essential for the development of the majority of the skeleton, including long bones such as the femur, tibia, and humerus, as well as vertebrae and the base of the skull. The process begins in fetal life and continues after birth as bones grow in length, by the activity of growth plates.

The sequence begins with a hyaline cartilage model. Chondrocytes proliferate and hypertrophy, then the surrounding matrix calcifies and chondrocytes die. Periosteal blood vessels invade the calcified region bringing osteogenic cells that lay down woven bone, forming the primary ossification center in the diaphysis and creating the medullary cavity.

Secondary ossification centers appear in the epiphyses after birth. The growth plate remains as cartilage between diaphysis and epiphysis, allowing longitudinal growth until puberty when it ossifies and growth ceases. The articular cartilage remains as a persistent cartilage layer at joint surfaces.

Endochondral ossification contrasts with intramembranous ossification, where bone forms directly from mesenchyme. Clinically, disturbed endochondral ossification underlies skeletal dysplasias such as achondroplasia, and injuries to growth plates can affect bone length and alignment. In German-language texts, the process is referred to as endochondrale Ossifikation, with the adjective form endochondralen.