Bone growth (ossification)

Author:  Dr. med. Gesche Riabowol (née Tallen), Last modification: 2023/01/25 https://kinderkrebsinfo.de/doi/e121106

Forming new bone is the major job of bone cells called osteoblasts. These cells first create an unmineralised basic tissue called osteoid. Later, the osteoid builds up calcium phosphate around the osteoblasts, thereby makes the bone hard and stable.

The process of bone forming depends on the type of bone.

• Short and flat bones (such as the skull and the clavicle) grow by laying down little sheets of bone layers (membranes) directly within their tissue (intramembranous ossification).
• Long bones expand in diameter, thus become thicker by membranous ossification around their central shaft (diaphysis).
• Longitudinal growth of the long bones starts at a cartilaginous disk, the so-called growth or epiphyseal plates (endochondral ossification). The epiphyseal plate of a long bone is situated between the diaphysis and its end (epiphysis).

The process of of bone formation begins with the proliferation of cartilage cells within the growth plate, followed by a step-by-step replacement of the cartilaginous tissue by bone tissue toward the diaphysis. Around the age of 20, bone growth usually stops due to the bony merge of diaphysis and epiphysis, thus closure of the epiphyseal plate.

Fractures or surgery as well as other mechanical injuries and radiotherapy in the area of the growth plate are associated with the risk of premature closure of the growth plate, which may affect bone growth. Based on this background, the localisation of a bone tumour in a child or adolescent is consid-ered an important factor in treatment planning in order to minimise the risk of stunted growth.