Bone biology. II: Formation, form, modeling, remodeling, and regulation of cell function.

The formation, growth, maintenance, and healing of the skeleton require that bone be formed throughout life. Normal osteoblasts produce bone under a variety of conditions, including embryonic development, bone growth and remodeling, myositis ossificans or heterotopic ossification following soft-tissue trauma or fracture, and in response to neoplasms and infections. In addition, treatment with allogeneic and autologous bone-grafting, distraction osteogenesis, demineralized bone matrix fields, or exercise may stimulate the formation of bone. Despite the apparent differences among these treatments and conditions, the process of bone formation is the same. It can first be recognized when undifferentiated mesenchymal cells or preosteoblasts assume the appearance of osteoblasts and being to secrete a specialized extracellular matrix. This matrix mineralizes, and osteoblasts, surrounded by the mineralized matrix, become osteocytes. The appearance of osteoclasts begins the remodeling process that can convert immature woven bone into mature lamellar bone and resorb and replace mature lamellar bone.