According to the UK National Health Service, the term “bone fracture” encompasses both cracks and breakages, and can happen to any bone in the body. The aim of this section is to describe and explain how the body sets about repairing a cracked or broken bone at the cellular level.
Immediately after a fracture occurs, a large blod clot (haematoma) develops at the fracture site. This clot deprives the surrounding bone cells (osteocytes) of blood and they consequently die. Intact cells surrounding the damage site then undergo rapid and repeated cycles of cell division (mitosis) with the progeny cells moving into the fractured area.
As summarised in this video (click link to open in new window), a collar of cartilage and bone (a callus) forms at the fracture site. Here, cells differentiate into chrondocytes (cartilage cells) and, closer to their edges, osteoblasts. Osteoblasts replace the central cartilage with bone, and this is remodelled by osteoclast action over the coming months (possibly over a year). In the next pages, the cellular level of bone development will be described. Bone cells surrounding the fracture undergo a "replay" of the embryonic processes that formed the bone in the first place. It is therefore appropriate to describe the process of bone formation during embryonic development, as will now be done, on the understanding that the processes involved are by and large applicable to bone restoration.
Continue to: Cartilage Models