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Bone healing or fracture healing is the repair of a fractured bone.
Requirements for healing
While immobilisation and surgery may facilitate healing, a fracture ultimately heals through physiological processes. In case of fracture, the chances of healing are determined to a large extent by the state of the periosteum (the connective tissue membrane covering the bone). This is the origin of the fibroblasts that participate in the healing of bone; bone marrow also participates in the healing process.
Phases of fracture healing
There are five phases of healing:
- Fracture and inflammatory phase
- Granulation tissue formation
- Callus formation
- Lamellar bone deposition
- Remodeling
After a fracture, the first thing that forms is a haematoma, similar to that seen elsewhere in the body. This is a clot of blood originating from the lacerated blood vessels in the bone and the periosteum.
Necrotic bone is then resorbed by osteoclasts, and the haematoma by macrophages. As the haematoma is resorbed, granulation tissue develops from the periosteum and endosteum. When this has completed, pluripotent cells migrate into the granulation tissue. These cells become chondrocytes and later osteocytes, that produce cartilage and bone respectively. The structure surrounding the fracture site is now slightly harder, this is a provisional callus. The area can be called a proper callus as time goes on, and more and more woven bone is made by the osteoblasts. This woven bone is initially remodelled into lamellar bone. With time, the bone is remodelled over the next few months, and the callus becomes smaller, as the trabeculae are formed along lines of stress.
Inadequate bone healing
Inadequate bone healing may predispose to further fractures at the same site, as well pseudarthrosis, undesired mobility in what appears to have become a new joint.
Medical Treatments
Bone morphogenetic proteins (BMP) are used to stimulate formation of new bone growth in areas such as spinal fusion.
Osseointegration
Osseointegration is the pattern of growth exhibited by bone tissue during assimilation of surgically-implanted devices, prostheses or bone grafts to be used as either replacement parts (e.g., hip) or as anchors (e.g., endosseous dental implants).
"Bone healing"