<P> While immobilization and surgery may facilitate healing, a fracture ultimately heals through physiological processes . The healing process is mainly determined by the periosteum (the connective tissue membrane covering the bone). The periosteum is one source of precursor cells which develop into chondroblasts and osteoblasts that are essential to the healing of bone . The bone marrow (when present), endosteum, small blood vessels, and fibroblasts are other sources of precursor cells . </P> <P> There are three major phases of fracture healing, two of which can be further sub-divided to make a total of five phases: </P> <Ul> <Li> 1 . Reactive phase <Ul> <Li> i . Fracture and inflammatory phase </Li> <Li> ii . Granulation tissue formation </Li> </Ul> </Li> <Li> 2 . Reparative phase <Ul> <Li> iii . Cartilage callus formation </Li> <Li> iv . Lamellar bone deposition </Li> </Ul> </Li> <Li> 3 . Remodeling phase <Ul> <Li> v. Remodeling to original bone contour </Li> </Ul> </Li> </Ul> <Li> 1 . Reactive phase <Ul> <Li> i . Fracture and inflammatory phase </Li> <Li> ii . Granulation tissue formation </Li> </Ul> </Li>

What is the first stage in the healing of a bone fracture