Fracture healing is a complex and continuous process, which can be divided into three phases, hematoma inflammation mechanization phase, primitive bone scab formation phase, and bone scab remodeling and shaping phase. 1. Mechanization of hematoma inflammation: the broken end of the fracture and its surrounding hematoma are invaded by neutrophils, lymphocytes, mononuclear macrophages, and gradually remove the necrotic tissues, and then the hematoma is mechanized to form granulation tissue. 2. Primary bone scab formation period: it usually takes 3 to 6 months, first forming internal and external bone scabs, then gradually ossifying and forming new bone. 3. Scab remodeling and shaping period: this process takes about 1~2 years, the newborn bone trabeculae in the primitive bone scab gradually thicken, and the arrangement is gradually regular and dense.