The healing process of fracture is generally divided into three phases: inflammatory response phase, repair phase and shaping phase, and these three phases are not distinct. Fractures are usually divided into two categories: traumatic fractures and pathological fractures. The proliferation of osteoblasts in the outer and inner lining of the bone and the production of new bone mass are the basis for fracture healing. After the fracture, the bone heals completely through the process of hematoma formation, fibrous and bony scab formation and scab remodeling, restoring the bone to normal in structure and function. The fracture healing process can be divided into the following stages: 1. Hematoma formation In addition to the destruction of bone tissue, the fracture must also be accompanied by damage or tearing of nearby soft tissues. Bone tissue and bone marrow are rich in blood vessels, and the fracture is often accompanied by a large amount of bleeding, which fills the two broken ends of the fracture and its surrounding tissues, forming a hematoma. Because the blood vessels that nourish the bone marrow, bone cortex, and periosteum at the fracture site are subsequently broken, necrosis of bone marrow hematopoietic cells and precipitation of fat from the bone marrow can be seen within one to two days of the fracture and later surrounded by foreign giant cells to form a fatty “capsule”. Extensive ischemic necrosis can also occur in the bone cortex, and osteonecrosis is microscopically manifested by the disappearance of bone cells in the bone traps and their transformation into cavities. If the extent of osteonecrosis is not large, it can be absorbed by osteoclasts, and sometimes the dead bone can be shed, free and form dead bone fragments. 2. Fibrous bone scab formation About 2 to 3 days after the fracture, fibroblasts and new capillaries proliferating from the endosteal and eposteal membranes invade the hematoma, and the hematoma begins to mechanize. Most of these fibroblasts are essentially the predecessors of chondroblasts and osteoblasts. These proliferating tissues gradually bridge and fill the fractured ends, and then fibrosis occurs to form a fibrous scab, or temporary scab. After about 1 week, the above proliferating granulation tissue and fibrous tissue may further differentiate to form hyaline cartilage. The formation of hyaline cartilage is generally seen in the crustal area of the epiphyseal bone and less frequently in the intramedullary crustal area, which may be related to the lack of blood supply in the former. In addition, it is also related to the mobility of the fracture end and the excessive stress it is subjected to. However, the healing time of the fracture is delayed when there is excessive cartilage formation within the crust. The further development of the fracture healing process is the gradual replacement of the fibrous bone scab by new bone produced by osteoblasts. The bone formed at the beginning is bone-like tissue, and later calcium salt deposition occurs to form woven bone, i.e. bony scab. The cartilaginous tissue within the fibrous scab, like the chondrogenic bone during bone development, evolves into bone tissue by calcium salt deposition and participates in the formation of the bony scab. The woven bone formed at this time, because its structure is not dense enough, the arrangement of bone trabeculae is relatively disorderly, so it still does not meet the normal functional needs. 4.Bone scab reconstruction or remodeling After the above-mentioned bone scab is completed, the broken ends of the fracture are only connected by the infantile and irregularly arranged woven bone. In order to meet the physiological requirements of the body and to have a stronger structure and function, the woven bone is further remodeled into mature lamellar bone and the normal relationship between the cortical bone and the medullary cavity is restored. The reconstruction is carried out under the coordinated action of bone resorption by osteoclasts and new bone formation by osteoblasts, i.e., more new bone is formed at the site of maximum stress on the fractured bone, while bone that is not required for mechanical function is resorbed, so that the upper and lower ends of the fracture are reattached in their original relationship and the medullary cavity is reopened. In general, after the above steps, the fracture part is restored to the same structure as the original bone tissue and complete healing is achieved. Factors affecting fracture healing Systemic factors 1. Age: Children have strong bone tissue regeneration ability, so the fracture heals quickly; older people have weaker bone regeneration ability, so the fracture healing time is also longer. 2. Nutrition: Severe protein deficiency and vitamin C deficiency can affect the collagen synthesis of the bone matrix; vitamin D deficiency can affect the calcification of bone scabs and prevent fracture healing. 3, diseases: for example – diabetes, vascular insufficiency, osteoporosis, anemia, hormone deficiency, etc. Local factors 1. Local blood supply: If the blood supply to the fracture part is good, the fracture heals quickly, such as the upper end of the surgical neck of the humerus, fracture; conversely, if the local blood supply is poor, the fracture heals slowly, such as femoral neck fracture. The type of fracture is also related to the blood supply: for example, spiral or oblique fractures heal faster than transverse fractures because the fracture part has a large contact surface with the surrounding tissue and thus has a larger capillary distribution area to supply blood. 2. The state of the fracture end: poor alignment of the fracture end or soft tissue embedding between the fracture ends can delay healing or even prevent jointing. In addition, if the bone tissue damage is too heavy such as comminuted fracture, especially if there is too much periosteal damage, the bone regeneration is also more difficult. If the fracture is bleeding too much and the hematoma is huge, it will not only affect the contact of the fracture, but also affect the fracture healing by prolonging the hematoma mechanization time. 3, fracture end fixation: fracture end activity can not only cause bleeding and soft tissue injury, but also often only form fibrous bone scabs and difficult to form new bone. In order to promote fracture healing, good repositioning and fixation are necessary. However, long-term fixation can cause disuse atrophy of bone and muscle, which can also affect fracture healing. 4. Infection: Open fractures, where the skin and soft tissues are fractured, expose the fracture and often combine with septic infection, delaying fracture healing. If the fracture healing is impaired, sometimes too much new bone is formed and superfluous bone scab is formed, which has obvious bone deformation after healing and affects the recovery of function. Sometimes the fibrous bone crust does not turn into bone crust and fissures appear, and the two broken ends of the fracture can still move, forming a pseudo-joint, or even new cartilage is covered at the broken ends, forming a new joint.