The healing process of fracture is a complex and continuous process, which is usually divided into three stages from histological and cytological changes, as follows: 1. Hematoma mechanization phase, in which fibroblasts in the granulation tissue synthesize and secrete a large number of collagen fibers, which are transformed into fibrous connective tissue, connecting the two ends of the fracture and becoming fibrous links. 2. Primary bone scab formation phase, in which new bone is formed by the inner and outer periosteum immediately inside and outside the bone cortex. New bone, called internal and external bone scab, is continuously calcified and strengthened to achieve clinical healing of the fracture when it reaches a level sufficient to resist muscle contraction, shear and rotational forces, which generally takes 12-24 weeks in adults. 3. The period of scab remodeling and shaping, in which dead bone is removed and new bone is formed by the invasion of osteoblasts and osteoclasts, replacing the process of crawling. The original bone scab is replaced by lamellar bone to form a strong bony connection at the fracture site, which is completed in about 1-2 years.