Bone has a strong ability to repair itself, and after a fracture, through a continuous healing process of inflammatory response, repair and shaping, the regenerated bone can fully restore the original structure and function of the fracture. However, there are many factors that can individually or in combination lead to delayed healing or non-healing of the fracture. (1) Delayed healing refers to a fracture that does not heal completely within the expected time frame. The fracture gap is primarily filled with granulation tissue or immature bone tissue. The fracture may still heal with appropriate subsequent treatment. Patients with delayed healing have localized pressure pain and indirect percussion pain with varying degrees of swelling and localized skin temperature may be elevated. Patients who do not heal may show abnormal local activity and may be associated with angulation or shortening deformity. The radiographic features of delayed healing are a low and late appearance of scab and a ‘fuzzy’ appearance of the fracture end. In some cases of delayed healing due to poor fixation, an increase in localized scabs is seen. (2) Non-healing The fracture does not heal within the expected time, the cellular activity and healing process at the fracture site have completely stopped and the fracture gap is dense fibrous tissue. The fracture will not join unless intervention is made. Dense fibrous tissue in the fracture gap. The typical radiographic presentation of a non-healing fracture is a widened, clearly visible fracture line without internal or external crust formation, sclerosis of the fracture end, closure of the medullary cavity, and eventually a pestle-like pseudoarthrosis. In addition, there may be localized osteoporosis. Infected bone non-union may show radiographic signs of osteomyelitis. The fixation may loosen and the deformity may recur in those who have had internal fixation. Fatigue tears may occur with internal fixation. In adults, the diagnosis of nonunion is not made until at least 6 months after the injury for long diaphyseal fractures. Nonunion of fractures can be classified as hypertrophic or atrophic. Hypertrophic is characterized by widening of the fracture end and excessive bone scab formation. Atrophic is characterized by no or minimal fracture response, sclerosis or resorption of the bone ends, and no external bone scab formation. Fracture nonunion may be followed by pseudarthrosis, which is manifested by closure of the medullary cavity, formation of a cartilaginous surface over the fracture end surrounded by a fibrous capsule and lined with synovial membrane, and a pseudarthrosis cavity containing fluid similar to that within a synovial joint. There is abnormal movement in the disjoint and the adjacent joint may be stiff.