A bone scab is a new bone like tissue that forms during the repair of a fracture. After a fracture occurs, stimulated by a variety of factors, a variety of cells at the fracture site proliferate and form new tissue to connect the broken ends of the bone, which is called a bone scab. Depending on the site of crust formation, there are two types of crusts: external crust and internal crust. The external bone scab is formed by the proliferation of extra-periosteal cells and is mostly shuttle-shaped, while the internal bone scab is formed by the proliferation of endosteal cells and is located within the bone marrow cavity. The formation of the scab undergoes a process and its composition is constantly changing, from a primitive scab in the early stages to a mature scab in the later stages. The process of scab formation is also the process of fracture healing, and the growth of the scab is influenced by the stresses at the fracture site. The growth and resorption of the bone scab are both important, with the early growth of the scab being used to join the fracture and the later shaping of the scab to repair the strength of the fracture site, and the scab is also an important indicator of fracture healing.