A fracture is a solution in the continuity of a bone, and is usually due to traumatism or to muscular contraction. The break may occur in any direction in the bone - transverse, oblique, or parallel to the long axis, or any modification. If the break is not complete of all fibers, it is known as a green-stick fracture; this is common in children. If there are several fragments it is called a comminuted fracture. If an opening to the surface is made, it is a compound fracture.

When a bone is broken, reparative processes take place and the bone is regenerated. After the fracture there is an extravasation of blood between the fragments. Proliferation of the cells of the periosteum occur, and calcareous matter is deposited, forming cartilage, or callus. This is slowly converted into bony tissue. At first there is an excess of it, but all except that immediately surrounding the fracture is absorbed. The callus is derived from the periosteum and from the medullary cavity. At the time of its formation new blood-vessels appear to assist in the nutrition. More or less deformity may accompany the process of repair, according to whether or not the broken fragments were carefully approximated.