Break or split in a bone. A distinction can be made between simple and compound fractures. In simple fractures the skin remains intact; in compound fractures one or more pieces of bone protrude through the skin. In a comminuted fracture the bone is broken into several pieces or fragments. A division can also be made into complete or incomplete fractures. In a complete fracture the bone is broken into two or more pieces, whereas in incomplete fracture it is still intact in one place. An example of the latter is a ‘greenstick’ fracture, which can occur in children; because the young bone is so pliable and the periosteum so strong the bone does not break completely. A crack or fissure is also an incomplete fracture. Fractures are caused by force. They can however also occur as a result of normal pressure on the bone, if the bone is diseased (for example in osteo- porosis); this is known as a spontaneous fracture. Fractures are also classified by form: in a transverse fracture the line of break runs almost perpendicular to the length of the bone, in a slanting fracture the line slants through the bone and a fracture caused by twisting is a spiral fracture. Symptoms of a fracture are pain, swelling, abnormal position, abnormal movement and inability to move the affected limb oneself. Muscles go into spasm as a result of fracture, and if the fracture is complete the pieces of bone are forced to overlap. It is important to limit movement of the affected limb during transport by means of a splint. The precise position and nature of the fracture may be established by X-ray. In children it is often possible to join the bones accurately without surgery, after which a plaster cast is applied, but sometimes an operation to set the bone may be necessary, using plates or a pin through the marrow cavity to secure the broken bone. When a fracture has been set a blood clot forms between the two parts of the bone, in which blood vessels and connective tissue cells grow from the internal and external periosteum, forming soft connective tissue between the fractured parts, the so-called young callus. Connective tissue cells from the periosteum are able to form cartilage and bone. Calcium salts are deposited in the callus, so that after some time -sooner in children than in adults – a strong, hard connection between the fractured sections of the bone is built up. Disturbance of the normal process of bone healing can lead to the formation of a false joint. Other complications are nerve failure and disturbance of the blood supply as a result of damage to nerves and blood vessels by pieces of bone. Growing children may suffer damage to the growth plates, causing a difference in length in arms or legs.