A fracture is any break in the bone or cartilage. It usually is a result of trauma but can be due to an acquired disease of bone such as osteoporosis or abnormal formation of bone in a congenital disease of bone such as osteogenesis imperfecta ("brittle bone disease").
Fractures are classified by their character and location. Examples of classification include "spiral fracture of the femur," "greenstick fracture of the radius," "impacted fracture of the humerus," "linear fracture of the ulna," "oblique fracture of the metatarsal," "compression fracture of the vertebrae," and "depressed fracture of the skull." A "comminuted fracture" is a fracture in which bone is broken into a number of pieces, as distinguished from a "compound fracture" in which the bone sticks through the skin.