Severe angulation and/or shortening of one of the forearm bones can be accompanied by fracture of the other bone or dislocation of a radioulnar joint. In a Monteggia fracture-dislocation, the ulnar fracture is associated with a dislocation of the radial head, at the proximal radioulnar joint and the radiocapitellar joint.
These are classified by AO/OTA, according to the morphology of the ulnar fracture, with qualifier (m). For example, the illustration shows a 2U2B3(m).
In most such cases, the radial head dislocates anteriorly or laterally; rarely is the dislocation posterior.
Forearm fractures are often the result of indirect mechanisms, such as a fall onto an outstretched hand, sporting activities, etc. Usually, the wedge fragment in an ulnar fracture is small. However, it may involve significant cortical bone loss due to the limited circumference and thick cortices, with minimal medullary cavity. The wedge fragment is frequently avascular.