Anteroposterior (AP) radiograph of the left forearm (Fig. 56A) and AP and lateral radiographs of the left elbow (Figs. 56B and 56C) demonstrate an ulnar diaphyseal fracture at the junction of the proximal and middle thirds with apex anterolateral angulation, posterior displacement of the distal fracture fragment, and overriding of the fracture fragments, resulting in foreshortening. The radial head is dislocated anterolaterally. Inspection of the coronoid process on the lateral view of the elbow reveals minimal irregularity, but no other evidence for coronoid process fracture. Apparent soft tissue defect over the posterior proximal ulna is caused by distortion from the displaced and overriding fracture rather than from a penetrating soft tissue injury.

Anterior elbow dislocation, isolated radiocapitellar joint dislocation, isolated ulnar shaft fracture, ulna fracture with radiocapitellar joint dislocation.

The forearm functions as a ring composed of the radius and ulna as well as the proximal and distal radioulnar joints. A break in the ring is commonly associated with a fracture or dislocation in another part of the ring. When a
forearm fracture is seen on radiographs, both the wrist and the elbow must be evaluated to exclude associated dislocations and additional fractures. Monteggia fracture-dislocations are unstable injuries composed of a proximal ulna fracture and dislocation of the radial head. Failure to recognize the associated radial head dislocation may lead to long-term complications, requiring more extensive surgery.