High index of suspicion is essential - some studies estimate 24% of these fracture patterns are missed in the ED. While the ulna fracture is usually apparent, the radial head dislocation can be more subtle. Failure to diagnose Monteggia's fracture can lead to chronic instability, recurrent dislocation, and limited range of motion of the elbow. Plain radiographs of the elbow and forearm are sufficient to make the diagnosis.
To avoid missing a Monteggia's fracture, draw a line longitudinally through the shaft of the radius. This line should bisect the capitellum (C) in any view, otherwise a dislocation or subluxation exists.