Fractures of the ulna with associ ated dislocation of the radial head are rare injuries in adults. they are also termed as Monteggia fractures after the surgeon who described the injury in early 19th century.
These injuries are more common in children and exact incidence in adults is unknown.
Clinical Presentation
The patient usually present with pain and swelling of the elbow and of upper third of forearm. Often the radial head can be palpatedone can palpate the dislocated radial head.
The affected limb should be carefully examined for any neurological deficit and vascular deficit.Radial nerve injuries are commonly associated with Monteggia fractures. 
Any associated injury should be noted
Radiography
True anteroposterior and lateral x-rays of the elbow must be included in any upper extremity injury that involves a displaced fracture of the ulna.
Alignment of the radial head can be found by a simple test.
A line drawn down the shaft of the radius through the radial head should bisect the capitellum regardless of the position of the forearm.
If it does not, the radial head is subluxated or dislocated.
[...] Monteggia fracture involves fracture of shaft of ulna and dislocation of radius. Following xray is of 39 years old male who suffered a motor vehicle injury to his upper limb and found to have a Monteggia fracture. Type I Monteggia Fracture Dislocation [...]