The elbow x-rays show a Monteggia fracture dislocation. There is a fracture of the proximal ulnar shaft with a dislocation of the radial head. The x-ray is interesting because the radial head dislocation can be appreciated only on the lateral view, not frontal.

The forearm bones are held together at the proximal and distal ends by strong ligaments. So, fractures of the radius and ulna commonly occur together. If only one bone is fractured, carefully look for a fracture/dislocation of the other bone. Thus, a fracture of the ulnar shaft is associated with a dislocated radial head at the elbow.

Dislocated radial head can be diagnosed by obliterated radio-capitellar line. Radio-capitellar line should be intact BOTH on frontal and lateral views. If not, suspect a radial head dislocation.

Reference: Grainger & Allison’s Diagnostic Radiology.