The left forearm and elbow x-rays show a dorsally angulated proximal ulnar fracture. The presence of an abnormal radiocapitellar line indicates a dislocation of the radial head. This combination is known as a Monteggia fracture dislocation.

The patient had a closed reduction of the fracture dislocation followed by operative management.

Always pay attention to the radiocapitellar line on the AP and lateral elbow x-rays. A line drawn through the centre of the radial head should always pass through the centre of the capitellum on both the AP and lateral views of the elbow.

The two bone system in the forearm has the properties of a ring bone; the fracture of one bone should be accompanied by a fracture of the other. If the 2nd bone is not fractured, always look for a dislocation affecting the non-fractured bone. An undiagnosed dislocated radial head can result in avascular necrosis.

Reference: Fundamentals of Diagnostic Radiology by Brant and Helms, 4th Edition.