Radial head dislocation with ulnar bowing

Case contributed by Leonardo Lustosa


Fall onto the outstretched hand while playing. Refuses to move the left elbow.

Patient Data

Age: 9 years
Gender: Male

Radiographs revealed a posterior radial head dislocation. There is a discrete bowing of the ulna noticed on the lateral projection, no fracture lines are seen. Also, elbow joint effusion is noted by the presence of the sail sign and the posterior fat pad sign.

A radial head dislocation with an associated ulnar shaft fracture is commonly referred to as a Monteggia fracture-dislocation.

(See annotated images below)

Ulnar bowing

Annotated image

Bowing of the ulna with a dorsal apex is noted in the proximal meta-diaphysis. 

Ulnar bow sign could not be assessed because the radiograph did not include the distal metaphysis of the ulna.

Radiocapitellar line

Annotated image

The radiocapitellar line was assessed and identified as not intersecting the capitellum, which indicates a radial head dislocation.

Case Discussion

Isolated radial head dislocations are rare injuries, the suspicion of a radial head dislocation should incite a thorough assessment of the elbow to avoid missing associated injuries, such as ulnar shaft fractures.

The radiocapitellar line is used to identify radial head dislocations or subluxations. It is drawn by extending a line along the axis of the radial neck towards the capitellum, and should normally intersect the center of the capitellum.

The ulnar bow sign is used to identify a bowing fracture of the ulna, which can be missed if not sought out properly. The greatest distance from the ulna cortex to a line drawn from the distal metaphysis to the olecranon should be <1 mm.

In the present case, the radial head dislocation is evident, but the more subtle ulnar bowing was initially missed. Thus, the injury is actually a Monteggia fracture-dislocation.

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