Ulna, extraarticular, multifragmentary

Multifragmentary metaphyseal fractures of the ulna are classified as 2U1A3 fractures.

The radial head can dislocate or subluxate posteriorly with respect to the capitellum (posterior Monteggia lesion). It’s uncommon to have a fracture in this part of the ulna without radial head dislocation and it’s uncommon to have a posterior dislocation of the radial head without fracture of the radial head.

The illustration shows a Jupiter Type B Posterior Monteggia without radial head fracture - an extremely uncommon event.