Multifragmentary metaphyseal fractures of the ulna are classified as 2U1A3 fractures.
X-ray taken from Orozco R et al, (1998) Atlas of Internal Fixation. Used with kind permission.
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.