22u-D/4.1   Ulna, complete transverse, simple

Simple, complete transverse (≤30°) fractures of the ulna are unstable when the fragments are completely displaced.

An isolated ulnar fracture with substantial deformity is likely to be caused by a direct blow.

Note: In all cases of an isolated ulnar fracture, it is important to confirm the normal alignment of the radiocapitellar joint and specifically exclude a Monteggia lesion.