Coronoid process fracture
Fractures of the coronoid process of the ulna are uncommon and often occur in association with elbow dislocation.
Fracture of the coronoid process is thought to result from elbow hyperextension with either avulsion of the brachialis tendon insertion or shearing off by the trochlea .
Coronoid process fractures have been classified into three types within the Regan and Morrey classification system :
- type 1: avulsion of the tip of the coronoid process
- type 2: fragment involving <50% of the coronoid process
- type 3: fragment involving >50% of the coronoid process
The more clinically relevant and more widely adopted by orthopedic surgeon classification is introduced by O'Driscoll:
- type I: involves the coronoid tip and affects approximately one-third of the coronoid process
- type II: anteromedial facet involvement to a varying degree, with more medial involvement representing a more severe injury subtype
- type III: involving coronoid base with disruption of more than 50% of the coronoid body
The prognostic relevance of this classification is contentious, but there is some correlation with the pattern of associated injuries: smaller fractures are more likely to be associated with the “terrible triad” pattern of injury, whereas larger fragments tend to occur with anterior and posterior fracture-dislocations of the olecranon .
Coronoid process fractures may be diagnosed on a plain film series of the elbow, generally on a lateral or a 45° internal oblique view . CT is commonly necessary for fracture characterization of the fragment size, the degree of anteromedial involvement, and complex fracture-dislocation.