The coronoid process is the anterior projection of the proximal ulna forming the anterior wall of the trochlear notch, articulating with the humerus and providing the anterior stability of the elbow joint. It is fractured in approximately 15 percent of elbow dislocations as the anterior joint surface is sheared off during posterior elbow dislocation. The coronoid is the keystone of elbow stability. Without adequate coronoid height the elbow cannot resist the valgus and posterolateral rotation forces of the reconstructed elbow after dislocation.
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| Ossification | The coronoid ossifies from the primary ulnar centre and has no separate ossification centre, distinguishing it from the olecranon which has a distinct apophyseal centre. |
The terrible triad of the elbow (posterior dislocation + radial head fracture + coronoid fracture) is the most complex elbow injury, requiring surgical fixation of all three components for stability. Coronoid fractures are classified by the Regan-Morrey system (by fragment height) and the O'Driscoll system (tip, anteromedial facet and basal fractures), which guide repair. Small tip fractures in simple dislocations can often be treated non-operatively, while larger fragments and anteromedial facet fractures require fixation. Anteromedial facet fractures cause varus posteromedial rotatory instability and early arthritis if missed. The anterior bundle of the MCL inserts on the sublime tubercle at the coronoid base.
Usually occurs with elbow dislocation; with a radial head fracture it forms the terrible triad, which is highly unstable.
A varus posteromedial rotatory injury fractures the anteromedial coronoid facet, causing elbow instability and early arthritis if untreated.
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