Ulna, articular, coronoid

Isolated fractures of the coronoid are classified according to the AO/OTA as 2U1B2 fractures.

This fracture has the following qualifiers:
• n – involving the sublime facet
• o – tip (avulsion)
• p – < 50% (illustrated)
• q – ≥ 50%

An isolated fracture of the anteromedial facet of the coronoid process is associated either with avulsion of the origin of the lateral collateral ligament (LCL) complex from the lateral epicondyle or fracture of the olecranon or both.

Transverse fractures (Mayo type I) of the coronoid tip include the capsular attachment and average more than 1/3 of the total coronoid height. They may have smaller or larger bone fragments.

Anteromedial facet fractures (Mayo type II) may be small or large.

Larger fractures may represent an avulsion of the anteromedial facet with the anterior band of the medial collateral ligament attached. This creates varus posteromedial instability.

Basilar fractures (Mayo type III), typically one or two large fragments.

Irreparable coronoid fractures, because of extreme comminution and/or osteoporosis, are occasionally encountered.

Isolated coronoid fractures are extremely rare and when seen, suspect a spontaneously reduced dislocation and look for elbow instability. The coronoid is almost always fractured in association with a dislocation of the ulnohumeral joint or a more complex proximal ulna or olecranon fracture.

Coronoid fractures occur in several patterns (described above). They must be assessed with care.

Fragments which appear small on a lateral x-ray may be larger than suspected. A CT is warranted to better determine the fragment’s exact size. Particularly deceiving are small anteromedial facet impaction fractures, which may be associated with posteromedial varus instability of the elbow. In general, the larger the coronoid fragment, the greater its potential effect on elbow stability.

The above x-rays, before and after reduction of a dislocated elbow, show a large coronoid fragment, still displaced after the elbow joint is reduced.

Coronoid fractures are often associated with ligament disruption, eg, LCL tears.

Occasionally – with small anteromedial facet fractures and complete elbow dislocation – the medial collateral ligament is avulsed from the medial epicondyle.

This X-ray shows an anteromedial facet fracture with a LCL injury.