Review Question - QID 3950

The clinical presentation is consistent with a coronoid tip fracture. This fracture pattern is associated with a radial head fracture and posterolateral ulnohumeral dislocation - together making up the terrible triad injury.

A terrible triad injury is the result of a valgus and supination injury and involves posterolateral elbow dislocation or lateral collateral ligament injury, radial head fracture, and fracture of the coronoid process. The elbow may dislocate postero-laterally with the anterior bundle of the MCL intact, but if the MCL is injured it is typically the last structure to fail. The coronoid fracture is typically a small fragment isolated to the tip. This is a result of a posteriorly directed force driving the coronoid into the trochlea prior to posterior elbow dislocation. CT scan is a useful modality when small or comminuted fragments are difficult to visualize on plain radiographs.

Steinmann reviews the anatomy, diagnosis, classification and treatment of coronoid fractures with a focus on surgical exposures and fixation techniques.

Doornberg et al. reviewed 67 coronoid fractures to determine whether type of coronoid fracture correlated with pattern of instability. They found strong associations between (1) large coronoid fractures and trans-olecranon fracture-dislocations, (2) small fractures and terrible-triad injuries, and (3) anteromedial facet fractures and varus posteromedial rotational injury mechanisms.

Doornberg et al. evaluated 18 patients with a fracture of the anteromedial facet of the coronoid. They found that malalignment of the anteromedial facet fragment was associated with arthrosis and a fair or poor result.

Figures A through D show consecutive 2.00 mm sagittal CT reformats demonstrating a small coronoid fracture fragment which was addressed with suture fixation.

Incorrect Answers:
Answer 1. Coronoid anteromedial facet fracture (not tip) in conjunction with LCL disruption can cause posteromedial rotatory instability. Coronoid tip fractures may be associated with posteroLATERAL rotatory instability
Answer 2. Capitellum fractures are not associated with coronoid fractures
Answer 4. Trans-olecranon fracture dislocations are associated with larger coronoid fracture fragments.
Answer 5. MCL injury is associated with valgus instability but not coronoid fracture