Presentation
Fall on an outstretched hand, from a stepladder
Patient Data
The lateral film demonstrates:
- joint effusion
- semilunar fragment displaced anteriorly and superiorly consisting of capitellum and the lateral half of trochlea
- typical “McKee’s double-arc sign”: One arc representing the capitellum, and the second arc represents the ridge of the trochlea
Features consistent with a type IV capitellum fracture (according to Bryan and Morrey classification with McKee modification).
McKee’s double arc sign
Case Discussion
Capitellum fractures are rare elbow injuries accounting for less than one percent of fractures around the elbow. They are more common in females.
Mechanism of injury is usually a fall on the outstretched hand, the radius imparting a shearing force on the capitellum.
According to the Bryan and Morrey classification (with McKee modification), there are four types of capitellum fractures:
- type I (Hahn-Steinthal): large fragment containing substantial subchondral bone
- type II (Kocher-Lorenz): sleeve fracture with minimal bone
- type III: (Broberg-Morrey fracture): comminuted
- type IV: fracture includes a major portion of the trochlea
In this case, it is a type IV fracture. The characteristic finding on the lateral x-ray is the “McKee’s double-arc sign” because of the subchondral bone of the capitellum and lateral part of the trochlea.
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