Capitellum fracture

Case contributed by Dr Samir Benoudina

Presentation

Fall on an outstretched hand, from a stepladder.

Patient Data

Age: 35 years
Gender: Female
X-ray

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).

Annotated image

Mckee’s double arc sign

Case Discussion

Capitellum fractures are rare elbow injuries accounting for less than one per cent 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  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: 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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