Radial head fracture with posterior fat pad sign
Fall off a bike. Complaining of elbow pain
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The lateral film demonstrates anterior elevation of the anterior fat pad and a visible posterior fat pad. There is no fracture on the lateral view.
The oblique view shows a small fracture of the radial head.
Normally the posterior fat pad should not be seen at all and the anterior fat pad should be located adjacent to the anterior humeral cortex. The positive fat pad sign indicates a joint effusion and in the context of trauma should raise suspicion of haemorrhage due to fracture. In the adult patient one must consider a radial head fracture and in a child supracondylar fracture.
Remember that if there is acute trauma on a background of a prior history of joint pathology, e.g. rheumatoid arthritis, then a joint effusion may not be due to a fracture and be a red herring.