What sign is evident on lateral projection and what is it caused by?
The anterior fat pad sign, also known as the sail sign or spinnaker sign. It is the result of a joint effusion elevating the normal anterior fat pad up and out of its normal location in the concavity of the humerus, which takes on a triangular shape on lateral projection.
In an adult what is the most likely diagnosis? What should be done?
An undisplaced intra-articular radial head fracture is most likely. The patient should be treated with that as the presumptive diagnosis and a repeat x-ray obtained in 7 to 10 days.
A sizable joint effusion indicates a probable fracture, most likely through the radial head. The fracture itself is not clearly visualised. Suggest re x-ray in 7 to 10 days.