Fracture of the Radial Head with Effusion on Plain Films

 The anterior fat pad is normally visualized hugging the anterior cortex of the distal humerus. The posterior fat pad is not seen on normal views. Anterior displacement of the anterior fat pad and visualization of the posterior fat pad are compatible with a joint effusion. Radial head fractures may be extremely difficult to detect on plain film. In the setting of acute trauma, if an elbow joint effusion is present, the presumption should be that a radial head fracture is present, even if the fracture line is not visible