On the lateral view of the right elbow, the anterior fat pad is elevated, creating a silhouette similar to a boat sail ( the anterior red line), called the "anterior fat pad sign," which indicates joint effusion. Besides, the posterior fat is visualized ( the posterior red line), which is not normally seen in this view, called the "posterior fat pad sign," again indicating elbow joint effusion and a fracture in the trauma setting.
Moreover, this is a perfect example of exhibiting how helpful is the external oblique view of the elbow to demonstrate better the radial head fracture (shown with red dots).