Sail sign – elevation of the anterior fat pad on a lateral radiograph of the elbow like a billowing sail indicating a joint effusion. Normally the anterior fat pad is concealed within the coronoid fossa or seen paralleling the anterior humeral line. When there is a joint effusion the anterior fat pad becomes elevated appearing as a subtle low density triangle. In the setting of trauma the sign usually heralds the presence of an intra-articular fracture; most often a radial head fracture in adults (as above) or a supracondylar humerus fracture in children. CT image is shown for anatomic correlation.
from our tumblr blog: http://radiologysigns.tumblr.com/post/26308421484