Sail sign (elbow)

The sail sign on an elbow radiograph, also known as the anterior fat pad sign, describes the elevation of the anterior fat pad to create a silhouette similar to a billowing spinnaker sail from a boat. It indicates the presence of an elbow joint effusion.

The anterior fat pad is usually concealed within the coronoid fossa or seen paralleling the anterior humeral line.  When there is a joint effusion, the anterior fat pad (which is intra-articular, but extrasynovial) becomes elevated.

Elevation of the anterior fat pad usually heralds the presence of an intra-articular fracture. In adults, this is usually a radial head fracture whereas in children, the commonest cause of a raised elbow fat pad is a supracondylar fracture. 

In the context of acute trauma, where a fat pad is raised and no fracture is demonstrated, an occult fracture should be suspected.

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See also

• sail signs
  • sail sign: the raised anterior fat pad on an elbow radiograph
  • thymic sail sign: normal thymus on a pediatric chest radiograph
  • spinnaker-sail sign (angel wing sign): thymus outlined in pneumomediastinum
  • retrocardiac sail sign: left lower lobe collapse on a chest radiograph
  • laryngeal sail sign: unilateral dilated laryngeal ventricle in vocal cord paralysis
• posterior fat pad sign (elbow)