Sail sign (elbow)

Last revised by Leonardo Lustosa on 01 Aug 2022

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.

Video tutorial

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Cases and figures

  • Figure 1: sail boat (photo)
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  • Figure 2: elbow effusion (diagram)
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  • Case 1
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  • Case 2
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  •  Case 3
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  • Case 4: MRI equivalent
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  • Case 7
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  • Case 9
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