The Fat Pad Sign

A lateral radiograph of the elbow shows a posterior fat pad sign (arrows) and elevation of the anterior fat pad (arrowheads) in a patient with a radial neck fracture (seen anteriorly on this image).

Facts

• Normal: elbow fat pads are intracapsular but extrasynovial, they are visible anteriorly to the elbow joint but not posteriorly.
• Effusion: elevation of both anterior and posterior fat pads are seen on lateral x-ray
• In an acute injury to the elbow, elevated posterior fat pad suggests the possibility of an intracapsular fracture
• Most common causes in children are supracondylar fracture, lateral epicondyle and separation of medial epicondylar ossification center
• Most common causes in adults are radial head or neck fractures, olecranon fractures, dislocations and fracture/dislocations
• Value of the posterior fat pad sign depends on its ability to predict an occult fracture in the absence of a radiographically visible fracture
• False-negative fat pad sign may occur if there is poor radiographic positioning, extracapsular abnormality or capsular rupture
• False-positive fat pad sign can be seen when the elbow is extended

References:

1. Goswami GK. The fat pad sign. Radiology 2002;222:419-420.

2. Skaggs DL, Mirzayan R. The posterior fat pad sign in association with occult fracture of the elbow in children. J Bone J Surg 1999;81:1429-1433.