April 5, 2011

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).

  • 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
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.

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