posterior fat pad

Radial Head Fracture

The two abnormal findings above are a posterior fat pad (circle) and a radial head fracture (arrow).  This patient may be given a sling for comfort and follow up with an orthopedic surgeon.  

Radial head fractures are typically from a FOOSH injury as the radial head is driven against the capitellum.  Patients will complain of pain with passive ROM of the Forearm.  Radial head fractures are classified as four different types (treatment in parentheses) by the Mason classification (1):

Type I: nondisplaced (brief sling for comfort, early ROM)

Type II: Marginal impaction, displacement and angulation ( same as type I unless no improvement)

Type III: comminuted radial head (radial head excision)

Type IV: any of the above plus elbow dislocation (treat fracture and dislocation)

In evaluating the elbow radiograph, remember that a small anterior fat pad may be normal, but a posterior fat pad or effusion is always abnormal (posterior = pathologic).  A large anterior fat pad, or sail sign (in that it looks like a sail) is also pathologic.  Much like a supracondylar fracture in kids, radial head fractures can be occult on XR.  Pain over the radial head, pain with passive ROM, and an abnormal fat pad should clue you in to the diagnosis.  

Helpful test taking hint: Radial head fractures are the most common occult elbow fractures in adults, while supracondylar fractures are the most common occult elbow fractures in kids.  

1. Wheeless’ Textbook of Orthopedics.