Soft Tissue Signs- The Elbow

Introduction

An equivocal fracture should be considered in the context of other information such as

• Patient history
• Clinical presentation
• soft tissue signs

This page will examine the soft tissue signs of bony injury of the elbow- what they are, their plain film appearances, their limitations, and their utility.

The Elbow

The Supinator Fatpad Sign

The supinator fat pad can be raised or obliterated as a result of bony injury, particularly to the radial neck. It is one of those unreliable soft tissue signs, but is useful as a guide to potential bony injury. The images below are of an injured elbow and a comparison view (comparison view was probably not necessary). The normal elbow (image 1) demonstrates a normal supinator fatpad as well as a normal anterior fat pad (just because the anterior fat pad is visible, does not suggest it is abnormal). Image 2 is a lateral view of the injured elbow which shows a distended joint which has pushed the anterior fat pad into view (sail sign), and caused the supinator fat pad to be minimally raised.

Image 1. Comparison View	Image 2. Injured Elbow

Tip
If you have trouble remembering whether it is the supinator fat pad sign or the pronator fat pad sign, think of a restaurant waiter. Waiters sometime carry soup bowls (i.e. "soupinator") in their elbows.
..... pronator fat pad at the wrist.... supinator fat pad at the elbow.

Supinator Fatpad Sign- Case 1

This 7 year old boy presented to the Emergency Department following major trauma. The lateral elbow image was taken as part of the trauma series in this case. I was asked by a colleague whether I thought the patient had an elbow fracture. The striking feature of this image was the raised supinator fat pad (white arrows). My suggestion was that this patient may have a radial neck fracture and that further imaging was required (further imaging was required regardless- a single view of the elbow was insufficient)

The radial head/neck fracture was well demonstrated on the AP/oblique view (arrowed)

The Elbow Fat Pad Sign

The fat pad sign or sail sign indicates that the patient has sustained an intra-articular injury. Importantly, it does not indicate that the patient has definitely sustained an intra-articular bony injury.

i.e. fat pad sign does not equal fracture

fat pad sign does indicate in increased chance of a fracture

There have been studies investigating the correlation between the fat pad sign and bony injury. These studies have reported an anterior fat pad sign indicates a probability of intra-articular fracture of approximately 70-80%, whereas a posterior fat pad sign indicates a 90% chance of intra-articular fracture. The anterior fat pad can be seen in a normal elbow. The posterior fat pad sign is never visible in a normal elbow.

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