Radiographic Appearance
Normal lateral radiograph of the elbow. B. Plain film
radiograph of the lateral elbow which reveals the classic elbow fat
pad sign. This is an invaluable soft tissue finding in cases of
intra-articular injury of the elbow. Fat is normally present within
the joint capsule of the elbow, but outside the synovium. Typically
"hidden" in the concavity of the olecranon and coronoid fossae, the
fat is usually not visible on the lateral radiograph. However,
injuries that produce intra-articular hemorrhage cause distension of
the synovium and forces the fat out of the fossa, producing
triangular radiolucent shadows anterior and posterior to the distal
end of the humerus. When present in a patient with a history of
acute trauma to the elbow, the fat pad sign indicates the presence
of an intra-articular hemorrhage, which in turn is often associated
with an intra-articular skeletal injury (usually the radial head in
an adult).From Wheelers Textbook of Medicine
Lateral View of Elbow:
- forearm flexed to 90;
- line from radial head to capitulum;
- film should demonstrate trochlea & capitellum
overlapping w/ space between the humerus and the radial head;
- soft tissue structures:
- anterior fat
pad:
Superficial part of anterior fat pad should be in front of coronoid fossa;
Iin normal elbow the anterior fat pad should be barely visualized;
Look for small radiolucent area between bony rim & moderate opaque shadows of brachialis;
With a joint effusion (2nd to a
minimally displaced radial head frx) there will be anterior &
superior displacement of anterior fat pad; - posterior fat pad
should not be seen at all;
A posterior fat pad sign and
no obvious frx, obtain an oblique radiograph to help rule out
supracondylar or lateral condyle frx;-
In the study by DL. Skaggs MD and R
Mirzayan MD (JBJS 1999) the authors prospectively examined a group
of children with acute elbow trauma and a posterior fat pad sign,
but no evidence of radiographic fracture;
- at three weeks, new radiographs were taken and were evaluated for
signs of fracture healing;
- they found that 34 out of 45 patients (76%) had evidence of a
fracture.
- 53% of patients had supracondylar frx, 26% had a proximal ulnar
frx, 12% had a frx of the lateral condyle, and 9% had a frx of the
radial neck;
- the authors conclude that children w/ a history of acute elbow
trauma and a posterior fat pad sign, should be treated as if they
have a non displaced frx about the elbow;
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