Discussion | A. 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). |
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Reference | Jackman RJ, Pugh DG: The positive elbow fat pad sign in rheumatoid arthritis. Am J Roentgenol Radium Ther Nucl Med 1970 Apr;108(4):812-8. Murphy WA, Siegel MJ: Elbow fat pads with new signs and extended differential diagnosis. Radiology 1977 Sep;124(3):659-65. |
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