Orthopaedics A characteristic soft tissue finding in intra-articular injury of the elbow. Fat is normally present within the joint capsule of the elbow, but outside the synovium, 'hidden' in the concavity of the olecranon and coronoid fossae, and thus usually not visible on the lateral radiograph. Injuries that produce intra-articular hemorrhage cause distension of the synovium and force 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 sign indicates the presence of an intra-articular haemorrhage and effusion, which in turn is often associated with an intra-articular fracture (usually the radial head in an adult). In children, a sail sign suggests a supracondylar fracture of the humerus
Paediatrics See Spinnaker sail sign
sail sign Imaging A sharply demarcated triangular radiopacity seen in the mediastinum of 10% of normal children, which corresponds to the thymus and disappears on inspiration. See Rocker-bottom shadow.