The radiological diagnosis of posttraumatic effusion of the elbow joint and its clinical significance: the 'displaced fat pad' sign.

Alterations occur in the radiological appearance of the soft tissues after injury to the elbow joint. These are due to displacement of the intra-articular fat pads by capsular distension when an effusion is present. A prospective study of 89 consecutive elbow injuries was undertaken in an attempt to assess the usefulness and reliability of these changes in the diagnosis of minor elbow injuries and the assessment of their clinical progress. In 61 elbows (69 per cent) there was no radiological evidence of an effusion and no evidence of bony injury. All quickly returned to normal. In 28 elbows (31 per cent) radiological evidence of an effusion was present. Twenty-three (80 per cent) of these were also found to have a fracture in, or adjacent to the elbow joint. In 9 elbows the fracture could not be seen on the initial radiographs. Because of the presence of an effusion, repeat radiographs were taken and a fracture discovered. The presence of an effusion was associated with an increase in the time required for full recovery.