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The Fat Pad Sign Following Elbow Trauma in Adults: Its Usefulness and Reliability in Suspecting Occult Fracture

Objective: An elbow joint effusion with no fracture seen on radiographs after acute trauma has become synonymous with occult fracture. This study evaluates the incidence of fracture in such cases as determined by MR imaging and the predictive value of an elbow joint effusion. Methods: Twenty consecutive patients whose posttrauma elbow radiographs showed an effusion but no fracture and who were suitable for MR imaging were recruited. The elbow effusion size, represented by anterior and posterior fat pad displacement, was measured from the initial lateral elbow radiograph. Suitable candidates underwent MR imaging using a bone marrow sensitive sequence. The time between injury and MR imaging ranged from 0 to 12 days (mean 4 days). Results: Seventy-five percent of the 20 patients who underwent MR imaging had radiographically occult fractures identified. Some (86.6%) of these fractures were located in the radial head, 6.7% were in the lateral epicondyle, and 6.7% were in the olecranon. Ninety percent had evidence of bone marrow edema. Fifteen percent had collateral ligament disruption identified on MR imaging, and 5% had a loose body. There was no change in patient management as a result of the additional imaging. The anterior fat pad displacement ranged from 5 to 15 mm (mean 9.25), and the posterior fat pad was elevated from 1 to 6 mm (mean 3.2). Conclusion: Our data using MR imaging suggests that fat pad elevation in the presence of recent trauma is frequently associated with a fracture. The size of the effusion, anterior/posterior fat pad elevation, or a combination of both does not correspond to the likelihood of an underlying fracture. MR imaging reveals a broad spectrum of bone and soft tissue injury beyond that recognizable on plain radiographs as demonstrated by all patients in this study.