The Predictive Value of a Normal Radiographic Anterior Fat Pad Sign Following Elbow Trauma in Children

Abstract

The purposes of this study were to describe the characteristics of a normal anterior fat pad (AFP) and to determine the association between a normal AFP and the absence of fracture. A prospective cohort of children aged 1 to 18 years with elbow trauma underwent radiographic examination. All patients received standard orthopedic management and follow-up 7 to 14 days after injury. A pediatric radiologist evaluated all radiographs for the presence or absence of fracture and documented whether the AFP was normal or abnormal on the lateral view. The radiologist also recorded specific measurements of the AFP including the apical angle, which is formed by the intersection of the humerus and the superior aspect of the AFP. The interpretation of the AFP on the initial lateral radiograph was compared with the final patient outcome (fracture/no fracture). Two hundred thirty-one patients had elbow radiographs; 34 patients (15%) were lost to follow-up. A total of 56 fractures were identified: 49 (87%) on the initial radiograph and an additional 7 (13%) on follow-up radiographs. This latter group was defined as occult fractures. Among the 197 patients available for analysis, 113 (57%) had a normal AFP on the initial radiograph. Of these, 2 children had a final diagnosis of fracture. The sensitivity of a normal AFP was 96.4% (95% confidence interval, 86.6%-99.4%), and the negative predictive value was 98.2% (95% confidence interval, 93.1%-99.7%). There was a significant difference in mean AFP angle when the AFP was read as normal (14.7 [SD, 3.3] degrees) compared with when it was read as abnormal (27.0 [SD, 6.8] degrees) (P < 0.01). Our data suggest that a normal AFP is highly associated with absence of elbow fracture and that the determination of a normal AFP can be aided by measuring the apical angle of the AFP.