Disruption of the radiocapitellar line in the normal elbow

Disruption of the radiocapitellar line (RCL) can be a useful sign in injured elbows in children. Although originally described only in the true lateral projection, it has become generally accepted to apply the sign to any radiographic projection. However, it is not clear how to draw the line in the anteroposterior projection when there is prominent bowing of the radial shaft. Five cases are presented where the RCL, when drawn on radiographs of uninjured elbows, either did not pass through the capitellum (one case) or only passed tangential to it (four cases). In these cases, the elbow was not in the standard anteroposterior or lateral position. Radiologists and clinicians involved in trauma should be aware that radiographic positioning and normal bowing of the radial shaft can affect the validity of this sign and that it is best applied only to the true lateral projection as originally described.