Imaging (Important Lines)

If a line is drawn along the anterior part of the humerus (yellow line – Fig 1) on the lateral radiograph, then it should intersect the middle third of the capitellum. Failure to do this indicates that the capitellum has been displaced. There is often posterior displacement in association with supracondylar fractures.

Note that in Fig 2 the anterior humeral line passes through the anterior third of the capitellum, indicating posterior displacement in association with a supracondylar fracture.

A line drawn through the middle of the radius (Fig 3) should always bisect the capitellum since the radial head articulates with the capitellum (red line). This should occur in every direction, no matter which x-ray view is taken. If this is not the case, suspect dislocation of the radial head and remember that this can sometimes be associated with ulna fractures (Monteggia fracture-dislocation).

In Fig 4, the radiocapitellar line does not bisect the capitellum as there is a dislocation of the radial head.