From the case:
Radiocapitellar line
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The radiocapitellar line (drawn in red) is intersecting the middle of the capitellum (painted in yellow) in both frontal and lateral projections.
Case Discussion
The radiocapitellar line is useful to assess the alignment on the elbow radiographs. The line is drawn by extending a line along the axis of the radial neck towards the capitellum. The line should normally intersect the center of the capitellum.
If the radiocapitellar line does not intersect the center of the capitellum, there may be a radial head dislocation.