Irreducible anteromedial radial head dislocation due to transbrachialis buttonholing

Isolated radiocapitellar dislocations are rare; however our experience indicates that this is a dramatic injury whether acute or chronic. These patients present following hyperextension injuries. We propose the mechanism to be as follows: gentle hyperextension, varus torque, and rotation from pronation to supination. This sequence followed by elbow flexion will cause the radial head to dislocate anteromedially and sit on top of the brachialis muscle-tendon junction, which will cradle the radial head and serve as a block to reduction. In some cases the radial head will buttonhole through the brachialis muscle. As a result, it will appear as though these injuries can be reduced when the elbow is flexed however; the radial head will dislocate again upon elbow extension. In the case of an irreducible anteromedial radial head dislocation with no obvious intra-articular block to reduction, patients should be evaluated with MRI or ultrasound to assess for the possibility of transbrachialis buttonholing. Open surgical reduction is indicated. While evidence is still anecdotal at this point, patients respond well to surgical reduction and should be able to return to sport.