Radial head and neck fractures: anatomic guidelines for proper placement of internal fixation.

A cadaveric study of the radial head and neck was performed to determine the anterior and posterior limits for safe placement of internal fixation on the surface of the radial head or neck. A "safe zone" of approximately 110 degrees of radial head surface was first identified by cross-sectional anatomic dissections. This "safe zone" was then reproducibly confirmed relative to forearm position when viewed from a standard lateral approach. Because the proximal radioulnar joint cannot be directly visualized through the standard lateral approach, the zone was indirectly identified by making reference marks along the radial head and neck. To determine the position of the "safe zone" reference marks are first made along radial head and neck so as to bisect the bone's anteroposterior distance. Three such marks are made with the forearm in neutral rotation, full supination, and full pronation. Next, the posterior limit of the zone is determined by bisecting the reference marks made with the forearm in neutral rotation and full pronation. The anterior limit is determined by going nearly two thirds of the distance from the neutral mark to that mark made in full supination.