OTA 2004 Posters
Reference Points for Radial Head Prosthesis Height: How to Avoid "Overstuffing" the Joint
Purpose: Metallic radial head implants are useful when the radial head cannot be reliably reconstructed and either the elbow or the forearm is unstable. Problems arise when the radial head prosthesis is too large, causing erosions of the capitellum and synovitis. We used three-dimensional computed tomography analysis to investigate the relative height (length) of the radial head relative to the lateral edge and central ridge of the coronoid process to be used as a reference point for optimal insertion of a radial head prosthesis.
Methods: Seventeen CT scans of the elbow with intact radius and ulna were analyzed. For each scan the plane defined by the proximal surface of the radial head was determined with use of three-dimensional CT. The anatomic coronal plane of the forearm was determined on the three-dimensional scan, and a two-dimensional image through the mid portion of the radial head was created in this plane. Finally, the distance between the plane of the articular surface of the radial head and parallel planes at 1) the most proximal aspect of the coronoid (the central ridge), and 2) the lateral edge of the coronoid articular surface were measured.
Results: The average distance between the planes defined by the radial head articular surface and the coronoid central ridge was 0.6 mm (range, &1.5 mm to 3.4 mm) The negative value means that the radial head is sometimes more prominent than the central coronoid ridge. The average distance between the planes defined by the radial head articular surface and the lateral edge of the coronoid articular surface was 2 mm (range, 0.7 mm to 4.1 mm) The radial head was slightly more prominent than the lateral edge of the coronoid process in every case, but to a variable degree.
Conclusion: Because the radial head was on average only 2 mm more proximal than the lateral edge of the coronoid process and because the key is not to overstuff the joint, a useful general guideline would be to place the plane of the articular surface of the radial head even with or just slightly more prominent than the lateral edge of the coronoid articular surface. Because of the substantial variability of the normal height of the articular surface of the radial head with respect to that of the coronoid, preoperative radiographs of the opposite elbow may be useful to avoid "overstuffing" the elbow.