Contribution of monoblock and bipolar radial head prostheses to valgus stability of the elbow.

BACKGROUND: The purpose of this study was to evaluate the stabilizing effect of radial head replacement in cadaver elbows with a deficient medial collateral ligament.
METHODS: Passive elbow flexion with the forearm in neutral rotation and in 80 degrees of pronation and supination was performed under valgus and varus loads (1) in intact elbows, (2) after a surgical approach (lateral epicondylar osteotomy of the distal part of the humerus), (3) after release of the anterior bundle of the medial collateral ligament, (4) after release of the anterior bundle of the medial collateral ligament and resection of the radial head, and (5) after subsequent replacement of the radial head with each of three different types of radial head prostheses (a Wright monoblock titanium implant, a KPS bipolar Vitallium [cobalt-chromium]-polyethylene implant, and a Judet bipolar Vitallium-polyethylene-Vitallium implant) in the same cadaver elbow. Total valgus elbow laxity was quantified with use of an electromagnetic tracking device.
RESULTS: The mean valgus laxity changed significantly (p < 0.001) as a factor of constraint alteration. The greatest laxity was observed after release of the medial collateral ligament together with resection of the radial head (11.1 degrees +/- 5.6 degrees). Less laxity was seen following release of the medial collateral ligament alone (6.8 degrees +/- 3.4 degrees), and the least laxity was seen in the intact state (3.4 degrees +/- 1.6 degrees). Forearm rotation had a significant effect (p = 0.003) on valgus laxity throughout the range of flexion. The laxity was always greater in pronation than it was in neutral rotation or in supination. The mean valgus laxity values for the elbows with a deficient medial collateral ligament and an implant were significantly greater than those for the medial collateral ligament-deficient elbows before radial head resection (p < 0.05). The implants all performed similarly except in neutral forearm rotation, in which the elbow laxity associated with the Judet implant was significantly greater than that associated with the other two implants. CONCLUSIONS AND CLINICAL RELEVANCE: This study showed that a bipolar radial head prosthesis can be as effective as a solid monoblock prosthesis in restoring valgus stability in a medial collateral ligament-deficient elbow. However, none of the prostheses functioned as well as the native radial head, suggesting that open reduction and internal fixation to restore radial head anatomy is preferable to replacement when possible.