The effect of radial head fracture size on radiocapitellar joint stability.

OBJECTIVE The purpose of this study was to determine the effect of radial head fracture size on radiocapitellar stability. DESIGN Repeated measures using Instron materials testing machine. BACKGROUND Radial head fractures are common injuries and controversy exists as to the optimal management of displaced wedge fractures. METHODS Fractures were simulated in six fresh-frozen cadaveric radiocapitellar joints by removing sequential 20 degree wedges from the anterolateral aspect of each radial head until 140 degrees of the radial head was removed. Decreased shear load at the radial head during joint loading was used as an indicator of decreased stability at the radiocapitellar joint. Using a custom designed jig and employing a compressive joint load of 100 N, the maximum shear load at the radiocapitellar joint was measured at 30, 60, 90 and 120 degrees of elbow flexion. RESULTS There was no difference in the shear load between the intact specimen and that with a 20 degree wedge removed at all flexion angles (P>0.05). Shear load decreased with each increase in wedge size between 20 and 120 degrees (P<0.05). After 120 degrees, one-third the diameter of the radial head, the shear load was always less than 0.8 N. CONCLUSIONS This study demonstrated an inverse relationship between radiocapitellar joint stability and radial head fracture size. RELEVANCE Small radial head fracture fragments are biomechanically significant. Therefore, the use of an arbitrary fragment size as an indication for surgery should be reconsidered, particularly if there is an associated ligamentous injury.