This cadaveric study evaluated ulnar variance during application of load following sequential sectioning of the interosseous membrane (IOM) and the triangular fibrocartilage complex (TFCC). Twelve cadaveric elbows underwent radial head resection and were randomized into two groups. Group 1 underwent transection of the TFCC followed by the IOM and Group 2 underwent the reverse. Twenty pounds of load were applied to the radius via an external fixator apparatus. Flouroscan images of the wrist were used to measure the change of ulnar variance. Radial head resection alone without any load resulted in no change in ulnar variance. With load, ulnar variance increased a median of 0.5 millimeters with a range of 0-2 millimeters. Radial migration was statistically increased with release of the IOM (median, 3.5 mm) or the TFCC and IOM combined (median, 9.5 mm). Overall, greater than 3mm of proximal radial migration with longitudinal traction after radial head resection indicated disruption of the IOM. Proximal radial migration greater than 6mm with load indicated disruption of all ligament structures.
Longitudinal instability of the forearm with radial head fracture (Essex-Lopresti lesion) is extremely rare and only seen in very high-energy injuries. Nonetheless, in the setting of a comminuted radial head fracture that cannot be repaired, the radius pull test may provide the clinician with a useful method to intraoperatively determine integrity of the IOM. Radial head resection alone is contraindicated in the setting of IOM insufficiency, as it is when the medial collateral ligament of the elbow is injured. As the authors indicate, the measurement of ulnar variance during pure longitudinal traction on the radius negates the possible apparent radioulnar instability that may occur in the setting of valgus instability of the elbow. Although this study correlates the ulnar variance findings with complete IOM disruption, little information is currently available with respect to partial IOM injuries and the possibility of secondary insufficiency of this structure. Nonetheless, this article provides clear guidelines that may be helpful to the clinician treating these traumatic injuries.
J Bone and Joint Surg