Negative Ulnar Variance Lessens DRUJ Instability After DRUJ Disruption: A Biomechanical Analysis

Background: The purpose of this study was to perform a biomechanical investigation on the effect of ulnar variance (UV) on the stability of the distal radioulnar joint (DRUJ) prior to and after DRUJ sectioning. Methods: Ten cadaveric forearm specimens were included in the study and baseline UV was assessed radiographically. Radial motion relative to the ulna was evaluated using Intel real sense cameras and a custom developed program. The forearms were dissected, and a radial osteotomy was performed. Using a custom-made plate, radial stability was assessed with an UV of + 4, 0, and −4 mm by measuring the maximum and minimum radial position relative to the ulna during a simulated Shuck test. The volar radioulnar ligaments and triangular fibrocartilage complex (TFCC) were then sectioned, and testing was repeated at each UV state. Results: Sectioning significantly increased radial translation at neutral (P =.008), +4 mm UV (P =.008), and −4 mm UV (P =.018). There were no significant differences in translation between the 3 UV groups with the DRUJ intact (P =.124). The ulnar negative (−4 mm) state had significantly lower translation compared to the positive (+4 mm) (P <.001) and the neutral (0 mm) (P =.026) UV states. There were no significant differences between the positive and neutral UV groups with the DRUJ sectioned. Conclusions: Fixating the radius in −4 mm of ulnar negativity significantly decreased radial translation after sectioning the volar radioulnar ligament and TFCC. Ulnar variance had no effect on stability with an intact DRUJ.