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 ( = .008), +4 mm UV ( = .008), and -4 mm UV ( = .018). There were no significant differences in translation between the 3 UV groups with the DRUJ intact ( = .124). The ulnar negative (-4 mm) state had significantly lower translation compared to the positive (+4 mm) ( < .001) and the neutral (0 mm) ( = .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.

STUDY TYPE

Biomechanical Study.