Distal Metaphyseal Ulnar Shortening Osteotomy Fixation: A Biomechanical Analysis

Purpose Ulnar shortening osteotomy can be used to treat ulnar impaction syndrome and other causes of ulnar wrist pain. Distal metaphyseal ulnar shortening osteotomy (DMUSO) is one technique that has been proposed to reduce the complications seen with a diaphyseal USO or a wafer resection. However, to our knowledge, the optimal fi xation construct for DMUSO has not been studied. We sought to characterize the biomechanical stiffness and rotational stability of different DMUSO constructs. Methods A DMUSO was performed on 40 human cadaveric ulnas using 4 different fi xation constructs (10 specimens per group): one 3.0 mm antegrade screw; two 2.2 mm antegrade screws; one 3.0 mm retrograde screw; and two 2.2 mm retrograde screws. Biaxial testing using axial load and cyclical axial torque was performed until failure, defined fi ned as 10 degrees degrees of rotation or 2 mm displacement. Specimens were assessed for stiffness at failure. Bone density was assessed using the second metacarpal cortical percentage. Results Bone density was similar between all 4 testing groups. Of the 4 groups, the 2 ante- grade screw group exhibited the highest rotational stiffness of 232 +/- 102 Nm/deg. In paired analysis, this was significantly fi cantly greater than 1 retrograde screw constructs. In multivariable analysis, 2-screw constructs were significantly fi cantly stiffer than 1 screw and antegrade constructs were significantly fi cantly stiffer than retrograde. Maximum failure torque did not differ with orientation, but 2 screws failed at significantly fi cantly higher torques. Conclusion Using 2 screws for DMUSO fixation constructs may provide higher stiffness and maximum failure torque, and antegrade screw constructs may provide more stiffness than retrograde constructs.