Biomechanical Stability of Diaphyseal Ulnar Shaft Fractures and Ulnar Shortening Osteotomies After Fixation

Background: To determine the amount of micromotion during forearm rotation after diaphyseal ulnar shaft fracture or osteotomy. Methods: This was a biomechanical study using 7 paired-matched cadavers. The upper extremity was mounted in a custom rig and the forearm brought through full pronation and supination. A Hall effect sensor was placed at the fracture ends to measure micromotion for all tested conditions. There were 4 conditions tested: (1) intact ulnar shaft with plate to act as a control; (2) transverse fracture/osteotomy without stabilization; (3) fracture/osteotomy with cortical apposition stabilized with plate fixation; and (4) 50% comminuted fracture stabilized with plate. Results: There was a significantly greater amount of fracture site motion in the fracture/osteotomy model without stabilization compared with all other tested conditions (P <.001,.0001,.0003, respectively). The fracture/osteotomy site with cortical apposition and the comminuted fracture models showed no statistically significant differences in the amount of micromotion compared with each another (P =.952) or compared with the intact ulnar shaft (P =.997,.889, respectively). Conclusions: There was no significant difference in the amount of motion between an intact ulnar shaft, an ulnar shaft fracture with cortical apposition stabilized with a plate, and a plated comminuted fracture. These findings may help surgeons decide on their type of postoperative immobilization in the setting of isolated ulnar shaft fractures or ulnar shaft osteotomies stabilized with plate fixation.