To verify the feasibility of using modified half-thread Kirschner wire in the treatment of ulna coronoid process fracture through mechanical mechanics, biomechanics and animal experiments, and to provide a new internal fixator for clinical use.

The modified half-thread Kirschner wire with diameter of 1.5 mm, ordinary Kirschner wire with diameter of 1.5 mm and ordinary Kirschner wire with diameter of 1.2 mm were set as group A, B and C. The mechanical properties of the modified half-thread Kirschner wire were tested by mechanical experiments (tension, bending and torsion) with a universal testing machine. The stability of fracture block fixed with modified half-thread Kirschner wire was tested by anti-pullout test. The animal experiments were conducted to observe whether the modified half-thread Kirschner wire was loose, broken and the screw teeth fell off during removal.

In the tensile test, there were significant differences in the maximum tensile load and displacement between group A, B and C (F_{tensile load}=1166.015, F_{tensile displacement}=168.931, P<0.001). The differences between group A and B, group A and C were still statistically significant (P_{A vs B}<0.001, P_{A vs C}<0.001). In the bending experiment, there was significant difference in the maximum bending load between the three groups (F= 495.758, P=0.001). The differences between group A and B, group A and C were still statistically significant (P_{A vs B}<0.001, P_{A vs C}<0.001). However, there was no significant difference in the mean maximum bending displacement between the three groups (F=0.214, P=0.809). In the torsion experiment, there were significant differences in the maximum torsion load and angle among the three groups (F_{torsion load}=174.216, F_{torsion angle}=516.322, P<0.001). The differences between group A and B, group A and C were still statistically significant (P_{A vs B}<0.001, P_{A vs C}<0.001). In the pull-out test, there were significant differences in average maximum load and displacement between groups A and B (t_load=74.403, t_displacement=7.445, P<0.001). In the animal experiment, when the Kirschner wire was taken out after the fracture healed, no loosening, broken needle and screw tooth falling off were found.

The ordinary Kirschner wire with a diameter of 1.5 mm is an modified half-thread Kirschner wire after adding the thread design. Its mechanical properties can still meet the requirements of clinical application, and its holding force on the fracture block is significantly better than that of the ordinary Kirschner wire with the same diameter. Its application in the treatment of ulna coronoid process fracture is highly feasible, with the advantages of good stability, simple operation and early rehabilitation.

Internal fixators; Biomechanics; Animal experimentation; Ulna fractures; Modified half-thread Kirschner wire