Abstract: BACKGROUND: Effective surgical fixation should be performed for patients with ulnar coronoid fractures with unstable elbow joint. When the coronoid fracture fragment is large, there are more internal fixation materials, such as microplates, steel wires, screws, and anchors. However, when the fracture fragment is small, choosing the appropriate internal fixation device is a difficult problem. 
OBJECTIVE: To explore the stability of modified threaded Kirschner wire in the treatment of ulnar coronoid process fracture using finite element analysis.
METHODS:  Thin layer 128-row CT was applied to scan the elbow of one healthy male volunteer. Ulnar coronoid process Regan-Morrey II type fracture model was established using the software such as Mimics 21.0. The models of ordinary Kirschner wire (1.2 mm) and modified threaded Kirschner wire (1.2 mm) were established by Unigraphics NX 10.0 software. The above three kinds of model data were imported into ANSYS Workbench software to generate the ulnar coronoid process Regan-Morrey II type fracture model of ordinary Kirschner wire fixation (ordinary wire group) and the ulnar coronoid process Regan-Morrey II type fracture model of modified threaded Kirschner wire fixation (threaded wire group). The anti-pull-out simulation test, anti-horizontal displacement simulation test and anti-rotational displacement simulation test were carried out for both groups of models. The displacement and stress changes of fracture blocks were recorded, and the variation curves were plotted and Mises stress nephogram was obtained. 
RESULTS AND CONCLUSION: (1) In the anti-pull-out simulation test, the maximum displacement and the maximum stress of the ordinary wire group were 3.96 mm and 93.2 N, respectively. The maximum displacement and the maximum stress of threaded wire group were 0.20 mm and 177.6 N, respectively. The stress distribution of the threaded wire group was slightly more concentrated than that of the ordinary wire group. (2) In the anti-horizontal displacement simulation test, the maximum displacement and the maximum stress of the ordinary wire group were 0.55 mm and 199.2 N, respectively. The maximum displacement and maximum stress of the threaded wire group were 0.05 mm and 573.7 N, respectively. The stress distribution of the threaded wire group was slightly more concentrated than that of the ordinary wire group. (3) In the anti-rotational displacement simulation test, the maximum displacement and the maximum stress of the ordinary wire group were 3.75 mm and 332.2 N, respectively. The maximum displacement and the maximum stress of the threaded wire group were 0.25 mm and 225.6 N, respectively. The stress distribution of the threaded wire group was slightly more concentrated than that of the ordinary wire group. (4) The experiment proves that the modified threaded Kirschner wire has better stability in fixation of ulnar coronoid process fracture. 

Key words: ulna, fracture, ulnar coronoid process fracture, internal fixation, Kirschner wire, finite element analysis