Biomechanical stability of coronoid fractures with different fragment heights in the terrible triad of the elbow: CT measurement and finite element analysis.

Background: Coronoid fracture height is an independent factor influencing elbow joint stability. In the terrible triad of the elbow, coronoid fractures are typically manifest as small transverse fractures involving the coronoid tip. Anatomical reduction and stable fixation of the coronoid fragment are therefore critical for restoring concentric reduction and reliable stability of the elbow joint. This study investigated the effect of coronoid fracture fragment height on elbow joint stability under dual parallel Kirschner wire fixation and explored the quantitative relationship among fragment height, stress distribution, and displacement. The findings aim to facilitate a transition in elbow injury management from experience-based treatment toward data-driven precision therapy. Methods: Based on computed tomography data, the coronoid fracture fragment height was measured in 60 patients with the terrible triad of the elbow. Four finite element models representing coronoid fracture heights of 15%, 30%, 45%, and 60% were established. A finite element analysis model was constructed to simulate coronoid fracture fixation using dual parallel Kirschner wires. Pull-out, horizontal, and rotational displacement simulations were performed for each model. Stress distribution within the fixation devices and fracture fragments, as well as fragment displacement, were recorded. Von Mises stress distributions were generated to evaluate the mechanical behavior and stabilizing effect of the fixation construct. Results: Among the four models, the 30% fracture height model demonstrated superior pull-out resistance, followed by the 45% fracture height model. In the horizontal displacement simulation, the 30% fracture height model demonstrated stronger resistance to horizontal displacement, whereas the 45% fracture height model exhibited more favorable stress distribution characteristics. In the rotational displacement simulation, fracture fragment displacement increased progressively with increasing fracture height; however, the displacement in all models remained below 1.00 mm. Conclusion: Under the study conditions, dual parallel K-wire fixation provided effective stabilization when the fracture fragment height ranges from 30% to 45% of the total coronoid height, demonstrating relatively favorable biomechanical stability. This fixation strategy represent a relatively stable surgical option for the management of coronoid fractures associated with the terrible triad of the elbow and provide a biomechanical basis for postoperative rehabilitation and early mobilization. However, clinical decisions should be made in conjunction with the assessment of associated ligamentous injuries, radial head fractures, and overall elbow joint stability.