Contribution of ligaments to intersegmental stability following type II odontoid fracture

Purpose: Management of Anderson and D'Alonzo type II odontoid fractures continues to be controversial despite extensive research and increasing prevalence. To the authors' knowledge, the three odontoid ligaments, the alar ligament, the vertical portion of the cruciate ligament, and the transverse ligament, have not been biomechanically examined in type II odontoid fracture in spite of their potential significance in management. Therefore, this study aims to explore the intersegmental rotations of the craniovertebral junction following Anderson and D'Alonzo type II odontoid fracture and various combinations of ligament ruptures. Methods: A validated C0-C7 cervical spine finite element model was employed to address the research objectives. The model was subjected to flexion-extension, lateral bending, and axial rotation under eight distinct injury conditions apart from the intact state. Prescribed rotations were applied to the top of the cranium while the C7 inferior surface was fixed. Rotation-moment data were retrieved from the model. Results: Type II odontoid fracture caused mixed forms of instability considering flexion-extension. In lateral bending, the fracture alone did not have a significant effect, whereas the disruption of ligaments led to moderate rotation increments. Notably, in axial rotation, the fracture was the most crucial factor for stability. Conclusions: Overall, type II odontoid fracture was found to be the main destabilizing element. Nonetheless, the vertical cruciate and the transverse ligament played a modest role in stabilization. The alar ligament provided minimal or no stability. Furthermore, instances were observed where both the vertical cruciate and the transverse ligament were necessary to prevent more instability.