Relationship between odontoid fracture angle and cervical sagittal balance

BACKGROUND: Fractures can occur in various locations within the odontoid process with differing orientations. However, little is known about what factors contribute to the anterior versus posterior angles/orientation of these fractures. METHODS: We evaluated 74 patients with odontoid fractures (2013–2018) from a single-institution. Patients’ fracture angles/orientations were measured on computed tomography studies, and were grouped into oblique posterior (OP) or oblique anterior (OA) groups. We also took into account cervical sagittal balance utilizing upright x-rays. Other variables studied included patients’ ages, sagittal balance measurements, and the mechanisms of injury. RESULTS: Fracture angles were significantly steeper in the OP group. OP fractures had larger C2-C7 sagittal vertical axis, occiput-C2 angles, and occiput-C7 angles versus anteriorly oriented fractures. In our linear regression model, advanced age and large occiput-C2 angles were predictive of the odontoid fracture angle. Patients who sustained ground-level falls also had significantly steeper fracture angles versus those involved in motor vehicle accidents. CONCLUSION: The odontoid tends to fracture at a steep, posterior angle in elderly patients who demonstrate a large positive sagittal balance when the head is extended following a ground-level falls.