LAUSR

The primary aim of this paper is to introduce Quantitative 3-dimensional Computed Tomography (Q3DCT) for odontoid fractures to assess if fracture characteristics differ between the Anderson and d'Alonso subclasses. Secondarily, we assessed if high energy injury and older age influenced fracture morphology. This retrospective imaging study includes 66 patients who visited one of two level I trauma centers for an odontoid fracture. With the use of 3-Dimensional polygon mesh models we determined the total number of fragments, the volume of each fragment, the degree of displacement of the odontoid, and the fracture surface area. We found that type III fractures consisted of more fracture fragments (median:3, IQR:2-3) than type II odontoid fractures (median:2, IQR:2-3) (p < 0.001). The volume of the odontoid fracture fragment was almost twice as large in type III odontoid fractures (median:19%, IQR:14-25%) as compared to type II fractures (median:10%, IQR:8.5-12%) (p < 0.001). Type II fractures were more displaced (median:3.8 mm, IQR:2.9-6.3 mm) compared to type III fractures (median:2.2 mm, IQR:1.0-3.5 mm) (p < 0.001). This 3-dimensional displacement was predominantly due to substantially more posterior displacement of type II odontoid fractures. In conclusion, type III odontoid fractures were more comminuted, had a larger odontoid fragment, had a larger fracture surface, but were less (posteriorly) displaced when compared to type II fractures. The mechanism of injury and age at diagnosis both dictated the fracture type, but when accounting for fracture type the influence of these two factors on fracture morphology was limited.