Traumatic posterior atlantoaxial dislocation based on imaging of the anterior arch-odontoid process-transverse ligament complex: a retrospective cohort study.

Abstract

Traumatic posterior atlantoaxial dislocation (TPAD) is uncommon, and related research is very limited. By analyzing the imaging characteristics of the anterior arch-odontoid process-transverse ligament complex in patients, the authors classify the outcomes of TPAD and elucidate its mechanisms of injury. This is a retrospective review of CT and MRI data on patients with TPAD treated at two clinical centers from June 2014 to March 2024. Through analysis and statistics on injuries to the anterior arch, odontoid process, and transverse ligament complex, the authors proposed a new classification method based on different injuries to these structures on imaging. Additionally, they discuss the role of hyperflexion and hyperextension injuries in the formation of TPAD. The different injuries to the anterior arch-odontoid process-transverse ligament complex on imaging were classified into four types of TPAD: fracture-free TPAD (type I), odontoid process fracture TPAD (type II), anterior arch fracture TPAD (type III), and compound fracture TPAD (type IV); the latter three types are referred to as "fracture-associated TPAD." Considering the significant role of the transverse ligament in injuries, these four fracture types were further divided into two subtypes based on transverse ligament integrity (i.e., intact or injured). Among the 41 patients included in the study, there were 2 cases of fracture-free TPAD (i.e., 1 type Ia case and 1 type Ib case) and 39 cases of fracture-associated TPAD (i.e., 31 cases of odontoid process fracture TPAD, including 18 type IIa cases and 3 type IIb cases; 5 cases of anterior arch fracture TPAD, including 3 type IIIa cases and 2 type IIIb cases; and 3 cases of compound fracture TPAD, including 2 type IVa cases and 1 type IVb case). Based on the imaging classification method for different injuries to the anterior arch-odontoid process-transverse ligament complex, TPAD injuries demonstrate a higher degree of alignment, facilitating a comprehensive understanding of these injuries. Hyperflexion and hyperextension are the primary mechanisms in TPAD injuries, with the integrity of the transverse ligament playing a crucial role and guiding treatment principles.