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Craniocervical dissociation spectrum injuries (CDSI) represent a spectrum of increasing hyperflexion-hyperextension forces applied to the osteoligamentous structures of the craniocervical junction (CCJ) that may range in severity from isolated craniocervical ligament tears to overt atlanto-occipital dislocation (AOD) [1,2]. Strictly defined, these injuries imply focal trauma between the structures responsible for maintaining integrity between the central skull base and C1-C2, namely, the atlanto-occipital joint, the major CCJ ligaments (capsular ligaments, alar ligaments, and tectorial membrane {TM}), the minor CCJ ligaments (anterior and posterior atlanto-occipital membranes), and the surrounding neck musculature (longus capitis muscle, obliquus capitis superior and inferior muscles, and rectus capitis posterior major and minor muscles). Additional named ligaments, including the apical ligament (vestigial notochordal remnant between the basion of the clivus and the C2 dens), the transverse occipital ligament, the accessory atlantoaxial ligament, and the superior band of the cruciform ligament, are not routinely visualized on cervical magnetic resonance imaging (MRI) and thought to play a nominal role in craniocervical stability [3,4].

The stabilizing structures of the CCJ proper are anatomically and physiologically distinct from the major stabilizing structure at C1-C2. In contrast to the other osteoligamentous CCJ structures, the transverse atlantal ligament (TAL) extends horizontally between the medial tubercles of the C1 lateral masses, extending posterior to the C2 dens, and locks the median atlantoaxial joint in place [5]. There is no direct attachment between the TAL and the skull base. Biomechanical cadaveric studies have demonstrated the unique functional role of the TAL as both a primary stabilizer of the atlantoaxial joint and a primary facilitator of atlantoaxial rotation at C1-C2 [6,7]. Secondary atlantoaxial stabilizers including the lateral atlantoaxial joints, the anterior atlanto-occipital membrane complex (AAOMc), and the longus capitis muscle also support the atlantoaxial joint.

The complex interplay between the craniocervical junction, including the atlanto-occipital joint and its surrounding supportive ligaments and muscles, and the atlantoaxial joint with its strong, stabilizing transverse atlantal ligament is not well understood. Unstable traumatic injuries of the atlanto-occipital and atlantoaxial joint often occur in isolation [8]. Regardless, the conventional teaching of the CCJ anatomy and biomechanics includes the atlantoaxial joint with the CCJ proper, although the anatomy, biomechanics, and traumatic injuries that occur between these two osteoligamentous structures are quite different. The neurosurgical literature regarding the clinical management of CDSI includes conflicting data on the appropriateness of occipital cervical fusion and fusion length/level versus prolonged external immobilization. While occipital cervical fusion is necessary for overt atlanto-occipital dislocation, craniocervical injuries with intact atlanto-occipital joints may be treated with prolonged external immobilization. In contrast, atlantoaxial instability (AAI) is typically treated with operatively via posterior C1-C2 fusion or anterior C1 osteosynthesis [9]. The challenge is the appropriate balance between preserving function and the range of motion with the risk of persistent instability and spinal cord injury. The confusion partly stems from whether CCJ instability involves the atlanto-occipital joint, the atlantoaxial joint, or both. The lack of consensus regarding the neurosurgical management of CDSI is complicated by the high morbidity and mortality of these injuries, which often limits operative management. The incomplete understanding of the association between CDSI and atlantoaxial instability (AAI) injuries on cervical MRI in the radiology literature may also play a role [10-12].

Therefore, the purpose of our study is to identify adult trauma patients with a confirmed acute, post-traumatic tear of the transverse atlantal ligament on cervical MRI and evaluate for concomitant craniocervical junction ligamentous injuries. We hypothesize that atlantoaxial instability more commonly occurs in isolation from atlanto-occipital instability on cervical MRI. A thorough understanding and discussion of the complex interplay between instability at the CCJ proper and the atlantoaxial joint may allow for improved consensus regarding operative management of these injuries.

A waiver of informed consent was granted by the institutional review board (IRB) chairman to retrospectively evaluate the imaging and clinical findings of adult trauma patients (>18 years old) with TAL injuries. Thirty patients who presented to the emergency department (ED) with an intrasubstance tear of the TAL on cervical MRI were identified retrospectively by using the keywords “transverse ligament,” “transverse band,” “cruciform ligament,” or “transverse atlantal ligament” included in cervical MRI reports between January 2015 and January 2021 using Nuance mPower (Nuance Communications, Burlington, MA) software. As a level I trauma center and tertiary care trauma spine center that captures all high-speed motor vehicle accidents (MVA) for a large geographic region, we were able to perform an analytic search of more than 15,000 cervical MRI examinations that presented to the ED for trauma during this time frame. The evaluation of the major and minor CCJ ligaments was performed, including the evaluation of the atlanto-occipital capsular ligaments, alar ligaments, tectorial membrane, and anterior and posterior atlanto-occipital membranes. Bony fractures of the craniocervical junction on preceding cervical spine computed tomography (CT) in addition...(More)

For more info please read, Interrelationship Between Craniocervical Dissociation Spectrum Injuries and Atlantoaxial Instability on Trauma Cervical MRI Examinations, by Cureus