Computed tomographic morphometric analysis of lateral inclination C1 pedicle screw for atlantoaxial instability patients with a narrow C1 posterior arch

Abstract

Atlanto‐axial instability (AAI) is a congenital or developmental condition that leads to instability/subluxation of the atlantoaxial joint. This study is performed to determine anatomic feasibility of trajectory L and help select an optimal screw trajectory in treating patients with AAI with a narrow C1 posterior arch. Sixty patients who underwent cervical three dimensional‐computed tomography (3D‐CT) were chosen from the hospital's picture archiving and communication system (PACS). Aquilion Multi 64 helical CT was used to perform CT examinations and measurements on patients. Based on CT images, the trajectory L and M for each C1 pedicle were established. Posterior arch height was measured on C1 coronal image. The medullary cavity width along trajectory M was narrower than trajectory L. The medullary cavity width that was less than 3.5 mm was found in 12.5% pedicles along trajectory M and 2.5% along trajectory L. The posterior arch height along trajectory L was significantly higher than that of trajectory M. Posterior arch height that was less than 3.5 mm was found in 74.2% pedicles along trajectory M and only 16.7% along trajectory L. The pedicle length along trajectory L was significantly longer than trajectory M. Trajectory angles for C1 pedicles had an average of 9.08° ± 4.66° along trajectory L and 14.53° ± 4.03° along trajectory M. The Optimal entry point of trajectory L was 5.4 mm medial to trajectory M. Based on our results, this study suggests that C1 pedicle screw trajectory with lateral inclination yielded a good outcome in the treatment of AAI.

Posterior Fusion for the Subaxial Cervical Spine: A Review of the Major Techniques

“…This poses a risk of serious adverse events, such as vertebral artery perforation through the lateral wall and spinal cord injury through the medial wall. With such high medial angulation at more cranial levels, one must expose far laterally, which is sometimes not possible in patients with an anomalous vertebral artery at the C2 level [36] or in those with a narrow C1 posterior arch [56].…”

Biomechanical Effects of Lateral Inclination C1 and C2 Pedicle Screws on Atlantoaxial Fixation

“…Meanwhile, a lateral inclination approach has been signified to improve the safety of the surgery and minimize the screw perforation, and provide more pullout strength and better biomechanical stability; for instance, published data have established that when compared to a medial inclination screw trajectory, C 1 pedicle screw trajectory with lateral inclination can bring about a good outcome in the treatment of atlantoaxial unstableness since it induces a wider medullary cavity width, a higher posterior arch height and lateral mass height, as well as a longer pedicle length 22 . The C 1 posterior arch screw method has been applied in C 1 rigid balanced immobilization 23 , 24 , 25 owing to the numerous advantages which include: (i) high fusion percentage and lower complication ratio; and (ii) less bleeding at venous plexus and soreness of the C 2 roots of the nerve 26 , 27 .…”