[Digital and anatomical study of posterior atlantooccipital joint-occipital condyle-clivus screw technique].

ABSTRACT

Objective: To investigate the screw placement parameters, feasibility and safety of posterior atlantooccipital joint-occipital condyle-clivus screw technique in Chinese people. Methods: Upper cervical spine CT images of 46 patients, including 24 males and 22 females, were collected with random number table from June 2019 to May 2020 in Ningbo No.6 Hospital. The patients aged 20-55 years, with a mean age of (39±9) years. Total of 92 sides of upper cervical spine models were obtained by Mimics 19.0 digital three-dimensional reconstruction, and screw placement was conducted simulately. The midpoint of transition zone between the posterior arch of atlas and the inferior articular process of lateral mass was selected as the screw entry point. The diameter and length of screws was 3.5 mm and 50 mm, respectively. Detailed morphometric measurements of the 92 atlantooccipital joint-occipital condyle-clivus screws were conducted. The distance between the screw and its surrounding important structures, screw inside and upper tilting angles, the length of screw trajectory in atlas and the length of screw trajectory on occipital side (occipital condyle-clivus) were all measured. Paired t test was performed on the parameters of left and right screw placement to confirm whether there was difference between the two sides. Results: In the 46 cases of upper cervical spine digital three-dimensional models, 92 posterior atlantooccipital joint-occipital condyle-clivus screws were implanted. All the screws were completely fixed in the clivus, without breaking through the upper sphenoid sinus, entering into the canalis spinalis and foramen magnum, and damaging the surrounding structures such as hypoglossal canal. The screw trajectory parameters between the left and right sides were slightly different, but there was no statistical differences between the two sides (P>0.05). The vertical distance between the screw entry point and the upper edge of atlas was (12.6±1.0) mm, the vertical distance between the screw entry point and the lower edge of atlas was (6.5±0.6) mm, the distance between the screw and the medial border of atlas vertebral artery foramen was (6.7±0.6) mm, the distance between the screw entry point and the medial wall of atlas was (6.6±0.7) mm, the distance between the screw outer margin and the hypoglossal canal was (5.5±0.6) mm, screw inside tilting angle was 21.2°±2.5°, screw upper tilting angle was 52.0°±3.4°, the length of screw trajectory in atlas was (12.1±0.9) mm, the length of screw trajectory on occipital side (occipital condyle-clivus) was (37.9±0.9) mm. Conclusion: The posterior atlantooccipital joint-occipital condyle-clivus screw technique can serve as a feasible and safe treatment for instability of the occipitocervical junction, which can be used as a new posterior occipitocervical fusion technique.