Radiological And Anatomical Study Of Posterior Occipital Condyle Screw Trajectory

Objective: To investigate the ideal trajectory parameters of Chinese people’s posterioroccipital condyle screws, and to analysis and verify the accuracy and safety of intraoperativeoccipital condyle screw placement by preoperative CT reconstruction measurement. Methods:12adult craniocervical junction (C0~C2) complete specimens preserved by formalin solution wererandomly selected. Firstly, CT scanning and reconstruction were performed. Then, the length,width and height of occipital condyle and the inclination angle of the longest axis were measured.Subsequently, occipital condyle screws were inserted with reference to CT measurements. Afterscrew fixation, to verify the accuracy and safety of the placement of occipital condyle screw bygross observation and CT scanning. Results: There were no significant differences between the leftand right condyles as it relates to the measured parameters (P>0.05). And, the study found that theheight and width of the occipital condyles easily allow the placement of3.5mm or4.0mmbicortical screws (Medtronic Sofamor Danek). In this study, a total of244.0-mm screws wereinserted into the occipital condyles. The left vertebral artery horizontal sections of2of12specimens were slightly pressed by gross observation without no damage. CT scanning did not findthat the screws pierced the inner or outer side wall of the occipital condyle and that the hypoglossalcanal was damaged. The trajectory parameters between the right and left sides were slightlydifferent, but no significant difference was observed （P＞0.05）. The average screw channellength and inclination angle were respectively (20.76±2.56) mm and (37.13±4.69)°. The anglebetween the screw and skull base tangent was observed as (8.49±1.72)°. The distance betweenthe screw axis and the hypoglossal canal was observed as (3.06±1.05) mm. And the distancesaveraged (4.63±1.37) mm between the occipital condyle screw entry point and the skull base and(6.12±1.49) mm between the entry point and the inside edge of the occipital condyle.Conclusions: In our study, the height and width of the occipital condyles easily allow theplacement of3.5mm or4.0mm bicortical screws. So the occipital condyle can be used as a newalternative fixed point in occipitocervical fusion. Pre-operative CT scanning, reconstruction and themeasurement of related parameters may play an extremely important significance for the accuracyand safety of the placement of intra-operative occipital condyle screws.