Relative anatomical study of atlanto-occipital joint for posterior transarticular screw fixation

Objective:To explore the entry point,the anchorage point,the optimal angle and length of the screw trajectory for posterior atlanto-occipital transarticular screw fixation.Methods:Anatomic characteristics were observed and measured of dried occipital condyle and atlas specimens.Results:The ideal angle of the atlanto-occipital transarticular screw trajectory was(20.3±2.0)° medial to the sagittal plane and(49.4±2.4)° cephalad to the transverse plane.The optimal length of the screw was(13.94±0.96) mm in the occipital condyle and(12.84±0.62) mm in the atlas.Conclusions:Anatomically,there is a feasibility of using posterior atlanto-occipital transarticular screw fixation.The entry point is in the middle of the junction of the C1 posterior arch and the midpoint of the posterior inferior part of the C1 lateral mass.The strew can be implanted safely in the condition of selecting appropriate length and standard angle of the trajectory.