Anatomical Study Of Anteriror Approach Screw Fixation Through C2 Vertebral Body Into C1 Lateral Mass

Objective Measurement of the anatomical study of anterior approach screwfixation through C2 vertebral body into C1 lateral mass by CT was performed toprovide anatomical basement for the clinical operations and confirm theoperations whether safe and security, and contrast the two operations with differentapproach.Methods 40 normal patients (20 male, 20 female) underwent sprial CT of thecervical spine which were transferred to the workstation in order to reconstructmulti-planar reconsturction(MPR). The screw tragectory wer imitated by linesdirection. Some parameters of the two operations with different entry point(1: C2vertebral body inferior midpoit; 2; the inferior midpoint of the atlantoaxialtransarticular facet)include the maximal lateral angulation, the minimal lateralangulation, the maximal posterior angulation and the minimal posteriorangulation, the lenth of the imitated screw, the lengh between the entry point andthe midline.Resuls Entry point: C2 vertebral body inferior midpoint: the maximal lateralangulatio is 36.2°±2.26°, the minimal lateral angulation is 28.0°±1.9°, theidal lateral angulation is 31.9°±1.6°, the maximal posterior angulation is 25.2°±2.1°, the minimal posterior angulation is15.6°±2.2°, the ideal posteriorangulation is 20.3°±1.7°, the ideal screw trajectory lenth is 5.4cm±0.1cm Entry point: the inferior midpoint of the atlantoaxial transarticular facet.the maximal lateral angulation is 29.9°±2.6°, the minimal lateral angulation is 12.5°±2.7°, the idal lateral angulation is 21.3°±2.1°, the maximal posterior angulation is 40.5°±2.3°, the minimal posterior angulation is 9.3°±2.6°, the ideal posterior angulation is24.4°±2.8°the ideal screw trajectory lenth is 2.7cm±0.1cmThe distance between the inner-most atlantoaxial transarticular facet and theinner-most vertebral artery cannal is 1.4±0.1 cm, the distance between theinferior midpoint of the atlantoaxial transarticular facet and the midline of the C2vertebral body is 1.0±0.1 cmConclusions: When the entry point is C2 vertebral body inferior midpoint, thelateral angulation is about 35°, the posterior angulation is 20°, the screwtrajectory lenth is 5～5.5cm. When the entry point is the inferior midpoint of thelatlantoaxial transarticular facet, the lateral angulation is about 20°, the posteriorangulation is 25°, the screw trajectory lenth is about 2.7cm. In clinical use we willreduce the complications and risks and improve the accuracies of the operations ifwe are familiar to the atlantoaxial anatomy and use X-ray in the operations.