Clinical anatomic study of anterior C_(1～2) transarticular screw fixation

Objective: To provide anatomic data for anterior C1～2 transarticular screw fixation. Methods: Direct measurements were taken from 100 pairs of dried human C1 and C2 vertebrae. The anterior C1～2 transarticular screw insertion point was at the junction of the lateral edge of the C2 vertebral body to 4 mm above the inferior edge of the C2 anterior arch. The parameters related to anterior transarticular atlantoaxial screw fixation were measured. Results: The minimal lateral deflection angle of the screw placement on coronal plane was about (5.5±2.0)°(0°～13.0°), and the maximal lateral deflection angle about (23.6±2.1)°(17.5°～32.5°)on average. The minimal posterior tilt angle of the screw placement on the saggital plane was about (14.9±2.6)°(9.0°～27.0°), and the maximal posterior tilt angle about (25.6±2.5)°(17.5°～33.5°) on average. The length of the medial screw path was about(16.58±1.49)mm(13.78～21.86 mm), and the length of the lateral screw path (26.44±1.75)mm(21.81～33.78 mm)on average. Conclusions: An anterior transarticular atlantoaxial screw with the length of 16-26 mm, the lateral deflection angle of 5°~23° on coronal plane, and posterior tilt angle 15-26° on sigittal plane is safe for inserting.