Clinical anatomical study of anterior occiput to axis screw fixation

[Objective]To explore the anatomical basis for clinical applications of occipitocervical fusion by anterior transarticular screw fixation from the axis to the occiput. [Methods]The correlated anatomic linear and the screw rajectory parameters of anterior transarticular screw fixation from the axis to the occiput were observed and measured on thirty adult human bone specimens.According to the data measured,anterior occiput-to-axis screw fixation was performed on the dry craniovertebral junction specimens.Roentgen rays were examined to study the positions of screws and to measure the angle of the screw trajectory. [Results]The occiput to axis transarticular screw trajectory was placed posteriorly tilting in sagittal plane and lateral tilting in coronary plane.The screw tip was located in the posterolateral third of the occipital condyle.There was no significant difference(P0.05) between leftside and rightside.The ideally placed angle of the screw was direct(18.15±3.70) °laterally in the coronal plane and(24.20±4.91) °posteriorly in the sagittal plane.The ideal length of the trajectory was(34.45±2.9) mm.Imageological examination and direct vision demonstrated that anterior occiput to axis screw fixation according the above results ensured insertion of the trajectory passing through the atlanto-occipital articulation and the atlanto-axial articulation without piercing the bones. [Conclusion]From the anatomical standpoint,the technique of anterior fixation from the atlas to the occiput is feasible.