Radiological and anatomical study of posterior occipital condyle screw trajectory

Objective To investigate the optimal trajectory of posterior occipital condyle screw fixation via radiological and anatomical study. Methods Twelve adult craniocervical junction complete specimens were selected. The length, width and height of occipital condyle and the inclination angle of the longest axis were measured by CT scanning and reconstruction. Subsequently, occipital condyle screws were inserted with reference to CT measurements. After screw fixation, accuracy and safety of the placement of occipital condyle screw were verified by gross observation and CT scanning. Results Preoperative measurements of height and width of the occipital condyles indicated the placement of 4. 0 mm bicortical screws was secure. Left vertebral artery horizontal sections of 2 specimens were slightly pressed without damage. CT scanning identified no damage to the inner or outer wall of the occipital condyle and the hypoglossal canal. Trajectory parameters between the right and left sides were slightly different, but no significant difference was observed (P>0. 05). Average screw channel length and inclination angle were (20.8±2.6)mm and (37.1±4.7)°respectively. Angle between screw and skull base tangent was observed as (8.5±1.7)°. Distance between screw axis and hypoglossal canal was observed as (3.1±1.1)mm. And the distance averaged (4.6±1.4)mm between occipital condyle screw entry point and skull base and (6.1±1.5)mm between entry point and inside edge of the occipital condyle. Conclusion Occipital condyle can be used as a new alternative fixed point in occipitocervical fusion. Key words: Occipital bone; Spinal fusion; Occipital condyle screws