An applied anatomic study of investigating the inserting position that placement of screws in the Chinese occipital condyle

Objective To investigate the choice of screw placement in the Chinese occipital condyle using applied anatomy and imaging.Methods Twenty heads of fresh cadavers were chosen for the study.First,computerized tomography (CT) scanning and two-dimensional (2D) reconstruction were performed on these heads,aiming to exclude the heads with destroyed or deformed occipital condyle.In the CT imaging,4.0 mm virtual lines were used to simulate the process of inserting screws.Using the longest diameter of the head in sagittal plane as the standard,the position of inserting screws was chosen,and the horizontal distance between the position of inserting screws and the margin medialis of the occipital condyle,and the vertical distance between the position of inserting screws and the basis crania were measured.Based on the result of measurements,the position of inserting screws was determined.After removal of partially posterior arch of the arlas,4.0 mm screws were inserted.According to the anatomy of the occipital condyle,vertebral artery filling experiments and CT testing,the results of the position of inserting screws were examined.Results Twenty fresh body heads met the criteria of CT examinations,and 40 complete occipital condyles were chosen.According to the position of inserting screws measured by CT,screws were successfully inserted in 36 of the 40 occipital condyles.Anatomy and postoperative CT scanning demonstrated that the hypoglossal canal was not damaged,and the screws did not pierce the inner or outer side wall of the occipital condyle.The vertebral artery was not damaged in all heads.However,4 crews pierced the inner side wall of the occipital condyle.The horizontal distances between the position of inserting screws and the margin medialis of the occipital condyle were (7.6±0.9) mm (left) and (7.3±0.6) mm (right),respectively,and there was no significant difference between them.The vertical distances between the position of inserting screws and the basis crania were (10.2±1.6) mm (left) and (9.9±1.0) mm (right),respectively,and there was no significant difference between them.Conclusion The choice of accurate position of inserting screws based on the CT reconstruction could make the longest length of inserting screws,and reduce the risk of inserting screws as much as possible.There was no significant difference between the right and left sides in the position of inserting screws in the occipital condyle.Removal of partially posterior arch of the atlas could effectively protect the vertebral artery. Key words: Occipital bone;  Bone screws;  Anatomy, regional