Anatomy of atlanto-occipital joint for posterior transarticular screw fixation

Objective: To study the anatomic data of the occipitoatlantoaxial complex of Chinese so as to provide anatomic clues and confirm feasibility of posterior occipitoatlantoaxial transarticular screw fixation. Methods: Anatomic data were obtained by measuring the dried occipital condyle and atlas specimens from normal Chinese adult cadavers, and anatomic observation was conducted on the posterior occipitoatlantoaxial complex from fresh human cadaveric occipitocervical specimens. Results: The articular face of the occipital condyle was inside oblique. The distance between the articular face of occipital condyle and the hypoglossal cannal was 9.66 mm±1.13 mm; the distance of the angle of the 2 occipital condyles was 14.93 mm± 1.84 mm; the inside oblique angle of articular face of occipital condyle was (left) 12.5°±2.6° and (right) 11.6°±3.7°. The anteroposterior and lateral diameter of the articular face of occipital condyle, the anteroposterior and lateral diameters of the superior articular facet of atlas, and the width of the lateral mass in the cross of posterior arch and lateral mass were all larger than 5 mm. The vertebral artery tranveled constantly along the vertebral arterial sulcus. C1 and C2 dorsal roots did not cross the atlans inferior facet and they were movable to a certain extent. Conclusion: Anatomically, there is a feasibility of using posterior atlanto-occipital transarticular fixation; the ideal entry point is at the central point where posterior arch of atlas migrate to the inferior articular process, and the screw directs to the anterosuperior part of the occipital condyle.