Occipital screws in occipitocervical fusion and their relation to the venous sinuses: an anatomic and radiographic study.

ABSTRACT

This study examined the safe zone for placement of occipital screws without endangering the sinuses. In the first part of the study, 10 cadaveric skulls were exposed. The borders of the confluences and the transverse sinuses were located on the outer table of the occiput. In the second part of the study, six cadaveric skulls were used and screws were placed in different sites and angiography of the venous sinuses was performed. The exact location of the venous sinuses on the outer table of the occiput were analyzed. The examination of the relationship between occipital screws placed at different sites and the venous sinuses clearly demonstrated that whenever the screws were inserted at the level of the external occipital protuberance, or 1 cm below it, sinus injury could rarely be avoided. To enhance the safety of the occipitocervical fusion, the external occipital protuberance should be avoided, and occipital screws should be placed at least 2 cm below the superior nuchal line.