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

This study examined the safe zone for placement of occipital screws without endangering the sinuses. In the first part of the study, 10 cadaveric skul ls 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 s tudy, six cadaveric skulls were used and screws were placed in different si tes 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 differe nt sites and the venous sinuses clearly demonstrated that whenever the scre ws 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 sup erior nuchal line.