• Marie-Jacqueline Reisener, Artine Arzani, Ichiro Okano, Stephan N Salzmann, Colleen Rentenberger, John A Carrino, Jennifer Shue, Matthias Pumberger, Andrew A Sama, Frank P Cammisa, Federico P Girardi, and Alexander P Hughes.
• Department of Orthopedic Surgery, Spine Service, Hospital for Special Surgery, New York, NY.
• Spine. 2022 Mar 1; 47 (5): E196E202E196-E202.

Study DesignRetrospective descriptive study.ObjectiveThe aim of this study was to create topographical maps of occipital bone thickness and venous sinus (VS) presence to assess the risks of screw insertion in four commercially available occipital plates.Summary Of Background DataCraniocervical junction instability and deformity are serious pathological conditions that require posterior fixation of the occipital bone to the cervical vertebrae. Insertion of occipital bone screws requires evaluation of both occipital bone thickness for effective internal fixation and intracranial VS presence for vascular injury prevention. Despite the surgical risks, there is a paucity of research on safe screw placement.MethodsWe created a matrix of 231 standardized measurement points to analyze the occipital bone thickness and VS presence in cervical spine CT angiograms. These measurements were used to create topographical maps of occipital bone thickness and likelihood of VS presence, which we then compared to the screw hole configurations of four occipital plates.ResultsHundred patients were assessed. Maximum occipital bone thickness of 13.9 ± 3.3 mm was midline in the occipital bone, 45 mm from the foramen magnum, around the external occipital protuberance (EOP). Regions with thicknesses >8 mm were 2 cm lateral to the EOP at the level of the superior nuchal line and 2.5 cm inferior to the EOP. The area with the highest VS presence rate was around the EOP and the superior nuchal line. The right transverse VS was more prominent in both sexes.ConclusionThere is a limited area of the occipital bone with thicknesses for enough screw purchase. Previous studies have shown 8 mm as the minimum screw length to reduce the risk of implant failure. In our analysis, only "T"-shaped plates had configurations with thicknesses >8 mm for each screw hole. For every screw hole in the analyzed occipital plates, there was a possibility of VS presence ranging from 8% to 33%.Level of Evidence: 5.Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.

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