IMPORTANCE OF THE C1 ANTERIOR TUBERCLE DEPTH AND LATERAL MASS GEOMETRY WHEN PLACING C1 LATERAL MASS SCREWS

Abstract

We measured the variability in the size of the anterior tubercle of C1 and the optimal depth and angle of placement of C1 lateral mass screws using axial and sagittal reconstructed computed tomographic scans to determine the utility of these parameters for preoperative planning and intraoperative guidance. One hundred consecutive cervical spine computed tomographic scans were reviewed (mean patient age, 44.6 years; age range, 7-96 years). The size of the anterior tubercle of C1, bilateral depths of optimal screw placement in the axial and sagittal planes, and optimal angles of placement in the axial and sagittal planes were measured in a standardized manner using the measuring tool included in our radiology server software. These measurements were correlated with age and sex. The mean depth of the C1 tubercle was 6.9 mm (range, 2.7-11.2 mm; standard deviation, 1.7 mm). The depth of the C1 tubercle tended to increase with age, but the relationship was not significant. The optimal screw depth in the sagittal plane was significantly greater than in the axial plane (right 2.09 versus 1.93 cm; left 2.07 versus 1.91 cm). The depth of the right lateral mass increased significantly with age. No other relationships reached significance. The depth of the anterior tubercle of C1 varies considerably and should be studied carefully before using lateral fluoroscopy of this structure to guide depth of C1 lateral mass screw placement. Optimal angles and depths of placement of C1 lateral mass screws vary widely and should be examined preoperatively to plan appropriate depth and trajectory.