Anatomic considerations for the placement of C2 laminar screws

Study Design. Cadaveric study. Objective. To study the applicability of C2 laminar screw placement in the general adult population and to provide useful guidelines for their safe placement. Summary of Background Data. Laminar screws for fixation into the second cervical vertebra are becoming an increasingly used technique since they eliminate the risk of vertebral artery injury. Although it is being used clinically, there are no published data that describe the anatomic considerations and potential limitations of this technique in the general population. Methods. The C2 vertebrae of 420 adult specimens were studied. Laminar thickness, spinolaminar angle, and the length from the spinolaminar junction to the contralateral lamina/lateral mass junction were measured. Statistical analysis was performed using unpaired Student t tests and regression analysis (P < 0.05). Results. Mean laminar thickness was 5.77 +/- 1.31 mm; 70.6% of specimens had a laminar thickness >= 5 mm; 92.6% had a thickness >= 4.0 mm. The spinolaminar angle was 48.59 degrees +/- 5.42 degrees. The mean screw length that could be used was 2.46 +/- 0.23 cm. More than 99% of specimens had an estimated screw length of at least 20 mm. Gender had a significant effect on all of the measurements studied, but race, height, and weight did not. Conclusion. The majority of specimens can safely accept placement of a laminar screw. This study establishes anatomic guidelines to allow for accurate screw selection and insertion. Preoperative planning is essential for safe screw placement via this technique.