ANATOMIC CONSIDERATION OF C2 PEDICLE SCREW PLACEMENT

Study Design. This anatomic study tested placement of C2 pedicle screw s using cadaver specimens. Objectives. To further assess the safety of transpedicular screw placement in the axis by comparing two surgical techniques. Summary of Background Data. Transpedicular screw fixation of traumatic spondylolisthesis of the axis has been described in the l iterature. Recently, anatomic studies and clinical applications of tra nspedicular screw fixation for traumatic lesions of middle and lower c ervical spine have been described. No previous study assessing the saf ety of C2 pedicle screw placement is available. Methods. Sixteen embal med cadaveric specimens were used for this study. In the first eight s pecimens (Method A), the point of entry for screw placement was chosen to be about 5 mm inferior to the superior border of C2 lamina and 7 m m lateral to the lateral border of the spinal canal. The screw directi on was chosen to be about 30 degrees medial to the sagittal plane and 20 degrees cephalad to the transverse plane. A 3.5-mm cortical screw o f appropriate length, determined with depth gauge, was placed bilatera lly into the C2 pedicle. In the next eight specimens (Method B), the d irection of the drill bit was guided directly by the medial and superi or aspect of the individual C2 pedicle. Gross dissection was done to v iew violation of dura, nerve roots, vertebral artery, and penetration of medial, lateral, superior, and inferior cortex of the C2 pedicle. R adiographs and computed tomography scans were obtained to evaluate scr ew placement in the C2 pedicle. Results. In Method A, four screws had lateral violations into the vertebral artery. In Method B, only two ca ses of minimal penetration of pedicle cortex were found. No medial, su perior, or inferior violation of the pedicle cortex was found in the p resent study. Conclusions. The present anatomic study suggests that tr anspedicular screw fixation may be performed safely in the C2 pedicle by using the second technique. Using the first technique is not safe.