CT analysis of C2 pedicles morphology and considerations of useful parameters for screwing.

Introduction: Surgery of cervical spine steadily requires realizing posterior osteosynthesis. The anchoring of instrumentation in C2 steadily constitutes an important stake of prognosis. Pedicle screwing is one of the best options and remains associated with a low morbidity. The aim of this CT study is to provide, from a wide population, the descriptive anatomical parameters of C2 pedicles. The data enable this analysis of feasibility of C2 pedicles screwing.

Materials And Methods: A continuous and retrospective series have explored 100 CT scans of the cervical spine without finding C2 fracture. The software OSIRIX v5.0.2 has been used. The dimensions of the pedicles in C2 as length, diameter, and distance from the vertebral foramens have been measured from the preset posterior entry point. Their orientation has been described in the axial and sagittal plan by the pedicle transverse angle, the sagittal angle and the pedicle-lamina angle used as a visible mark during the procedure. At least, the feasibility of pedicle screwing has been evaluated using a diameter criterion higher than 4 mm.

Results: The dimensions analysis of 200 studied pedicles has found an average length as 26.18 mm, an average diameter as 5.18 mm and an average distance between the entry point and the vertebral foramen as 9.06 mm. Their orientations have an average PTA as 36.6° and a SA as 25.8°. The average of the PLA was 81.3. The screwing feasibility has been evaluated as 92.5 % in the whole series.

Conclusion: These morphological data come from a large series give some help for the C2 pedicle screwing preoperative planning. These lean on 3D measures but also on accessible mark during the procedure and despite the difference of the patient orientation. A CT preoperative planning of the pedicle screwing remains essential because more than 7 % of the pedicles have a diameter lower than 4 mm.