Are C2 pedicles always screwable? Calibration and planning with a pedicle-lamina angle

Introduction. - Posterior cervical arthrodesis is associated with osteosynthesis. C2 pedicular screwing affords a good bone anchoring but involves neurological and vascular risks. Purpose. - To determine C2 pedicular screwing feasibility from a large cohort of cervical CT scans. To describe the visible anatomical parameters during a surgical procedure in order to plan and secure it. Materials and methods. - Retrospective consecutive series of 100 cervical CT scans was analyzed. Cases with upper cervical fracture were excluded. C2 surgical anatomy was assessed according to maximum length, minimum width and minimum height. Angular parameters were pedicle-transverse angle and sagittal angle. Original pedicle-lamina angle was used as a visible mark during the procedure independent of the patient's position. Pedicular screwing feasibility was evaluated. It was arbitrarily defined by a lower minimum height less than 4 mm. Results. - Two hundred C2 pedicles were analyzed with 7.5% that were not screwable. Their mean length was 26.2 mm, with a mean width of 5.2 mm and a mean height of 9.2 mm. Mean pedicle-transverse angle was 36.2 degrees, mean sagittal angle was 25.8 degrees and mean pedicle-lamina angle was 81.3 degrees. Conclusion. - C2 pedicle screwing feasibility is inconstant due to anatomical variability. In fact, 13% of patients have at least one non-screwable pedicle. Preoperative planning is essential to achieve this procedure. A pedicle-lamina angle can be used which remains independent from the patient's position. (C) 2016 Elsevier Masson SAS. All rights reserved.