Transpedicular screw placement evaluated by axial computed tomography of the lower cervical pedicle

Objective To provide a safe transpedicular screw trajectory by measuring the dimensions of the lower cervical pedicle and evaluating the entrance points and the insertion angles of transpedicular screws.Methods The dimensions of the pedicles(C3-C7) were determined in 60 patients with cervical spinal lesions from CT images.Change of pathology of cervical vertebra was excluded.CT scanning on cervical vertebra was performed in 60 patients with the range of C2-T1,electric pressure was 140 kV,200-250 mA,and depth of cross section was 3 mm.CT images in which each pedicle appeared largest were selected and the following dimensions determined:pedicle inner and outer widths,medial cortical thickness,pedicle axis length,projected length of the pedicle axis and the pedicle transverse angle.Results The mean inner pedicle width ranged from 1.3 to 3.3 mm,the mean outer pedicl width ranged from 4.0 to 7.0 mm.The smallest pedicle width was found at C3 among the female subjects for both inner and outer pedicles,The smallest outer pedicle width was 3.2 mm,the largtest pedicle width was at C7 in both males(11.1mm)and females(7.4mm).The mean medial cortical thickness range from 1.5 to 2.0 mm.The pedicle axis length ranged from 29.3 to 33.7 mm.The mean pedicle transverse angle ranged from 40.6° to 49.6°.Conclusion Axial CT measurements should facilitate transpedicular screw fixation in the lower cervical spine.We believe that the screw insertion angle should be close to 50 degrees,which is the mean pedicle transverse angle from C3-C6.The entry point of the pedicle screw should be located as laterally as possible in the posterior surface of the lateral mass.