Quantitative anatomy of the transverse foramen and pedicle of the axis

Forty dry C2 cervical vertebrae were obtained to evaluate quantitatively the anatomy of the C2 transverse foramen and pedicle. Computed tomography (CT) scans and plain radiographs were also obtained of 20 specimens to evaluate the internal structure of the transverse foramen and pedicle. The results of the measurements showed that differences between male and female specimens were found to be significant for four of seven linear parameters and for one of the two angular parameters. With regard to the sides, differences were found to be significant for two of the seven linear parameters and both of the angular parameters between right and left measurements. The variation of the foramen size between sexes was more significant than that between sides, and a remarkable variation between sides and between sexes was found in the transverse foramen horizontal angle and the pedicle width. The inferior pedicle width was approximately 3 mm less than the superior pedicle width. CT scans revealed that the lateral wall of the pedicle is very thin compared with the medial wall. Considering the greater variation of the C2 foramen orientation, smaller inferior pedicle dimension, and thinner lateral pedicle wall, a screw placement as close as possible to the mediosuperior cortex is recommended to avoid violation of the transverse foramen if transpedicular screw fixation in C2 is intended.