MORPHOLOGY OF THE 2ND CERVICAL VERTEBRA AND THE POSTERIOR PROJECTION OF THE C2 PEDICLE AXIS

Study Design. This study assessed numerous structural features of the second cervical vertebra (C2), describing the projection point of the pedicle on its posterior aspect. Objectives. Evaluation of the specime ns included quantitative description of 18 linear and four angular par ameters, which then were correlated male and female specimens. The poi nt of projection of the C2 pedicle axis was described with an emphasis on a perspective relevant to a posterior approach. Summary of Backgro und Data. The literature regarding the anatomy of the axis focuses mai nly on the dens. Very little research regarding the quantitative study of the C2 pedicle has been reported. Methods. Fifty dry C2 cervical v ertebrae (30 male, 20 female) were obtained for anatomic measurements. Anatomic evaluation focused on the pedicle, vertebral body, dens, sup erior facet, and vertebral canal. All measurements were made using cal ipers and a standard rule linear measurements and a goniometer for ang ular measures. Based on the measurement of 50 specimens, including 18 linear and four angular parameters, the mean, rang, and standard devia tion were calculated for all of the specimens and for male and female separately. Results. A significant difference was found to exist for 1 1 of 18 linear measurements and one of four angular parameters. The pr ojection point of the pedicle axis on the posterior aspect of the late ral mass was described with an emphasis on a perspective relevant to a posterior surgical approach. The location of the projection point of the pedicle axis was found to be 5.4 +/- 1.2 mm inferior to the horizo ntal line, and 7.2 +/- 1.3 mm lateral to the vertical line. The pedicl e axis was found to lie at 33 degrees in the medial direction and 20 d egrees in the superior direction form the point of pedicle axis projec tion. Conclusions. When the techniques described here are used, the fi ndings may be helpful in cases involving C2 when surgical intervention and instrumentation are desired.