An anatomical study of the C-2 pedicle.

OBJECT The C-2 pedicle plays an important role regarding screw purchase for spinal fixation. The aim of this study was to measure the C-2 pedicle-related linear and angular parameters. METHODS Seven parameters in 160 C-2 pedicles (80 dry vertebrae) were measured using a Vernier caliper (accurate to 0.1 mm) and goniometer. The Student t-test was used to determine statistical significance. The authors found that the C-2 isthmus (pars interarticularis) and the C-2 pedicle are distinct structures. The C-2 isthmus covers the pedicle. The isthmus is present between the superior and inferior articular processes, and the pedicle is the structure beneath the C-2 isthmus. It connects the lateral mass-inferior articular process to the body of the axis. The heights of the right and the left C-2 pediculoisthmic components (PICs) were 10.3 +/- 1.6 and 9.9 +/- 1.5 mm, respectively. The posterior part of the superior aspect of the PIC was wider than the anterior portion. The widths of the posterosuperior aspect of the PIC were 11.1 +/- 2 and 11 +/- 1.7 mm on the right and left sides, whereas the widths of the anterosuperior aspect of the PIC were 7.9 +/- 1.7 and 8.5 +/- 1.6 mm, respectively. The inferior widths of this component were 6.0 +/- 1.5 and 5.5 +/- 1.3 mm on the right and left side, respectively. The lengths of the component were 28.8 +/- 2.9 mm on the right and 28.8 +/- 3.4 mm on the left side. The PIC exhibits a lateral-to-medial and an inferior-to-superior angle. Its axial angles were 28.4 +/- 2.5 and 28.6 +/- 2.2 degrees on the right and left sides, respectively; its sagittal angles were 18.8 +/- 2.1 and 18.8 +/- 1.7 degrees, respectively. CONCLUSIONS The C-2 pedicle can be seen in the inferior aspect of the vertebra, and it connects posterior vertebral elements (that is, the lateral mass and inferior articular process) to the axial body. The isthmus drapes the pedicle. The authors suggest that this be termed "the pediculoisthmic component."