The ipsilateral lamina-pedicle angle: can it be used to guide pedicle screw placement in the sub-axial cervical spine?

Pedicle screws in the sub-axial spine are infrequently used because of concerns over their safety and difficulty in placement, despite their superior pullout strength. In the sub-axial cervical vertebrae, we have observed that the lamina appears to project at right angles to the ipsilateral pedicle axis. The aim of this investigation was to confirm the lamina orientation as a reliable landmark for pedicle screw placement. 80 digital cervical spine CT were analysed. The angle formed by the ipsilateral outer lamina cortex to the pedicle axis was recorded. A total of 398 vertebrae were analysed from patients with a mean age of 39.5 years (range 18-78). Average axial lamina-pedicle angle ranged from 96.6 degrees at C3 to 87.2 degrees at C7 in males, and from 95.6 degrees to 87.5 degrees in females. The angle formed by the posterior cortex of the lamina and the ipsilateral pedicle shows a high level of consistency for sub-axial cervical vertebrae ranging from 96 degrees at C3 to 87 degrees at C7. Although the angle is not exactly 90 degrees at all levels as hypothesised, the orientation of the lamina, nevertheless, forms a useful reference plane for insertion of pedicle screws in the sub-axial cervical spine.