When only a C1–C2 arthrodesis is done, we prefer to use a C2 pedicle screw over a C2 pars screw. This is because the pars screw starting hole is more distal and therefore requires more muscle dissection. But, if a C2 pedicle screw is not possible, then we place a C2 pars screw.
A preoperative CT image must be evaluated to determine if this screw is possible. Some patients have a pars that is too small to accept such a screw.
The starting point of the C2 pars screw is 3–4 mm cranial to the C2–C3 facet joint and in the midpoint of the pars mediolaterally.
Place a small burr hole as the starting point for the transarticular screw.
The trajectory is as dorsal as possible without perforating the dorsal cortex of the C2 pars. This is essentially a short transarticular screw.
Tap, measure the length, and place the screw. Typically a unicortical screw that is longer than 16 mm is adequate.