When only a C1 – C2 arthordesis 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 3-4mm cranial to the C2-C3 facet joint and in the midpoint of the pars medio laterally.
Place a small burr hole as the starting point for the trans articular screw.
The trajectory is as dorsal as possible without perforating the dorsal cortex of the C2 pars. This is essentially a short trans articular screw.
Tap, measure the length, and place the screw. Typically a unicortical screw that is longer than 16 mm is adequate.