Patient 28 year male following RTA presented with rt.upper limb weakness. His MRI and CT spine revealed #c2 dens type 2 with AAD. After CT angio and blood investigation patient planned for c1'2 arthrodesis posteriorly.

His pre and post-op images given below. The question is When we will we use an odontoid screw for c2 #dens? c1, 2 transarticular screws for arthrodesis is used in which sets of patients?