Abstract: Objectives 　To determine the biomechanical differences between C2 pedicle screw and bicortical C2 laminar screw with intra-articular Cage in C1~2 fixation by finite element analysis. 　Methods   A validated three-dimensional finite element model of the upper cervical spine (C0~2) was established, and an unstable model was also established after removing the transverse ligament. Two different implanted models: C1 lateral mass screws+Cage+C2 pedicle screw (C1L+Cage+C2P) and C1 lateral mass screws+Cage+bicortical C2 laminar screw (C1L+Cage+BC2L) were integrated at the C1~2 segment into the unstable model. To study the biomechanics, vertical load of 40 N was applied in the inferior direction on the occipital condyles, to simulate head weight and 1.5 Nm torque was applied to the occiput to simulate flexion, extension, lateral bending, and rotation.　Results　There was no significant difference in the range of motion between C1L+Cage+BC2L and C1L+Cage+C2P implanted models ( <0.1° for all loading cases)，and also there was no significant difference in stress distribution and maximum stress between the 2 implanted models. Bone graft stress of the 2 implanted models, especially the C1L+Cage+C2P fixation model, were minimum under extension loading condition. 　Conclusions 　Our results indicate that the C1L+Cage+BC2L fixation offers similar stability to C1L+Cage+C2P for the treatment of basilar invagination. Compared to C2P technique, the BC2L is an easy, effective technique and it can avoid vertebral artery and spinal cord injury. To avoid the instrumentation failure and stress shelter, neck extension movement should be restricted or banned after surgery.

Key words: Modified Goel technique, 　C2 pedicle screw, 　Bicortical C2 laminar screw, 　Basilar invagination, 　Finite element analysis