Finite element modelling of posterior occiput-axis fixation and biomechanical analysis of C2 intralaminar screw fixation with offset connectors.

The occiput-axis crossing translaminar screw (C2LAM) fixation technique can help avoid vertebral injury, while the inclusion of offset connectors can facilitate implantation. This three-dimensional finite element (FE) study compared the stability of C2LAM using offset connectors (C2LAM + OF) with other methods. Occipital and cervical spine computed tomography images of a healthy 30-year-old man were selected to build the FE model. Four internal fixation instruments including occiput plate-C2 pedicle (C2P) and pars (C2Pars) screws, as well as C2LAM and C2LAM + OF were applied consecutively to the model respectively to establish four new models, which were subjected to all states of motion and physiological loads to simulate normal movement, including the four kinds of basic activities of human such as flexion, extension, lateral bending, and axial rotation. Physiological measures and comparison included the range of motion (ROM) and stress distribution in the model. ROM between the fixation techniques was comparable, and the stability of the C2LAM + OF fixation technique was similar to that of C2P. Screw entry points, offset connectors and rods were the main stress distribution regions in the C2LAM + OF system. The mean von Mises stress of the inner wall was significantly smaller than that of the outer wall in flexion, extension, and rotation (p < 0.05); however, lateral bending was comparable, indicating a relatively small risk of damage to the inner wall. The results of this study indicate that the C2LAM + OF fusion technique can provide sufficient stability and can be used as an alternative to C2P under special circumstances.