Biomechanical finite element analysis of occipitocervical joint-zonular bone-occipital condyle-screw on the inclined plane

Objective This study aimed to determine the biomechanical stability of C0-C2 vertebrae fixed by atlantooccipital joint-occipital condyle-slope screw fixation (AO-CO-C screws) using finite element analysis. Methods Using computed tomography images, a nonlinear intact three-dimensional C0-2 finite element model (FEM) was developed and validated. Six FEMs were reconstructed: intact model, unstable model, atlantoaxial fusion with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group A), occipital plate screw with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group B), transarticular atlantoaxial screw with C2 pedicle screw fixation finite element model (Group C), occipital-cervical screw with counter-odontoid peg-C2 pedicle screw fixation finite element model (Group D). Range of motion and maximum von Mises stresses were compared under flexion, extension, lateral bending, and axial rotation. Results Group D showed the greatest decrease in ROM(range of motion) with flexion, which was higher than that of the other techniques. The maximal von Mises stress on Group A and Group B showed the occipital condyle screw began contact with the occipital condyle bone, whereas Group C and Group D. Group C had maximal von Mises stress on the atlanto-occipital joint region; the maximal von Mises stress on Group A was located in the area where the occipital condyle screw began contact with the occipital condyle bone, whereas Group C and Group D had maximal von Mises stress on the atlanto-occipital joint region, and the maximal von Mises stress on Group B was located in the area of the bottom of the C1 lateral mass screw. Conclusion In this study, AO-CO-C screws fixation is the most stable technique. If surgeons have to use other fixation methods, they should be aware that additional fixation or postoperative immobilization may be required to achieve ROM restriction. Careful observation at the maximum stress site on the screw, including screw loosening, screw-bone interface disruption, or screw fracture, is necessary during follow-up imaging examinations(X-ray and CT scans)after occipitocervical posterior fixation.