Biomechanical analysis of atlantoaxial intraarticular fusion cages with posterior pedicle screws fixation using finite element method.

Background: Cadaveric biomechanical studies indicated that atlantoaxial intraarticular fusion cages with posterior pedicle screws fixation could increase the multi-axial rigidity. However, the stress distribution of the fixation construct is still unclear.

Methods: From computed tomography images, a nonlinear intact three-dimensional C0-2 finite element model was developed and validated. Four finite element models were reconstructed: intact model, unstable model, bilateral atlantoaxial pedicle screws combined bilateral cages model, bilateral atlantoaxial pedicle screws model. The range of motion and maximum von Mises stresses were compared under flexion, extension, lateral bending, and axial rotation.

Findings: Compared with unstable model, both bilateral atlantoaxial pedicle screws combined bilateral cages model and bilateral atlantoaxial pedicle screws model fixation techniques reduced range of motion by >99% in extension, flexion, lateral bending and axial rotation. For bilateral atlantoaxial pedicle screws combined bilateral cages model, the maximum von Mises stress was in the base of the C2 screw head site. In the bilateral atlantoaxial pedicle screws model was stressed at the rod linked C1 and C2 screws. Compared with bilateral atlantoaxial pedicle screws model, bilateral atlantoaxial pedicle screws combined bilateral cages model reduced the maximum von Mises stress on the implants by >90% in extension, flexion, lateral bending and axial rotation.

Interpretation: The finite element model study indicated that, compared with posterior C1-C2 pedicle screws fixation, atlantoaxial intraarticular fusion cages with posterior pedicle screws fixation could not only significantly restore stability to the atlantoaxial junction, but also dramatically reduce the maximum von Mises stress in the C1-C2 pedicle screws.