Biomechanical Analysis Comparison of Different Cervical Posterior Screw Fixation Techniques: A Finite Element Study

To biomechanically compare the stress distribution of established posterior cervical fixation techniques-conventional pedicle screw (PS), Abumi technique, unicortical lateral mass screw (LMS), and bicortical LMS-with a novel PS method, the Lee point technique, using finite element modeling (FEM).

A patient-specific FEM of C5-6 was developed using high-resolution computed tomography scan data of a degenerative cervical spine. Five fixation models were constructed: Lee point, Abumi, conventional PS, unicortical LMS, and bicortical LMS. Screw dimensions were ø3.5×28 mm for PS and ø3.5×14/18 mm for LMS. A pure moment of 1.0 N·m was applied in flexion, extension, axial rotation, and lateral bending, and the peak von Mises stress (PVMS) of both the vertebrae and implants was recorded for each loading condition.

Abumi technique showed the highest PVMS at C5-6 (23.09-43.22 MPa and 24.96-39.91 MPa), with stress concentrated at the pedicle entry and medial wall. Lee point and conventional PS demonstrated more evenly distributed stress across the pedicle and near cortex of the lateral mass. Unicortical and bicortical LMS showed stress mainly at the entry point, with overall lower and more uniform magnitudes. Implant stress was greatest in Abumi construct (up to 295 MPa), moderate in Lee and conventional PS, and lowest in LMS models.

Abumi technique showed higher localized stress concentrations that may warrant careful patient selection, particularly in those with compromised bone quality. Lee point technique achieved a balanced stress profile comparable to conventional PS, suggesting a favorable biomechanical profile for posterior cervical fixation.