Effect of pedicle-screw fixation on cervical spine: A comparative finite element analysis

Pedicle-screw-fixation (PSF) is a widely used surgical technique for stabilizing the cervical spine in cases of trauma, degenerative diseases and deformities. However, the biomechanical effects of PSF on cervical spine stability remain a topic of research.

This study employs finite-element-analysis (FEA) to investigate the influence of PSF on the cervical spine under various loading conditions.

A three-dimensional (3D) finite element model of the cervical spine (C2-C7) is developed, validated and subjected to simulated flexion, extension, lateral bending and axial rotation. Four scenarios are compared: (1) Intact spine (C2-C7), (2) spine with PSF at fourth segment (C4-C5), (3) spine with PSF at fifth segment (C5-C6) and (4) spine with two level PSF at fourth and fifth segments (C4-C6).

The results demonstrate that due to single segment PSF, the total ROM (second to sixth segments) is reduced by 8.8%, 8.5%, 12.4% and 11.4% whereas two segment PSF shows that the total ROM is reduced by 24.2%, 23.3%, 23.5% and 25.3% under 1 N-m flexion, extension, lateral bending and rotations, respectively, in comparison to intact cervical spine. The maximum stresses on Titanium alloy (Ti-6Al-4V) Pedicle-screw are varied from 70 to 75 MPa and on PEEK rod are around 32-40 MPa, respectively. The maximum stresses on pedicle-screw and rod material are also below its yield stress.

This present FE study provides the biomechanical efficacy of cervical PSF and its impact on spinal stability for restoring cervical spine biomechanics.