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

BACKGROUND: 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. OBJECTIVE: This study employs finite-element-analysis (FEA) to investigate the influence of PSF on the cervical spine under various loading conditions. METHODS: 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). RESULTS: 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. CONCLUSION: This present FE study provides the biomechanical efficacy of cervical PSF and its impact on spinal stability for restoring cervical spine biomechanics.