Stress analysis of the screw of atlantoaxial posterior screw fixation C1LM-C2PS and C1LM-C2PARS with and without rod: A FEM based study

Abstract

Human cervical spine consists of three vertebrae C0-occiput, C1-atlas, & C3-axial in its upper part. The atlantoaxial complex is the most portable segment of the cervical spine and is accountable for half of the flexion, extension, and axial rotation movements of the neck. Atlantoaxial cervical spine injuries are serious injuries since there is a likely risk of harm to the spinal cord. Sustaining stability of the atlantoaxial joint following a neck injury is a difficult task because both vertebrae have complicated anatomy. Thus, the strength of a bone screw is especially significant in the early post-operative stages. Different stabilization procedures have been accounted for C1-C2 injury fixation, out of which fixation with transarticular screws is considered as the gold standard procedure. But screw malposition and high riding transverse foramen of the C2 vertebra are some limitations of this fixation technique. Current FE-based study provides a comparison of the biomechanical stability of the two different atlantoaxial posterior screw fixation techniques (C1Lateral Mass-C2 Pedicle screws, C1Lateral Mass-C2PARS screws).In this work, a C1-C2 cervical spine model of a male patient is developed using MRI CT scan data using a 3-d slicer software and biomechanical stability comparison is done for C1LM-C2PS & C1LM-C2PARS screws fixed once with a supporting posterior screw fixation rod and once without rod under the physiological loading conditions of flexion, extension, lateral bending, and axial rotation using ANSYS WORKBENCH 16.2. The effects of the engaging supporting rod on the cervical spine were evaluated in the form of von-mises stresses induced in screws. Result shows reduction in screw stress values when implanted with supporting rods. C1LM-C2PS screw fixation with rod might be thought of as the best fixation solution for fractured C1-C2 vertebrae as it showed minimum stress values in the analysis as compared to C1LM-C2PARS with and without rod.