Finite element analysis of biomechanical performance of atlanto-axial bony structure following artificial atlanto-odontoid joint arthroplasty

Abstract

Objective To investigate the stress characteristics of atlanto-axial bony structure under conditions of anteflexion,posterior extension,lateral flexion,and rotation after artificial atlanto-odontoid joint arthroplasty using three-dimensional finite element method and to improve the orientation of artificial atlantoodontoid joint from perspective of stress.Methods A three-dimensional finite element model of prosthetic atlanto-odontoid joint arthroplasty was created from CT images of the artificial atlantoodontoid joint and cervical vertebrae using software Mimics,Freeform,and Ansys.Stress characteristics of the model dealt with proneness,posterior extension,lateral flexion,or rotation loads were observed.Biomechanical performance of the bony structure of the model was analyzed and the orientation in improving the prosthesis was discussed.Results Anteflexion loading produced a maximum stress of 0.138 ×l08 N/m2 at the junction of lateral mass and posterior arch of the atlas,and 0.201 × 108 N/m2 at axial nail hole,contact point of plates with the axis,and posterior arch of the axis.Posterior extension loading produced a maximum stress of 0.666 × 107 N/m2 at junction of lateral mass and posterior arch of the atlas and 0.254 × 108 N/m2 at arch of the axis.Besides,stress concentration occurred at atlantoaxis nail hole.Right bending produced a maximum stress of 0.124 × 108 N/m2 at nail hole of right mass of atlas and 0.178 × 108 N/m2 at right contact point of the axis with plates.Right rotation produced a maximum stress of 0.847 × 107 N/m2 at junction of lateral mass and posterior arch of the atlas and 0.170 × 109 N/m2 at contact point of the axis with plates.The finite element model comprised 28 620 nodes and 107 441 units and provided good defining of the structural properties of artificial atlanto-odontoid joint arthroplasty.Under different loading conditions,the stress was mainly distributed in contact point of the vertebral body with plates,nail holes,junction of lateral mass and posterior arch of the atlas,and axial pedicle.Conclusions Prosthetic atlanto-odontoid joint scatters a part of the stress and alters the stress distribution of the atlas and axis from the intact condition.Finite element method can obtain complete analysis of the stress distribution of the artificial atlanto-odontoid joint arthroplasty. Key words: Cervical vertebrae; Biomechanics; Finite element method ; Atlanto-odontoid joint