Change of mobility and stress morphology due to different types of artificial cervical spine implementation: A finite element analysis

The purpose of this study was to analyze the mobility and stress morphology of different implants, in order to provide a clinical reference for individual needs. Three types of commercial cervical implants namely Bryan Disc, Prodics-C, and Prestige were reconstructed according to the product information. A displacement controlled non-linear FEM was analyzed and compared. All models were subjected to a sequential rotation in flexion-extension, lateral bending, and axial torsion using the LS-DYNA prescribed motion analysis. The range of segmental motion (ROM), facet joint force, tension on major ligaments, and stresses on the cores were analyzed. Unlike the spinal fusion, the stress level and the mobility in adjacent levels didn't increase significantly for all types of disc arthroplasties but ROM at C5 level did increase particularly in the fixed core design of Prodisc-C. The metal-on-metal design (Prestige) limited the ROM which resulted in stiffening the spinal column structure. The instantaneous center of rotation moved to near facet joints after cervical arthroplasties. The multi-articulation design of the Bryan Disc would induce overall better biomechanical benefits for the cervical spinal disc replacement than other designs. Different design characteristics result in different kinematics and kinetics. A multi-articular metal-on-polymer mobile core provides better functions than other implants.