The Effect of PEEK-Rod Fixation Systems on Finite Element Lumbar Spine Model

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Orthopedic fixation devices have been employed in the treatment of spinal diseases. Special fixation devices have been developed to decrease the effect of spinal injuries and deformities and have been used to decrease the neurologic back pain of the patients. In this study, the finite element spine model of an adolescent idiopathic scoliotic patient was constructed. The titanium spinal implant system and the system of polyetheretherketone (PEEK) were compared regarding their stress distributions. The finite element lumbar spine model from L2 to L5 vertebra was obtained from computed tomography scan data. The three-dimensional spine model consisted of four lumbar vertebrae, three intervertebral discs, six facet joints, and the corresponding ligaments. Loading and boundary conditions were applied to the L2-L5 lumbar model. According to the subjected loads and bending moments on the model, stress distributions were evaluated especially on the intervertebral discs, and the screw-rod implant systems both for the titanium and the PEEK-based fixation systems. The disc structures were also analyzed for the effects of adjacent segment disease, which has been reported as a post-operative effect of fusion surgeries. Ansys software was used for the simulation processes of the models without the implant system and the models with different fixation systems. Comparative investigation between different fixation systems showed that the stress distribution values were decreased with the PEEK-based fixation system. Moreover, lower total deformation and equivalent stress values were recorded with the PEEK-based fixation system, especially on L3-L4 and L4-L5 intervertebral discs. Furthermore, both spinal implant systems allowed to decrease the overall loading stress on the whole spine models. And it was concluded that the PEEK-based spinal implant system was considerably reduced the load on the discs and ligaments, and also appeared as a better option in stress reduction and load sharing when compared to the titanium spinal implant system.