A comparison of rigid, semi-rigid and flexible spinal stabilization devices: A finite element study

Pedicle-screw-based spinal fixation system has shown its success for treating degenerative disc disease-related back pain and spinal instability. In the last few decades, several non-fusion implants ( 'flexible' or 'dynamic' fixation) are developed for treating slight degenerate disc disease. The aim of this study is to characterize and compare the biomechanical responses of pedicle-screw-based fusion with various rod materials and a flexible spinal stabilization device on the lumbar spine (L3L5). Computed tomography scan-based finite element model and pedicle screw fixation with rigid rod material stainless steel rod, semi-rigid rod material poly-ether-ether-ketone and flexible rod device made of stainless steel are used in this study. Intact model of the lumbar spine and treated with all the different implants are simulated under typical physiological loading conditions. Compared with the intact model, pedicle screw with the stainless steel rod fixation system is found to offer very less range of motion. Poly-ether-ether-ketone rod system increased range of motion 3.8, 7 and 1.8 times for axial rotation, lateral bending and flexion-extension, respectively, compared to the stainless steel rod system. The flexible rod device rod system is found to reduce stress on vertebral body, carrying out more loads as compared to poly-ether-ether-ketone rods. In the case of stainless steel rods, range of motion is almost restricted on the fusion zone, which is overcome by the poly-ether-ether-ketone rod system to some extent and farther improved by the flexible rod device rod system. So, the poly-ether-ether-ketone rod and flexible rod device rod systems may be implemented for better clinical results after succeeding experimental validation and clinical trial.