Biomechanical Performance Analyses And Topology Optimization Of An Interspinous Dynamic Stabilizer By Finite Element Method

Lumbar spinal stenosis results in a reduction in the effective volume in the patient's spinal canal,so that the neuro located in the spinal canal is oppressed.Patients may develop many symptoms including lower limb pain,low back pain,and intermittent claudication.Lumbar spinal stenosis influences the life quality of patients seriously.The most common treatment for lumbar spinal stenosis is decompression surgery and the use of internal fixation systems to improve the stability of the surgical segment.According to long-term clinical follow-up,the pedicle screw system can reduce the range of motion and improve the stability at the surgical segment,but it has a positive effect on the degeneration of adjacent segments and increases the risk of undergoing reoperation.In order to avoid emerging complications,interspinous process devices have gained in popularity for treating lumbar spinal stenosis,such as Wallis,X-STOP,DIAM and Coflex.Many experts and scholars analyzed their biomechanical properties by using finite element method,but few of them investigated biomechanical performances and optimized structure of the interspinous process device named StenoFix.Therefore,the main contents of this study include:First of all,a three-dimensional finite element model of intact lumbar was constructed and validated based on CT images.The concrete step was establishing the lumbar geometry model by using CT images and medical modeling software Mimics.The finite element pre-processing software ANSA was used to divide the finite element grid and check the quality.The corresponding material properties were assigned to the different parts in the finite element analyses software ABAQUS.According to the relevant experiments in vitro and simulation experiments,the correct boundary conditions and loads were applied to the model and the results were in good agreement with other people's researches.It demonstrated that established finite element model of lumbar spine in this study was available for further analyses.Then,a postoperative finite element model was established and biomechanical properties were analyzed.The interspinous ligament,the ligamentum flavum,and the local lamina between the L3 and L4 vertebrae were removed.The appropriate size of the interspinous process device was selected according to the distance between the L3-L4 spinous processes.After assembly,the appropriate boundary conditions and loads were applied to the postoperative model.The results demonstrated that interspinous process device provided stability at the surgical segment in all directions and didn't accelerate the degeneration of adjacent segments.When lumbar spine was in vibration environment,the maximum value and the vibration amplitude of intervertebral disc stress decreased at the surgical segment.Finally,the topology optimization design of the interspinous process device was carried out.The overall stiffness of the model was the optimization target,and the volume of the implantation was the constraint condition.According to the pseudo-density contour,the structure was redesigned and analyzed.The results indicated that the performance of improving the stability of the structure after optimization decreased slightly at the surgical segment when compared with structure before optimization.When lumbar spine was in vibration environment,the maximum value and the vibration amplitudes of intervertebral disc stress decreased significantly.