Design And Research Of Customized Lumbar Artificial Lamina Under Additive Manufacturing And Its Biomechanical And Biological Verification

Posterior laminectomy is widely used in daily clinical work.It is an effective way of spinal canal decompression.Laminectomy is mainly used for spinal canal decompression in spinal malfunctions including intraspinal tumors,spinal canal stenosis,ossification of ligamentum flavum,and serious fractures.However,postoperative complications such as iatrogenic spinal instability and epidural fibrosis will cause the recurrence of neurological symptoms.At the same time,spinal segments are not easy to identify after laminectomy,which increases the difficulty of secondary surgery.Therefore,intraoperative navigation is often needed to avoid spinal cord injury.Considering the advantages and disadvantages of posterior lumbar laminectomy,scholars seek to develop and design a prosthesis that can replace autologous lamina,namely artificial lamina.Artificial lamina is synthetic lamina tissue composed of various materials and forms.It aims to improve the stability after laminectomy by reconstructing the posterior structure of the spine.Individual differences in the population limit the application of mass production of artificial lamina.Therefore,there is an urgent need to solve this problem.Additive manufacturing(AM)is a method based on computer-assistant to generate three-dimensional images,which can accurately manufacture a variety of physical structures.It has been applied in the fields of industrial design,architecture,engineering,automobile,and aerospace design.In medicine,AM can be applied to preoperative planning,surgical instrument designing,and customized design of implanted prostheses.Finite element analysis(FEA)is a method to simulate the real stress of the material by dividing the target material into finite elements and analyzing the stress of each element.FEA can be used to analyze the mechanical distribution of implant prosthesis and spine,as well as to explore the biomechanical characteristics of the implant.Therefore,we applied FEA and AM to the design and development of artificial lamina.Objective:To explore the theoretical and biological characteristics of artificial lamina by computer assistant technology,and to provide a theoretical basis for the research and application of artificial lamina in clinical biomechanics.The significance of this study is to design the artificial lamina prosthesis through additive manufacturing and finite element analysis technology,explore its biomechanical distribution,improve spinal stability,and reduce spinal degeneration.Meanwhile,artificial lamina can provide a physical barrier between the dura mater and posterior tissue,avoid epidural fibrosis,reconstruct posterior structure,regain spinal stability,and reduce the recurrence of neurological symptoms.After biomechanical and biological verification,the system can be used as the theoretical basis for clinically customized artificial lamina prostheses in the future,and improve the postoperative quality of life of patients undergoing lumbar surgery.Method:A lumbar heterogeneous nonlinear model was established based on volunteer lumbar CT data.A novel type of artificial lamina prosthesis was designed by computer-aided engineering.All parts of the lumbar elements and accessories’positions were adjusted and assembled to simulate the surgical process.A laminectomy model and a customized artificial lamina implantation model were established by the finite element technique.Under the conditions of load and boundary constraints,the stress and strain of the lumbar spine before and after laminectomy were compared to that of an intact model.The finite element analysis of the implant prosthesis was conducted to clarify the biomechanical properties of the artificial lamina.Secondly,additive manufacturing technology was applied to print the titanium alloy-made artificial lamina prosthesis,and the biomechanical experiment was completed using a mechanical experimental machine.The experimental results and the finite element analysis results were compared to verify the FEA accuracy,and comprehensively clarify the biomechanical mechanism of individualized lumbar artificial lamina according to the finite element analysis and biomechanical experimental results.Finally,the additive-manufactured artificial lamina prostheses were implanted into rabbits in animal experiments.Thirty New Zealand white male rabbits undergoing an L5/6 laminectomy were used to evaluate the effects of artificial laminae on antiepidural fibrosis properties.Finite element analysis(FEA)data were compared between different models.Pairs of samples were compared using a t-test,and groups were compared using one-way ANOVA.The level of significance was set at p-values less than 0.01 or 0.05.Results:The heterogeneous nonlinear finite element model of the lumbar spine established in this study can be used in subsequent mechanical analysis after confirming its convergence,sensitivity,and effectiveness verification.The finite element analysis of the laminectomy model showed that posterior laminectomy increased the lumbar range of motion and the intradiscal pressure in the adjacent segment of the spine.FEA showed that implantation of artificial lamina improved the stability of the lumbar column by reducing overall ROMs by 6.9%,8.5%,and 9.2-9.4%in flexion,extension,and axial rotation compared to the laminectomy model,respectively.Artificial lamina implantation was able to reduce the intradiscal pressure resulting from laminectomy by sharing the stress in the lumbar system,with 18.14%of L3-4 in flexion,4.22%of L4-5 in extension,and 6.77%of L1-2 in axial rotation.The stress distribution of artificial lamina and matching screws under different boundary conditions obtained by finite element analysis has shown that the implantation of lamina can share the mechanical load imposed on the lumbar system and verifies the biomechanical properties of the artificial lamina.Meanwhile,the crosssectional area(262.7±1.1 mm~2 vs 411.7±6.1 mm~2,p<0.01)and anteroposterior diameter(15.95±0.35 mm vs 23.58 ± 0.18 mm,p<0.01)of spinal canal increased significantly before and after artificial lamina implantation.In the biomechanical experiment,the range of motion of the gross lumbar specimens before and after lamina implantation under the same pure motion is similar to that of the finite element analysis,which verifies the accuracy and reliability of the finite element analysis results.In the biological experiment,compared with the experimental animals in the laminectomy group,the experimental animals in the artificial laminectomy group did not have spinal cord compression,and the anteroposterior diameter of the spinal canal increased significantly before and after the operation(p<0.001).Histological analysis confirmed the preventive effect of artificial laminae in terms of epidural fibrosis,scar density,and epidural adhesion(p<0.05).Conclusion:The novel designed customized artificial lamina under additive manufacturing and finite element analysis can biomechanically support the spine after laminectomy,and biologically prevent lumbar fibrosis as a mechanical barrier between the dura mater and posterior tissue at the same time.