Topology Optimization Design And Finite Element Analysis Of Artificial Lamina In Posterior Lumbar Laminectomy

Background:Posterior lumbar laminectomy and decompression is a common surgical method in spine surgery,but postoperative disruption of the posterior spinal ligamentous complex may lead to a series of postoperative complications.An individualized artificial lamina as a bionic implant can be well matched to the posterior vertebral surface after surgery to restore the posterior spinal structure.As an ideal metal implant material for orthopedics,titanium alloy has significant advantages in terms of mechanical properties as well as biocompatibility.However,existing artificial titanium alloy lamina are solid structures,heavy in mass and difficult to avoid stress shielding phenomenon,with poor bone and soft tissue growth into them.The topology optimization technique can optimize the material distribution in a given area by setting certain load and constraint conditions,and combined with the gradient layered microporous design of the artificial titanium alloy lamina,it can reduce the elastic modulus of the implant,reduce the stress shielding and reduce the mass.Finite element analysis techniques can simulate and analyze the real human force situation and optimize the design of the prosthesis in collaboration with topology optimization techniques.Therefore,the aim of this study is to design an individualized artificial titanium alloy lamina to reconstruct the posterior spinal structure after laminectomy,and to investigate the biomechanical effects of the artificial lamina by topology optimization design with finite element analysis technique,so as to provide a new idea for the design of artificial titanium alloy lamina.Methods:Based on the CT data of a healthy adult to construct a model of the intact lumbar spine,simulate the procedure of lumbar laminectomy alone to establish a laminectomy surgical model.At the same time,by modifying the resected lamina,a bionic artificial lamina was designed,and the designed artificial lamina was implanted to construct the artificial lamina implantation surgical model.The three models were subjected to finite element analysis to measure and compare the range of motion of the surgical segment and adjacent segments,the intradiscal pressure and the peak stress of the annulus fibrosus under different motion conditions of the different surgical models.Based on the finite element analysis,topological optimization of the target region of the artificial lamina was performed with volume as the constraint and minimum strain energy as the objective function,and the stress distribution of the artificial lamina was compared before and after optimization.Results:The lumbar decompression surgery model showed increased range of motion,intradiscal pressure,and peak fibrous annulus stress in the operated segment and adjacent segments under all conditions compared with the intact model.Compared with the intact model,the artificial lamina implantation surgical model increased in flexion only by 7.5%-22.5%,7.6%-17.9%,and 6.4%-19.3%,respectively.The highest peak stresses for the fixation screw and the artificial lamina were 46.53 MPa and 53.84 MPa during axial rotation,respectively.The stresses in the artificial lamina were mainly concentrated at the spinous root,the area surrounding the screw hole,as well as the contact area with the vertebral body.The optimized artificial lamina was reduced in mass and its peak stresses were 31.3 MPa and 50.91 MPa under lateral bending and axial rotation conditions,respectively,which were 2.6 MPa and 2.93 MPa less than before optimization.Conclusions:The individualized bionic artificial lamina can achieve perfect matching,better maintain the biomechanical properties of the intact lumbar spine,maintain the original mobility of the lumbar spine,reduce the intradiscal pressure and annulus fibrosus stress in the adjacent segments,and reduce the occurrence of diseases in the adjacent segments.Topology optimization can further improve the biomechanical properties of the artificial lamina,reduce stress shielding,facilitate the growth of bone and soft tissues into it,and achieve lightweight design,which provides a new idea for the design of artificial lamina.