A Three-dimensional Finite Element Analysis Of The Biomechanical Properties Of A New Lumbar Spondylolysis Repair Device

Objective Through three-dimensional finite element analysis,the biomechanical properties of a new repair device for lumbar spondylolysis were analyzed,which provided a new choice for the treatment of lumbar spondylolysis.Methods The lumbosacral CT images of a healthy volunteer were collected,and the nonlinear L3-S1 finite element model(M0)was established and verified.On this basis,the L5 spondylolysis model(M1),the pedicle screw U-shaped rod fixation model(M2)and the new lumbar spondylolysis repair device fixation model(M3)were established respectively.The degrees of freedom of the lower surface of S1 vertebral body of the four models were constrained,and an axial compression force of 500 N and a moment load of 10N·m were applied to the upper surface of L3 vertebral body respectively to simulate six motion states of lumbar flexion,extension,left-right lateral bending and left-right rotation.The range of motion(ROM)of lumbar spine,the root stress of L5 spinous process and the axial pressure of isthmus of each finite element model in different motion states were compared.Results Compared with previous research results,the ROM of M0 model in L4-L5 and L5-S1 segments are similar to previous research results,which proves that this model is effective.Compared with the M1 model,the ROM of the surgically fixed model decreased significantly in all motion states,and the ROM of the M2 model and the M3 model decreased by 16.46%-55.98% and 17.48%-48.63% respectively.Compared with M2 model,the maximum stress of L5 spinous process decreased by 12.71%,54.95%,58.46%,53.97%,46.91% and 72.34% when M3 model flexion,extension,left and right lateral bending and left and right rotation,which effectively reduced the risk of spinous process fracture.The maximum stress of both M2 model and M3 model occurred in the rotating state.Compared with M2 model,the axial pressure of M3 model lumbar isthmus increased by 236.51%,282.51%,216.99%,231.47%,294.03% and 138.91% respectively,which can promote fracture healing more efficiently.The maximum axial pressure of M2 and M3 occurred models in the right rotation state,which were 5.14 N and 12.28 N respectively.Conclusions 1.In this study,a three-dimensional finite element model of L3-S1 of normal people was established and proved to be effective,which can be used for further research and analysis.2.The angular displacement of lumbar spondylolysis model is larger than that of normal lumbosacral model,and its stability is obviously reduced,which will lead to lumbar instability;3.The stability of the two surgical methods to fix lumbar spondylolysis is similar,which is beneficial to restore the biomechanical stability of lumbar spine and the fusion of isthmus bone graft,and reduce the complications caused by lumbar instability;4.The new lumbar spondylolysis repair device can make the vertebral body have lower stress at the spinous process and greater axial pressure at the isthmus,which can be used as an alternative treatment for U-shaped nail and rod internal fixation device.