| Objective:To provide data for the development of an expandable elastic lumbar intervertebral fusion device that meets the anatomical characteristics of the Chinese population,has a reasonable design,is easy to operate,and has strong interface stability and high self-stabilization performance.Its biomechanical properties in TLIF surgery were investigated by three-dimensional finite element analysis.Methods:1.The imaging data related to the design of the fusion device were obtained by measuring the CT and MRI of the lumbar spine in our outpatients and inpatients to provide a theoretical basis for the design.2.On the basis of establishing the finite element model of L3-L5 vertebral body in normal human,the TLIF surgical procedure was simulated in L4/5 segment,and the new expanded intervertebral fusion and normal intervertebral fusion models were constructed respectively to analyze the Von-Mises stress and distribution of the two fusion devices,the Von-Mises stress of the posterior pedicle nail rod system,the Von-Mises stress of the adjacent intervertebral disc,the Von-Mises stress of the contralateral minor articular eminence,and range of motion(ROM)of the L4/5 segment in both models were analyzed.Results:1.New fusion width range: PLIF: L3/4 segment retained part of the inferior articular eminence 3.90 ± 1.81 ～ 8.12 ± 1.88mm;removal of the inferior articular eminence 10.43±1.34 mm.L4/5 segment retained part of the inferior articular eminence 5.38±2.15～10.59±2.16mm;removal of the inferior articular eminence 14.56 ± 1.92 mm.The L5/S1 segment retained part of the inferior articular eminence 7.24±2.63 to 12.33±2.53 mm;the inferior articular eminence 16.87±1.87 mm was removed.TLIF: L3/4 segmental preserved portion of superior articular eminence8.12±1.88～9.87±2.03mm;removal of superior articular eminence 16.51±2.16 mm.L4/5 segmental preserved portion of superior articular eminence10.59 ± 2.16 ～ 12.81 ± 2.56mm;removal of superior articular eminence19.26 ± 1.86 mm.L5/S1 segmental preserved portion of Superior articular eminence 12.33 ± 2.53 ～ 15.65 ± 2.87mm;removal of superior articular eminence 19.90±2.12 mm.There were significant differences in fusion height and angle across segments: the L3-S1 intervertebral gap anterior,mid,and posterior heights at the same measurement location were significantly different between segments using a one-way ANOVA SNK-q test for two-way comparisons(P<0.01).The maximum anterior height of L5/S1 was 11.91±1.57 mm,the maximum mid height of L4/5 was 11.81 ± 1.60 mm,and the minimum posterior height of L5/S1 was 6.82±1.19 mm in each gap.Vertebral gap formation angles of L3/4(5.09±1.42)°,L4/5(5.84±1.44)°,and L5/S1(8.27±2.11)° were significant difference between two comparisons using one-way ANOVA SNK-q test(P<0.05).2.The maximum stress values of the expansive fuser were 34.06,24.07,54.29,53.71,53.73,and 55.36 MPa under six different working conditions,and the maximum stress values of the normal fuser were 99.05,29.75,61.41,67.39,68.05,and 70.87 MPa,respectively,while the stress clouds can be visualized from The blue area of the expansive fuser is more and more uniform than that of the normal type fuser.Under six different working conditions,the vertebral activity of the expanded fusion group was 0.75,0.42,0.26,0.37,0.31 and 0.23,respectively,while the vertebral activity of the normal fusion group was 0.86,0.53,0.38,0.43,0.27 and 0.28,respectively,which can be seen from the experimental results that the vertebral activity of the expanded fusion is smaller than that of the normal fusion.The experimental results showed that the vertebral body mobility of the expanded fusion was less than that of the normal fusion.The peak stresses of the pedicle screw system in the expanded interbody fusion model were 66.70,64.88,102.80,53.60,90.91,86.49,and the peak stresses of the pedicle screw system in the normal interbody fusion model were 75.42,60.62,94.38,71.30,90.18,75.35,respectively.The peak stresses of the pedicle screw system in the expanded interbody fusion model were greater in posterior extension,left lateral bending,and right and left rotation than those in the normal interbody fusion model,and less in anterior flexion and right lateral bending.The peak disc stresses were 2.59,1.80,2.47,2.46,2.61,and 2.40 in the adjacent segment(L3/4)of the expanded intervertebral fusion model and 2.58,1.79,3.06,2.34,2.57,and 2.39 in the adjacent segment(L3/4)of the normal intervertebral fusion model,respectively,and the peak stresses in the expanded intervertebral fusion model were 2.58,1.79,3.06,2.34,2.57,and2.39 in left-sided bending.The peak stresses in the adjacent segments of the model were smaller than those of the normal intervertebral fusion,and the rest of the conditions were not much different from those of the normal intervertebral fusion.The peak stresses in the contralateral small joints of the expanded interbody fusion model were 2.21,4.96,5.19,3.59,3.01,and 2.52,respectively,and the peak stresses in the contralateral small joints of the normal interbody fusion model were 2.31,5.34,5.26,3.88,3.85,and 2.70,respectively,suggesting that the expanded interbody fusion would reduce the stress loads in the contralateral small joints.Conclusions:1.This experiment yielded a range of fusion widths and a range of heights and angles that varied significantly across the different vertebral spaces,across the different surgical approaches,and across the extent of preserved articular processes.In order to maintain the biomechanical stability of the lumbar spine as much as possible and to preserve some of the articular processes,the study used a fusion width of 12 mm or less in the PLIF surgical approach and a fusion width of 16 mm or less in the TLIF surgical approach,and a fusion width of 17 mm or less if all of the inferior articular processes were removed in the PLIF surgery and 20 mm or less if all of the articular processes were removed in the TLIF surgery.The initial height of the fusion should be in the range of 6-9mm and the initial angle of the fusion should be 4-7°.As the anterior height > mid-height > posterior height of L5/S1,the angle of the intervertebral space is larger than the other gaps,and for the specificity of the height and angle of its,the larger anterior height and angle can be maintained by means of reverse expansion of the expansile fusion.2.In this study,the three-dimensional finite element model of two different fusion devices implanted with bilateral pedicle screw fixation under the TLIF procedure,and the comparative analysis of the computational results showed that the new expanded fusion device can significantly disperse the endplate stress load,while making the vertebral body mobility significantly reduced and limiting the vertebral body movement,which can effectively avoid the fusion device sinking while promoting the fusion between the vertebral bodies,and also reduce the contralateral small joint synapse It can also reduce the stress load on the contralateral small joint synapse and slow down the degeneration.Although the peak stress of the pedicle screw system of the expanded intervertebral fusion is larger than that of the pedicle screw system of the ordinary intervertebral fusion model during posterior extension,left lateral bending and left-right rotation,the peak stress of the nail rod is much smaller than its yield strength under different motion conditions,which can effectively avoid the occurrence of fatigue fracture in the long term.The peak stress in the adjacent segment of the expanded intervertebral fusion model during left lateral bending was smaller than that of the common intervertebral fusion,and the difference between the two was not significant in the rest of the working conditions.The expanded fusion can effectively prevent the occurrence of ASD by reducing the disc stress in the adjacent segment. |
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