Biomechanical Analysis And Clinical Study On Optimization Of Intervertebral Fusion Device In Lateral Lumbar Interbody Fusion Surgery

Part Qne Impact of Cage Position on Biomechanical Performance of Stand-Alone Lateral Lumbar Interbody Fusion: A Finite Element AnalysisObjective: This study aimed to compare the biomechanical performance of various cage positions in stand-alone lateral lumbar interbody fusion(SA LLIF).Methods: An intact finite element model of the L3-L5 was reconstructed.The model was verified and analyzed.Through changing the position of the cage,SA LLIF was established in four directions: anterior placement(AP),middle placement(MP),posterior placement(PP),oblique placement(OP).A 400 N vertical axial pre-load was imposed on the superior surface of L3 and a 10N/m moment was applied on the L3 superior surface along the radial direction to simulate movements of flexion,extension,lateral bending,and axial rotation.Various biomechanical parameters were evaluated for intact and implanted models in all loading conditions,including the range of motion(ROM)and maximum stress.Results: In the SA LLIF models,the ROM of L4-5 was reduced by84.21-89.03% in flexion,72.64-82.26% in extension,92.5-95.85% in right and left lateral bending,and 87.22-92.77% in right and left axial rotation,respectively.Meanwhile,ROM of L3-4 was mildly increased by an average of9.6% in all motion directions.Almost all stress peaks were increased after SA LLIF,including adjacent disc,facet joints,and endplates.MP had lower stress peaks of cage and endplates in most motion modes.In terms of the stress on facet joints and disc of the cephalad segment,MP had the smallest increment.Conclusion: In our study,SA LLIF risked accelerating the adjacent segment degeneration.The cage position had an influence on the distribution of endplate stress and the magnitude of facet joint stress.Compared with other positions,MP had the slightest effect on the stress in the adjacent facet joints.Meanwhile,MP seems to play an important role in reducing the risk of cage subsidence.Part Two Topology Optimization of Fusion Device in Lateral Lumbar Interbody Fusion Surgery based on Finite Element Nume-rical TechniqueObjective: To explore the topology optimization design of interbody fusion device in Lateral Lumbar Interbody Fusion(LLIF)surgery using finite element numerical technique,and evaluate its biomechanical characteristics.Methods: The complete L3-L5 spinal model,interbody fusion device,and pedicle screws were reconstructed using finite element analysis software(MIMICS,Geomagic,Solid Works).The L4/L5 intervertebral disc was removed and the interbody fusion device was inserted,followed by the assembly of the posterior pedicle screws.The model was imported into Ansys for static analysis,coupled with the topological optimization module for topology optimization.The static analysis conditions were as follows: the L3 upper surface was preloaded with a vertical axis load of 400 N,and a torque of10N·m was applied radially to simulate flexion-extension,lateral bending,and axial rotation.The topological optimization conditions were as follows: the maximum number of iterations was set to 500,the minimum normalized density was set to 1.e-003,the convergence accuracy was 0.1%,and the penalty factor was set to 3.The minimum member size region,AM hanging constraint region,and filter were set to exclude exceptional situations.The optimized model was then smoothed and re-analyzed for statics,and compared with the original model.Results: The experimental results achieved convergence after 36 iterations based on density.The volume of the optimized interbody fusion device model was reduced by 38% compared to the initial model.In terms of stress distribution frequency,the stress distribution of the optimized model was more uniform.The stress peaks of the optimized model were slightly higher than those of the original model in extension and right bending(4% and 2%respectively),but decreased in other motion conditions(3% in flexion,6% in left bending,5% in left rotation,and 4% in right rotation).In all motion conditions,the strain energy of the optimized model decreased(8.2% in flexion,8.6% in extension,14.8% in left bending,10.7% in right bending,14.1% in left rotation,and 12.4% in right rotation).Conclusion: The topologically optimized interbody fusion device can achieve the same level of support strength and load-carrying capacity as the original model,while improving stability and reducing stress shielding effects.In addition,the optimized model provides a larger bone graft window that is conducive to interbody fusion.Finite element-based topological optimization provides ideas for personalized applications of spinal implants and promotes the wider application of lateral lumbar interbody fusion surgery.Part Three Analysis of factors related to the selection of intervertebral cage height in lateral lumbar interbody fusionObjective: To investigate the correlation between patient-specific parameters and the height of intervertebral cages in LLIF.Methods: Retrospective analysis was performed on clinical data of 79 patients who underwent transforaminal lumbar interbody fusion surgery at the Third Hospital of Hebei Medical University from January 2019 to June 2022.Patients were routinely screened upon admission with lumbar spine anteroposterior and lateral X-rays in flexion,extension,and neutral positions for preoperative geometric parameter measurements.Patient information,including gender,age,height,range of motion at the surgical segment,and intervertebral height index(IHI)were recorded.Results: A total of 74 patients were included in the study,with an average age of 57.1 years.Of these,there were 32 male patients and 42 female patients.There was a statistically significant difference in cage height selection between different genders(P=0.024,α:Mann-Whitney test),with male patients having a greater cage height(11.7±1.1 cm)than female patients(10.9±1.5 mm).Among them,37 patients were taller than 164 cm(10.8±1.5mm),and 37 patients were shorter than 164 cm(11.6±1.1 mm),and there was a statistically significant difference between the two groups(P=0.012,φ:Student’s test).Among all patients,the highest incidence of disease occurred in the L4/5 segment(51 cases,11.9±0.7 mm),followed by L3/4(15 cases,10.0±0.1 mm)and L2/3(8 cases,8.7±1.4 mm),with statistically significant differences in data(P<0.001,δ: ANOVA test).The highest cage was used in the L4/5 segment.Correlation analysis was conducted between AGE,IHI,ROM and cage height,respectively.The results showed that the p value of age was significantly greater than 0.05,indicating that there was no significant correlation between age and cage height.Cage height was significantly correlated with IHI(P<0.001),with r=0.795,indicating a significant positive correlation between the two.The p value of ROM was close to 0.05,and the r value was relatively low,indicating that the correlation of ROM was not significant.Conclusions: In LLIF,the selection of Cage needs to take into account various factors,including the patient’s gender,height,and other influencing factors.Relatively speaking,a higher Cage is needed for the L4/5 segment,and preoperative measurement of the intervertebral height index of the surgical segment can provide a reference for selecting a suitable height of the Cage during the surgery.