| Objective: To investigate the biomechanical effect of the removal of internal fixation construct on adjacent segments of the lumbar spine after TLIF.Methods: 1.The CT data of a normal young people without lumbar diseases were collected,and the L3-S1 model of normal lumbar spine was extracted,smoothed,and assembled by Mimics,Geomagic,and Solidworks software.2.On the basis of normal model,TLIF operation was simulated,and the transpedicular fixator and Cage were implanted into L4-5 segment and L5-S1 segment to assemble L4-5 and L5-S1 TLIF model(fixation model).On the basis of TLIF surgical model,the transpedicular fixator was removed to assemble L4-5 segment and L5-S1 TLIF model without fixation construct models(fusion model).3.The materials and loading and boundary conditions were assigned to the models by ANSYS.The material assignment of bone was modified to obtain the fixation model of L4-5 segment and L5-S1 segment and the fusion model of L4-5 segment and L5-S1 segment in osteoporosis.4.Pre-load and moments were applied to the normal model,and pre-load and moments to reach the mobility of the normal lumbar model were applied to the fixation and fusion models.5.According to the different surgical segments,the models were divided into L4-5 surgical group(A group)and L5-S1 surgical group(B group),and the range of motion,the peak disc stress,the peak facet joint load,and the peak endplate stress of adjacent segments in each model were extracted as the results.The range of motion,the peak disc stress,and the peak endplate stress of adjacent segments of the two groups were analyzed by one-way repeated measures ANOVA.By comparing with the corresponding indexes of intact lumbar model,the range of motion,peak disc stress,peak facet joint load,and peak endplate stress of adjacent segments of each model were normalized to the percentage of the corresponding indexes of intact lumbar model,and the difference between the normalized percentage and the percentage of intact lumbar model was taken as the percentage result.Results: 1.L4-5 normal bone mass group: pairwise results showed that after the internal fixation construct was removed,compared with the fixation model,there were significant differences in the range of motion,disc peak stress of L3-4 and L5-S1 segments,and endplate peak stress of L3-4 segment(P<0.05),except that there was no significant difference in the endplate stress peak of L5-S1 segments in the fusion model(P>0.05).The percentage results showed that after the internal fixation construct was removed,compared with the fixation model,the range of motion,the disc peak stress,the endplates peak stress and the facet joint load of L3-4 and L5-S1 segments in the fusion model showed a downward trend.2.L4-5 osteoporosis group: The pairwise results showed that after the internal fixation construct was removed,compared with the fusion fixation model,there were significant differences in the range of motion,disc peak stress of L3-4 and L5-S1 and endplate peak stress of L3-4(P<0.05),except that there was no significant difference in the endplate peak stress of L5-S1 in the fusion model(P>0.05).The percentage results showed that after the internal fixation construct was removed,compared with the fixation model,the range of motion,the disc peak stress,the endplate peak stress and the facet joint load of L3-4 and L5-S1 segments in the fusion model showed a downward trend.However,the change trend is irregular,and the stress in some parts rises abnormally.3.L5-S1 normal bone mass group: The pairwise results showed that after the internal fixation construct was removed,compared with the fixation model,the range of motion,the disc peak stress and the endplate peak stress of L3-4 and L4-5 segments in the fusion model were statistically different(P<0.05).The percentage results showed that after the internal fixation was removed,compared with the fixation model,the range of motion,the disc peak stress,the endplate peak stress and the facet joint load of L3-4 and L4-5 segments in the fusion model showed a downward trend.4.L5-S1 osteoporosis group: The pairwise results showed that after the internal fixation construct was removed,compared with the fixation model,the range of motion,the disc peak stress and the endplate peak stress of L3-4 and L4-5 segments in the fusion model were statistically different,except that there was no significant difference in the peak stress of the upper endplate of L3-4 segment(P>0.05).The percentage results showed that after the internal fixation construct was removed,compared with the fixation model,the range of motion,the disc peak stress,the endplate peak stress and the facet joint load of L3-4 and L4-5 segments in the fusion model showed a downward trend.However,the change trend is irregular,and the stress in some parts rises abnormally.Conclusion: 1.Removal of internal fixation construct of normal bone patient can reduce the range of motion,the disc peak stress,facet joint load and endplate peak stress of fusion segments(L4-5 and L5-S1)of adjacent segments.Removal of internal fixation construct after TLIF in patients with normal bone is beneficial to reduce the incidence of complications such as ASD and promote the functional recovery of patients.2.Removal of the internal fixation construct in osteoporosis models can also reduce the range of motion,disc peak stress,facet joint load and endplate peak stress of fusion segments(L4-5 and L5-S1),but the range of motion,the disc peak stress,facet joint load and endplate peak stress in some parts will increase irregularly,which may increase the risk of degeneration.It is not recommended to remove the internal fixation construct unless necessary. |
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