Clinical And Finite Element Study Of The Effect Of Segmental Lumbar Lordosis Changes On Adjacent Segment Degeneration

Objective: The study aimed to explore the effect of segmental lumbar lordosis changes on adjacent segment degeneration by the finite element method and retrospective study.Methods: Totally 77 patients who underwent posterior lumbar interbody fusion(PLIF)of L4-L5 in our hospital from January 2018 to September 2020 and met the selection criteria were included in our study.41 patients in group A(≥ 5 °)and 36 patients in group B(<5 °)were divided according to whether the changes of segmental lumbar lordosis after PLIF was greater than 5 °.The following contents were recorded: gender,age,BMI,follow-up time,operation time,intraoperative blood loss,hospital stays;clinical scores before the operation and in the last follow-up including Oswestry disability index(ODI)and visual analogue scale(VAS).Adjacent segment degeneration(ASD)in the two groups was diagnosed according to preoperative and follow-up X-ray changes.Using t-test and chi-square test to compare the statistical differences between the two groups and using logistic regression to analyze the independent risk factors affecting the occurrence of ASD after the operation.Using Mimics,Solid Works,and Geomagic wrap software to build two groups of models.Then using Ansys software to carry out finite element analysis on them,and compare the range of motion(ROM)of adjacent segments and the Von Mises stress of intervertebral disc between the two groups of finite element models.Results: There was no significant difference in age,gender,BMI,follow-up time,operation time,intraoperative blood loss and hospital stays between the two groups(P>0.05).Clinical efficacy results: Before the operation,there were no significant differences in VAS and ODI between the two groups(P>0.05).At the last follow-up,the VAS and ODI of patients in both groups were significantly lower than those Before the operation(P<0.05),and the VAS and ODI of patients in group A were significantly lower than those of patients in group B(P<0.05).Adjacent segment degeneration results:At the last follow-up,there were 5 cases(12.2%)of ASD in Group A and 13 cases(36.1%)of ASD in Group B.The rate of adjacent segment degeneration in Group A was significantly lower than that in group B(P<0.05).Among the 5 cases in group A,4 cases(9.8%)had degeneration of the head-end and 1 case(2.4%)had degeneration of the tailend,there was no significant difference between the proportion of head-end degeneration and tail-end degeneration in Group A(P>0.05).Among the 13cases within group B,10(27.8%)had degeneration of the head-end and 3(8.3%)had degeneration of the tail-end.The proportion of head-end degeneration in Group B was significantly higher than that of tail-end degeneration(P<0.05).The patients were divided into the ASD group and No-ASD group according to whether ASD occurred after the operation.Logistic regression analysis of the factors influencing the occurrence of adjacent segment degeneration after surgery revealed that age and the changes in segmental lumbar lordosis were independent risk factors for ASD after posterior lumbar interbody fusion(P<0.05).The results of finite element analysis:The range of motion of adjacent segments in group B was generally higher than that of group A under different motion states such as flexion,extension,bending,and rotation;Except for the extension of the L5-S1 segments,the von Mises stress on the intervertebral disc of the adjacent segment in group B was greater than that in group A.Conclusion:1.In posterior lumbar interbody fusion,increasing the segmental lumbar lordosis is more beneficial to the improvement of the patient’s functional status.2.Age and segmental lumbar lordosis changes are independent risk factors for the development of ASD after posterior lumbar fusion,and the incidence of adjacent segmental degeneration increases significantly with poor recovery of the segmental lumbar lordosis,with a greater risk of headend adjacent segmental degeneration.3.For patients undergoing posterior lumbar interbody fusion,the biomechanical changes caused by poor recovery of the segmental lumbar lordosis changes increase the risk of adjacent segment degeneration.