The Clinical Outcome And Finite Element Analysis Of Pedicle Screw Augmentation Treated Degenerative Lumber Diseases With Osteoporosis

ObjectivesObserve the clinical outcome and finite element analysis of pedicle screw augmentation treated degenerative lumber diseases with osteoporosis.Methods58 patients followed up at least 2 years,were enrolled in our institute were retrospectively reviewed from Jan 2011 to Dec 2015,diagnosed as lumbar spondylolisthesis,or lumbar stenosis,with T score <-2.5SD of BMD,and received less three-segment PLIF/TLIF with pedicle screw.fixation system.They came from the first affiliated hospital of Guangzhou University of Chinese medicine,and they were divided into 2 groups,30(2 males,28 females)in Polymethylmethacrylate-augmented pedicle screw(PMMA-PS)group,the other 28(3 males,25 females)in conventional pedicle screw group(CPS).Surgical data including the operation time,intra-operative blood loss,hospitalization day and surgical complications were recorded,as well as the radiological parameters measured from the postoperative X-rays and CT scans containing the rates of unfusion,screw loosening and cage subsidence incidence.In addition,the visual analogue scores(VAS)and Oswestry disability index(ODI)were evaluated preoperatively and postoperatively.56 patients suffered from degenerative lumber diseases with osteoporosis,was treated by pedicle screw augmentation lumber interbody fusion.They came from the first affiliated hospital of Guangzhou University of Chinese medicine.They were divided into kidney yang deficiency group and yin deficiency group according to TCM syndrome type.In the last follow-up CT,the intervertebral fusion rate and pedicle screw loosening rate were compared between the two groups.4 finite element(FE)analysis models of L4-5 single segment and L3-5 two segments with augmentation or without augmentation intervertebral fusion models were established respectively.The stress of intervertebral discs,facet joints of the adjacent segments and the vertebral endplate after anterior flexion,left flexion and left rotation were analyzed respectively.ResultsThe average follow-up period was 34.32 months(ranging from 24 months to 51 months).Compared with PMMA-PS group,operation time and average hospital stay in the TPS group decreased significantly(P <0.05).While no statistical d i f f e r e n c e f o r b l o o d l o s s b e t w e e n 2 g r o u p s(P > 0.0 5).A t 2 y e a r s postoperative,from CT-scans,2/178 screws loosening and 1/59 segment non-union occurred in PMMA-PS group,with significant lower incidence than those in TPS group(8/152 screws loosening and 6/50 segments non-union occurred,P<0.05).Regarding to the cage subsidence,24 segments found height loss(5.30±1.92mm)in PMMA-PS group without difference compared with that of 19 segments(4.78±1.37mm)in CPS group(P >0.05).Besides,the number and location of the cages and the leakage of the cement were found out little related with the subsidence in the PMMA-PS group(P >0.05).After surgeries,VAS and ODI at 1month,6 months,12 months and last follow-up improved significantly in two groups(P <0.05).There were no significant differences of VAS and ODI preoperatively and postoperatively between 2 groups(P >0.05).In addition,8 patients asymptomatic trajectory PMMA leakages were detected.There were 32 patients in the kidney yang deficiency group,which included 53 fusion segments,and 37 patients in kidney yin deficiency group including 70 segments.In the last follow-up CT,8 non-fusion segments of the kidney yang deficiency group were found to be more than 2 segments of the kidney yin deficiency group,and the difference was statistically significant(P<0.05).In anterior flexion,single segment pedicle screw augmentation model could increase the pressure on the upper and lower endplates coming from cage and decrease the stress of the adjacent facet joint.As for two segment model,the pressure of fifth lumber upper endplate was increased.In left flexion,the pressure of fifth lumber upper endplate of single segment or two segment models with pedicle screw augmentation were both than other two models respectively.In left rotation,the pressure of fifth lumber upper endplate of single segment pedicle screw augmentation bigger than the anther.ConclusionCement-augmented pedicle screw technique is effective and safe in osteoporotic spine with lumbar degenerative diseases,with better fusion rates and less screw loosening incidence.There are no difference in the fusion rate and loosening rate between the two groups in the single segment patients,however,there are better fusion rate and lower pedicle screw loosening rate of the PSA group in the double or multiple groups patients.Cement-augmented pedicle screw does not bring about cage subsidence,which does not relate to the position and the sum of the cage.The fusion rate of patients with kidney yang deficiency is higher than that patients with kidney yin deficiency.However,more cases need further observation.Polymethylmethacrylate-augmented pedicle screw does not significantly increase the incidence of adjacent segment disease but it may lead to an increase in the stress of the intervertebral cage to the vertebral endplate,which may contribute to interbody fusion,but also increases the risk of intervertebral cage subsidence.