Biomechanical Research On The Cage Subsidence Influenced By The Matching Between Cage Morphology And Endplate

Objective:The cage subsidence begins with the collapse of the cage-bone interface and is one of the common complications after lumbar interbody fusion.With the rapid development of medical technology,it is possible to design implants that are more closely matched to the patient's anatomy.This study aimed of investigating the effect of lumbar fusion cage morphology and endplate matching on the strength of the cage-bone interface,and provide an experimental basis for whether the patient-specific interbody cage can reduce the risk of cage subsidence.Methods:1.twelve lumbar vertebrae specimens of 6 months old were selected.The image data of computerized tomography(CT)was analysised by picture archiving and communication system.The anatomical parameters included:Endplate width upper(EPWu),Endplate depth upper(EPDu),lower endplate width lower(EPWI),lower endplate depth lower(EPDI).Combining the relevant anatomical parameters of human lumbar endplates reported in the literature,design and make a fusion cage mold that can be used in this experiment,2.Using the high-strength and self-coagulation properties of the polymethylmethacrylate to make a cage matching perfectly with the endplate surface,and then use the matched cage and the mismatched cage for biomechanical study.Eight specimens were used for endplate axial compression experiments,four specimens were used for endplate cyclic compression experiments.The specimens were divided into four groups:the upper endplate mismatched group;the upper endplate matched group;the lower endplate mismatched group;and the lower endplate matched group.The maximum compressive load of the endplate,the displacement under the maximum compressive load and stiffness,and the subsidence of the cage under different cycles were measured to compare the effects of two different cage shapes on the strength and stiffness of the endplate.Results:1.The results of porcine specimen measurement:the upper endplate width accounted for 63.3%-65.1%of the human lumbar spine,the upper endplate depth accounted for 43.2%-46.6%of the human lumbar spine,and the lower endplate width accounted for 63.7%-66.1%of the human lumbar spine,the lower endplate depth accounted for 41.6%-43.8%of the human lumbar spine,the porcine lumbar vertebra endplate was larger on transverse diameter than human and narrower on sagittal diameter.2.Endplate axial compression test:There is no significant difference of the maximum compression load between the mismatched group and the matching group(P>0.05).The displacement under the maximum compression load of the matched group is less than the unmatched group(P<0.05).The matched group stiffness value is higher than the mismatch group(P<0.05).There was no significant difference of the mechanical properties between the upper and lower endplates under different matching conditions(P>0.05).The matched cages significantly improved the stiffness of the upper endplate by 53.5%and the lower endplate by 47.2%.3.Endplate cyclic compression experiment:The subsidence distance of the matched group was smaller than that of the unmatched group under different cycles(P<0.05).The cage exhibited a faster sinking speed in the initial stages of the cycle experiment and subsequently showed a slower subsidence trend.Conclusion:The matching between the shape of the cage and the endplate have an important influence on the cage subsidence.Patient-specific cage matching with the endplate can improve the stiffness of the cage-bone interface and reduce the risk of cage subsidence.