The Dynamic Changes In Lumbar Intervertebral Space Height During Motion And The Design Of Lumbar Facet Arthroplasty System

BackgroundWith the increasing social problems of degenerative lumbar diseases,an increasing number of research studies have focused on the biomechanical properties of the lumbar spine and treatments.Decompression and fusion fixation is regarded as the most widely used operation way in treating of spinal stenosis and degenerative disc diseases.But,fusion surgery would accelerate the degeneration of lumbar adjacent segments according to the results of long-term follow-up observation.In view of these clinical problems,some scholars have proposed the method of nonfusion technology in spine surgery.The purpose of this procedure is to preserve the motion of patient's lumbar spine and reduce the incidence of adjacent segment disease.Total lumbar facet arthroplasty system is a important way of this kind of spine surgery.But,this technology has not been used widely because of some reasons,for example,the size is not suitable for Chinese people,inadequacy of the structure and so on.So we will design a kind of total facet arthroplasty system according normal lumbar anatomic parameters.Method1.We firstly validated the accuracy and repeatability of a custom-made mechanical loading equipment.2.The changes of the disc height and the distance between the adjacent two pedicle screw entry points(DASEP)of the posterior approach at different lumbar levels(L3/4,L4/5,and L5/S1),were detected on three-dimensional lumbar models,which were reconstructed from the CT images of the different positions.3.We design a facet joint prosthesis using CAD(computer aided design)method.The FEA(finite element analysis)method was used to analyze the biomechanics of the prosthesis.4.We investigated the biomechanical property of the total facet arthroplasty system in vitro.Result1.We construct a custom-made mechanical loading equipment and it had a high accuracy and repeatability in determing of the segmental vertebrae position of the lumbar spine.2.The change in anterior disc height gradually increased from the upper to the lower levels(L3/4:1.56±0.30mm,L4/5:2.06±0.62mm,L5/S1:2.50±0.93mm),from neutral to flexion;the change in anterior disc height was significantly greater than the change in posterior disc height at L3/4 and L5/S1 from neutral to extension;however,the changes of disc lateral height were different from the changes of DASEP.3.We successfully established normal L2-L5 finite element model.The ROM(range of motion)of the nonfusion method was bigger than fusion group;and the max stress of facet joint prosthesis was lower than screw-rod.4.Stiffness of the nonfusion group was lower than fusion group and it was closer to intact group.Conclusion1.The changes in the intervertebral space height at different levels and positions have different characteristics during flexion-extension and bending motion.2.The new total facet arthroplasty system has a better biomechanical property according the results of finite element analysis.3.New prosthesis can provide a better biomechanical stability for lumbar spine in terms of lumbar stiffness.