| Research backgroundLumbar degenerative diseases often require surgical treatment,which include posteriordecompression, pedicle screw fixation,disc removal and intervertebral bone graftfusion.Previous biomechanical researches and evaluation of spinal internal fixation deviceswere to simulate a spinal fracture and dislocation fixed with the fixation devices,then givethem the anteflexion, extension, left side bending,right side bending, compressive, torsiveloading or torque, to evaluate the stability by the displacement or the torsion Angle. There isno research of stress shield by simulation of posterior intervertebral fusion with threeintervertebral fusion devices in lumbar4、5degeneration with posterior pedicle screwfixationObjectiveTo simulate posterior intervertebral fusion with three intervertebral fusion devices withposterior pedicle screw fixation of lumbar4、5degeneration,then measure stress shield,cancellous bone density of the fixed vertebral part, do the bone histomorphometry and bonemorphological observation on the basis of strain electrical measuring technology andprinciple, the rheological characteristics theory and with the help of electron microscopy andimage analysis technology and etc. Give an objective and system evaluation to the syncreticeffect of three kinds of intervertebral fusion devices;to provide biomechanical basis for thechoice of reasonable operation, the appropriate fixation devices of lumbar degenerationand new type of fixed equipment design and development.Methods3.1group the specimensThe thirty porcine spine specimens with T12to S1were randomly divided into threegroups, posterior intervertebral fusion with bone graft group (bone graft group), posteriorintervertebral fusion with bone cage group (bone cage group), posterior intervertebral fusion with titanium mesh group (titanium mesh group),in simulation of lumbar4、5degenerationwith posterior pedicle screw fixation,each group have10specimens.3.2strain electrical measuring method of stress shield effect in each groupFirst measure the strain of each group before internal fixation. To simulate thebiological function of human,give the specimens compressive, anteflexion, extension, leftside bending, right side bending loading, do the strain electrical measurement of every pointof three groups after pastering of electric resistance strain gage by the help of the electronicaluniversal testing machine, calculate stress of every point by the one-way Hook’s Law. Thenmeasure the strain of each group after internal fixation.Remove the electric resistance straingage, give the specimens24hours to recover,simulate the model off posterior intervertebralfusion with three intervertebral fusion devices in lumbar4、5degeneration with posteriorpedicle screw fixation,do the same work as before.3.3bone density measuring methodAfter strain electrical measurement of each specimen, measure the bone density byXR-600Dual-energy X-ray bone density instrument produced in America. The cancellousbone is carried from the same fringe of each fixed position of each group.3.4method of histological observation of the boneAfter strain electrical measurement of each specimen, carry cancellous bone from thesame fringe of each fixed position of each group,then fixed, dehydration, non-decalcification,do the section of8μm thickness，then do histological observation of the section by scanningelectron microscope produced by Zeiss company in Germany3.5measuring method of the cancellous bone histomorphologyAfter strain electrical measurement of each specimen, carry cancellous bone from thesame fringe of each fixed position of each group,then fixed, decalcification,enbedding,do thesection of5μm thickness，measure the trabecular bone surface perimeter, trabecular bonesurface acreage, bone mass (trabecular bone), the trabecular bone thickness, degree ofseparation of the trabecular bone with the help of the image analysis systemResults4.1The strain electrical measuring results show that the strain and the stress of the bonegraft group is bigger than the bone cage group and the titanium mesh group under thecompressive, anteflexion, extension, left side bending, right side bending loading at everymeasuring point, which has significant difference (P <0.05),the strain and the stress of thebone cage group is bigger than the titanium mesh group under the compressive, anteflexion, extension, left side bending, right side bending loading at every measuring point, whichhas significant difference (P <0.05).4.2The measuring results of the bone density show that the bone density of the controllgroup is bigger than the titanium mesh group,the bone cage group and the bone graft group,which has significant difference (P <0.05), the bone density of the titanium mesh group isbigger than the bone cage group and the bone graft group, which has significant difference(P <0.05), the bone density of the bone cage group is bigger than the bone graft group,which has significant difference (P <0.05).4.3The histological observation of the cancellous bone show that the trabecula of thecontroll group is fine and dense,the structure is in alignment, some of the trabecula of thetitanium mesh group is thinner and the structure have a certain degree disorder, most of thetrabecula of the bone cage group is thinner and the structure is in a mess, almost all of thetrabecula of the bone graft group is thinner and the structure is in a chaos,there is gap in it.4.4The measuring results of the cancellous bone histomorphology show that thetrabecular bone surface perimeter, trabecular bone surface acreage, bone mass (trabecularbone), the trabecular bone thickness, degree of separation of the trabecular bone of thecontroll group pairs respectively with the titanium group, the bone cage group,the bone graftgroup, the matching t-test has statistical significance (P <0.05). The measuring results of thecancellous bone histomorphology show that the trabecular bone surface perimeter, trabecularbone surface acreage, bone mass (trabecular bone), the trabecular bone thickness, degree ofseparation of the trabecular bone of the titanium mesh group pairs respectively with the bonecage group,the bone graft group, the matching t-test has statistical significance (P <0.05).The measuring results of the cancellous bone histomorphology show that the trabecular bonesurface perimeter, trabecular bone surface acreage, bone mass (trabecular bone), thetrabecular bone thickness, degree of separation of the trabecular bone of the bone cage grouppairs with the bone graft group, the matching t-test has statistical significance (P <0.05).Conclusions5.1The strain electrical measuring results show that the strain and the stress of thetitanium mesh group is smaller than the bone cage group and the titanium mesh group underthe compressive, anteflexion, extension, left side bending, right side bending loading atevery measuring point, which has significant difference (P <0.05), which illustrate that thestress shield of the titanium mesh group is the lowest. The strain and the stress of the bonecage group is smaller than the bone graft group under the compressive, anteflexion, extension, left side bending, right side bending loading at every measuring point, whichhas significant difference (P <0.05), which illustrate that the stress shield of the bone cagegroup is lower than the bone graft group. The titanium mesh group,the bone cage group andthe bone graft group has different stress shield.5.2The measuring results of the bone density show that the bone density of the titaniummesh group is bigger than the bone cage group and the bone graft group, which hasstatistical difference (P <0.05), which illustrate the cancellous bone’s injury of the titaniumis smallest under the loading.5.3The measuring results of the cancellous bone histomorphology show that thetrabecular bone surface perimeter, trabecular bone surface acreage, bone mass (trabecularbone), the trabecular bone thickness, degree of separation of the trabecular bone of thecontroll group pairs respectively with the titanium group, the bone cage group,the bone graftgroup, the matching t-test has statistical significance (P <0.05), which illustrate thecancellous bone’s injury of the titanium is smallest under different loading.5.4The histological observation of the cancellous bone show that the change of thetrabecula structure in the titanium mesh group is gentle.5.5The measuring results of the bone density show that the bone density was inverselyassociated with the stress shield effect, the greater of the bone density, the lower of the stressshield effect5.6The measuring results of the cancellous bone histomorphology show that thetrabecular bone surface perimeter, trabecular bone surface acreage, bone mass (trabecularbone), the trabecular bone thickness and stress shield are positive correlation, degree ofseparation of the trabecular bone and stress shield are negative correlation.5.7Posterior intervertebral fusion with titanium mesh in lumbar4、5degeneration withposterior pedicle screw fixation has a small stress concentration and stress shield effect. |
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