The Biomechanics And Clinical Study On Effects Of L_3/4 Intervertebral Space After L_4/5 Artificial Disc Replacement

Functional spinal unit (FSU) is the Complex includingintervertebral disc, ligament, articular process, articular capsule andadjacent vertebral body. It is the fundamental unit of spine motion.Intervertebral disc is the load and motion center of the FSU.Degenerationdisease of intervertebral disc is the primary cause of lower back pain.Traditionary operation includes discectomy or discectomy withfusion.But discectomy always decrease the height of intervertebral spaceand the stability of lumbar vertebrae segment; discectomy with fusionwill result in Adjacent Segment Disease(ASD).The purpose of Artificialdisc replacement (ADR) is just to re-establish the physiologic function ofintervertebral disc.Because intervertebral disc is the load and motion center of theFSU,it is valuabal to study the mechanism of degeneration disease ofintervertebral disc.Up to now ADR is not used widely, there was fewreports about its effect to lumbar, and no corresponding reports abouteffects to adjacent disc compared among discectomy, discectomy withfusion and ADR.Wafer-shaped stress sensor was used to measure the intervertebraldisc pressure during the biomechartical test in this study. In order toreveal the correlation between the operation methods(discectomy, ADR,or intervertebral fusion)and adjacent superior intervertebral space.Theintervertebral space pressure of the L_3/4 were measured which appliedwith load of neutrality and flexion, extension, lateral bending. Thenconclude the effect on the adjacent superior disc after the differenttreatment. Furthermore the clinical cases of the discetomy, artificial discreplacement and intervertebral fusion were followed in 6, 12, 24, 36 months. The clinical result of the different treatment were evaluated, andthe relationship of the different treatment to the degeneration ofsuperior intervertebral disc were also evaluated by X ray.PART ONE: Measuremennt to intervertebral space pressureObjective: To explore the stress change in L_3/4 intervertebral spaceby biomechanical study.Methods: To explore the stress change in L_3/4 intervertebral spaceunder axial, flexion, extension, lateral bending loads by wafer-shapedstress sensor designed ourseves. All data was statistical analyzed withSPSS 11.0 for windows. Comparisons with values of P＜0.05 wereconsidered statistically significant.Results: the stress change were different in L_3/4 intervertebralspace under different kinds of loading. The pressure is higher with flexionthan with axial load and lateral bending which is higher than withextension(P＜0.05).Conclusions: The stress change were different in L_3/4intervertebral space under different kinds of loading. Our wafer-shapedstress sensor was efficient for testing intervertebral spac pressure. PART TWO: The biomechanical research of the stresschange in superior intervertebral space after artificial discreplacementObjectives To compare the stress change of the L_3/4 intervertebralspace after L_4/5 discetomy, artificial disc replacement, and theintervertebral fusion during with the different motion condition, and toobserve the biomechanical effect on the superior intervertebral spaceMethods 10 fresh lumbar spinal specimens(L1～S2) obtained fromyoung adult cadavers, during the biomechanical measurement, specimenswere divided into integrity group, discectomy group, artificial discreplacement group and intervertebral fusion group of L_4/5. Theload(2000N) of neutrality and pure moments (10Nm) of axial, flexion,extension, lateral bending were applied on each group. The stress changeof the L_3/4 intervertebral space were measured with wafer-shaped stresssensor. Paired-samples T Test was used to detect significant changes ofthe difference in stress between the four groups after loading (α=0.05).Results (1)Under all kinds of loading, the disectomy indicated adecrease of the stress in the L_3/4 intervertebral space compared to intactcondition, but P＜0.05 until loading was higher than a centainpoint,otherwise p＞0.05. (2)The interbody fusion resulted in significantincrease of the stress in L_3/4 intervertebral space compared to intactcondition(under axial, flexion and lateral bending loading,P＜0.001; underextension loading,P＜0.05). (3)Under all kinds of loading,the ADRindicate no difference of the stress in L_3/4 intervertebral space comparedto intact condition(P＞0.05).Conclusions A new human cadaver lumbar interbody fusionmodel was invented. The stress of L_3/4 after L_4/5 ADR was not changed which indicated it can maintain normal biomechanical function; Thestress decreasd after discectomy which indicated it can influence thestress distribution of adjacent segment; the fusion will increase stress inadjacent intervertebral space significantly indicated that the fusion is mostlikely to result in the stress concentration of adjacent segment.PART THREE: A clinical study of the change of thesuperior intervertebral space after artificial discreplacementObjectives To evaluate the therapeutic results among artificial discreplacement, discectomy and fusion;to fred out the relationship betweenoperation methods and the degree of degeneration on the adjacentsuperior intervertebral space in order to provide reference for operativemethod choosing and clinic prognosis.Methods 20 patients underwent uni-segment ADR, 20 patientsunderwent uni-segment disc excision, and 20 patients underwentuni-segment fusion from 1999 to 2004 with complete data were involved.All cases were followed-up more than 3 years, their clinical symptomsand signs were evaluated by the Japanese Orthopaedic Association scores(JOA) and VAS at 6 months, 12 months, 24 months and 36monthsfollow-up.The pykno of end plate calcification, intervertebral spacestenosis, osteophyma, intervertebral space Wedge shaped in L_3/4intervertebral space were recorded by X ray. All data recorded werecompared with statistical methodsResults: 1. JOA scores were much higher at any follow-up in allthree different surgical operations than those at pre-operation (P＜0.01). 2. Group ADR and fusion had higher JOA scores than those in groupfenestration with statistical difference at 24 months follow-up, but thedifference between fusion and ADR group was no significance instatistics at that time. 3. Group ADR and fusion had higher JOA scoresthan those in group fenestration with statistical difference at 36 monthsfollow-up; the difference between fusion and ADR group was alsosignificanct in statistics. 4. JOA scores in ADR group was no difference instatistics at 36 months follow-up when comparison to those at 6 months,but decreased with time in fenestration and fusion group, which had astatistical sense. 5.Compaired the abnormal signs in L_3/4 intervertebralspace among the 3 groups:there was no different at 6 and 12 months;at 24and 36 months fusion group was much more than ADR and fenestrationgroup,p＜0.01,at the same time fenestration group was more than ADRgroup,p＜0.05.Conclusions All three surgical interventions had therapeutic butdifferent effects for LDH; the therapeutic effect of ADR is best and moststable among the three methods.The study shows that the interbodyfusion will result in the degeneration or acceleration of the degenerationin L_3/4 intervertebral space; ADR can avoid degeneration of adjacentlevel; discectomy also can result in the degeneration of adjacent superiorleve,but the degree is lower then fusion.