The Biomechanical Study And Clinical Observation On The Effects Of Two Level Cervical Artificial Disc Replacement On Adjacent Superior Segment Zygapophyseal Joint

Cervical spondylosis is a common degenerative spinal disease.Anterior cervical decompression and fusion is a effective mean forthe management of cervical spondylosis. But the incidence ofadjacent level intervertebal disc pathology secondary to anteriorcervical fusion, by changing the stress on zygapophyseal joints andthe motional mechanics between levels, has been well reported inclinical and laboratory studies. Artificial cervical discreplacements(ACDR) is a new technique developing in the recentyears to provide a new approach for the treatment of cervicalspondylosis. The purpose of ACDR is to replace degenerative discand exertion its function, and to preserve normal physiologicaloperative level motion and decrease the incidence of adjacent levelpathology secondary to anterior cervical fusion. ACDR at one levelhad a many of biomechanical studies and clinical reports. Butcervical spondylosis commonly involved in two or more level,whether two level ACDR measures up to normal cervicalbiomechanics is needed to further clinical and laboratory research.The zygapophyseal joints have a very great significance. Theybear different type of loadings such as compression, traction,shearing and torsion. The adjacent level degeneration is closelyrelated to its biomechanical property and it is one of the mostimportant values used in evaluating the outcomes of cervical surgicalinterventions. Therefore, biomechanical research on zygapophysealjoints has great clinical significance. The clinical and laboratoryresearch related with the influence of two level ACDR on superiorzygapophyseal joint had no reported at present.Cervical degeneration commonly involved in C_4/5 and C_5/6 twolevel owing to cervical physiological characteristic. The currentstudy was undertaken to investigate the influence of two level CADR on adjacent superior zygapophyseal joint from the followingbiomechanical and clinical aspects: (1)To investigate the influencearising from ACD, ACDF and ACDR at C_4/5 and C_5/6 two level freshcadaveric cervical specimens under various loadings on C_4/5 and C_3/4zygapophyseal joint pressures;(2)To observe the clinical early stageoutcomes of ACDR and clinical outcomes of ACDF at C_4/5 and C_5/6two level, and to investigate their influence on the degeneration ofadjacent superior zygapophyseal joint.CHAPTER ONE: The Laboratory Investigation of the Influencesof Two Level Cervical Artificial Disc Replacement on Adjacentsuperior Zygapophyseal Joint PressureObjectives: To investigate the influence caused by C_4/5 and C_5/6two level ACD, ACDR and ACDF on the pressures at C_4/5zygapophyseal joint and adjacent superior zygapophyseal joint C_3/4, thusto provide references for clinical application of two level ACDR.Methods: A total of 11 fresh and intact human cadaveric cervicalspines (C₃-T₁) were used in this investigation. According to thesequence of the experiment, all specimens were sequentiallyreconstructed at C_4/5 and C_5/6 with four model groups as 1) total discintact, 2) C_4/5 and C_5/6 discectomy, 3) C_4/5 and C_5/6 ACDR, and 4) C_4-6ACDF. Testing was performed in displacement control under axialrotation, lateral bending, flexion and extension loading modes onspecimens. A miniature wafer-like pressure transducers we designed byourselves was inserted to monitor adjacent superior zygapophyseal jointpressures and C_4/5 zygapophyseal joint under various grades of loading indifferent groups. Various pressures collected from different groups werecompared by statistic analysis through SPSS11.5 for windows solfware.Results: After the implementation of ACDR, ACD and ACDF at C_4/5 and C_5/6 by performing in displacement control under axialrotation, lateral bending, flexion and extension loading modes, the overalltrend of change at C_3/4 and C_4/5 zygapophyseal joint pressures is:â‘ Thepressures in different groups were higher as the grades of the loadingwere higher. The pressures of ACDF at C_4/5 zygapophyseal joint was zero.â‘¡The pressures at C_3/4 and C_4/5 zygapophyseal joint of the ACDR groupcompared with the total disc intact group had no statistical significance(P＞0.05).â‘¢The pressures in C_3/4 and C_4/5 zygapophyseal joint of theACD group compared with the total disc intact group and the ACDRgroup were lower in small loadings(under 100N) and higher in largeloadings(beyond 100N). The pressure values of the ACD group comparedwith the total disc intact group and the ACDR group had statisticalsignificance (P＜0.05).â‘£The pressures at C_3/4 zygapophyseal joint ofACDF group were higher. The pressure values compared with the othershad statistical significance (P＜0.05)Conclusions: 1. The pressure values of C_4/5 zygapophyseal jointand adjacent superior level zygapophyseal joint C_3/4 at two levelACDR compared with the total disc intact group had no statisticalsignificance. Consequently, it suggests that two level ACDRmeasures up to normal cervical biological mechanics. 2. Thepressure values of C_4/5 zygapophyseal joint and adjacent superiorlevel zygapophyseal joint C_3/4 in two level ACD decreased in smallloadings, but the pressures were higher as the grades of the loadingwere larger. It suggests this has changed the distribution of stresswithin cervical spines and it is likely to be one of the reasons lead todegeneration of adjacent superior segment. 3. The increase of adjacentsuperior zygapophyseal joint pressure caused by ACDF is likely to be oneof the reasons that cause or accelerate the degeneration of adjacent superiorsegment. CHAPTER TWO: Clinical Observation of the Influences of Twolevel Cervical Artificial Disc Replacement on adjacentsuperior zygapophyseal joints at the Early Stage.Objectives: To observe the early stage outcomes of ACDR andthe clinical outcomes of ACDF at C_4/5 and C_5/6 two level and toinvestigate their Influences on the degeneration of adjacentsuperior zygapophysealjoints.Methods: 35 patients who underwent surgical interventions for thetreatment of cervical spondylosis were collected and grouped in threeaccording to the respective ways of surgery they underwent andthe length of following-up study: (1) 5 patients in ACDR groupwith a follow-up study of 12～22 months(average 14.66 months); (2) 15patients in ACDF short term group (ACDF group one) with a follow-upstudy of 1～2.5 years(average 15.75 months); (3) 15 patients in ACDFmedium and long term group (ACDF group two) with afollow-up study of 5～8 years(average 6.75 years). The JapaneseOrthopedics Association Back scores (JOA), the Odom grades and thefull range of motion shown by X ray of adjacent superior segments in bothpre-opemtion and post-operation, i.e., 6 months, 1 year, 2 years and 5 yearsthereafter were analyzed, and the degrees of degeneration revealed by CTscans on adjacent superior zygapophyseal joints at post-operative stage, i.e.,6 months, 1 year, 2 years and 5 years thereafter were analyzed as well.SPSS11.5 for windows software was used to undertake a comparativeanalysis among various groups at various stages.Results: 1. The post-operative JOA scores and Odom grades haveobviously increased in three groups (P＜0.01). 2. For 6 months afteroperation, the different JOA scores, Odom grades, the ranges of motionof adjacent superior segments and degeneration of adjacent superiorzygapophyseal joints in ACDR group and ACDF group one have no statistic significance (P＞0.05). 3. For 6- month and 12-monthpost-operative follow-up, the different JOA scores, Odom grades anddegeneration of adjacent superior zygapophyseal joints in ACDF groupone and ACDF group two had no statistic difference (P＞0.05);But theranges of motion of adjacent superior segments in two groups haveincreased(P＜0.05). 4. the JOA scores and Odom grades of 5 yearpost-operative compared with 1-year post-operative follow-up and 2-yearpost-operative follow-up in ACDF group two had statisticalsignificance(P＜0.05). The ranges of motion of adjacent superiorsegments had increased(P＜0.05). Degeneration of adjacent superiorzygapophyseal joints finds the increased (P＜0.05).Conclusions: 1. Two level ACDR is one of effective therapeuticmeans in many segments cervical spondylosis. The clinical therapeuticeffect of the early stage of postoperation is satisfactory. The ranges ofmotion of adjacent superior segments were good. adjacent superiorzygapophyseal joints had no obvious degeneration. 2. Two level ACDF isalso one of effective therapeutic means in many segments cervicalspondylosis. Degeneration of adjacent superior zygapophyseal joints at theearly stage of postoperation are not obvious. Degeneration of adjacentsuperior zygapophyseal joints at the medium and long stage ofpostoperation is likely to be relation with accumulated stress. 2. Themedium and long term Clinical effect of ACDF decreases anddegeneration occurs in adjacent superior zygapophyseal joints. 3. Wehave no enough clinical cases with two level ACDR and the time ofapplication of it is shorter, so a further observation related to medium andlong term Clinical effect of ACDR is necessary. Appendix:Superior and inferior zygapophyseal and medical isthmus make upof the cervical lateral masses. Superior and inferior zygapophysealbetween adjacent segments form the zygapophyseal joint. The bilateralzygapophyseal joints and cervical disc contribute jointly the stability tocervical spine. Cervical lateral mass is the foundation of the technique oflateral mass screw fixation. The purpose of current study is to evaluatethe safety of the technique of the screw fixation of cervical lateral massby observing and measuring the relation between cervical lateralmasses(C₃～C₇) and their adjacent anatomical structures, thus to provideanatomical reference for clinical application of the technique;The Applied Anatomy and the Radiological Measurementsof the Cervical Lateral Mass and their Clinical significanceObjectives: To evaluate the safety of the technique of the screwfixation of cervical lateral mass by observing and measuring therelation between cervical lateral masses(C₃-C₇) and their adjacentanatomical structures, thus to provide anatomical reference forclinical application of the technique.Methods:â‘ A total of 21 adult's human cadaveric cervicalspine(Including 11 fresh-frozen cervical spine and 10 preservativecadavers, and C₃～T₁ segment spine)were used in this study toobserve and measure the distances(D₁ and D₂)between C₃～C₇cervical lateral masses and their adjacent cervical nerveroots(including superior nerve roots and inferior nerve roots );â‘¡Atotal of 40 adult's lateral cervical radiographs were selected tomeasure the inclination angles of the uparticular facet of lateralmasses(αangle);â‘¢A total of 20 CT scanning with mid-line ofadult's cervical lateral mass were used in the study. We defined thelmm point internal of the midpoint of lateral masses as O point and measure the angles(βangles) between the line from O point to theoutskirts of the transverse foramen and sagittal plane; the distancebetween O point and front-outside of lateral masses; and theangles(θangles) between the line from O point to the front-outsideof lateral masses and sagittal plane.Results:â‘ The cervical nerve roots are traversing from thefront-outsides of the lateral masses. In the up-outside quadrant therearen't nerve roots. The distances(D₁) from the midpoint of front-outsides of lateral masses to the superior nerve roots are small, rangefrom 2.38～2.77mm; The distances(D₂) from the midpoint of thefront-outside of lateral masses to the inferior nerve roots are far from6.72～7.06mm;â‘¡The inclination angles of uparticular facet oflateral(αangle) in C₃～C₇ are range from 50.9～59.10°, C₃＞C₄＞C₅＜C₆＜C₇, it is the smallest in C₅ and it is the largest in C₇.â‘¢Theoutcomes of CT scanning measurement of the cervical lateral masses:the angles(βangle) between the line from O point to the outsides ofthe transverse foramen and sagittal plane incline to inside in C₃～C₅,average value is respectiveiy 3.0°,3.2°,2.7°. It incline to outside inC₆, average value is 7.1°; The distances from O point to thefront-outside of lateral masses are range from 11.8～13.5mm; Theangles(θangle) between the line from O point to the front-outsideof the lateral masses and sagittal plane are rang from33.4-34.1°.Conclusions:â‘ According to the anatomical observation andmeasurement of cervical lateral masses, the distance between lateralmass and superior nerve root is small. It suggests the degenerationsof uparticular easily affects the superior nerve root.â‘¡According tothe results from the observation of anatomy and the measurement ofradiographs, the screw penetration of cervical lateral massesmaintain ahead-incline 35～45°and outside-incline 10～30°, thevertebral artery and nerve roots don't be injured.â‘¢For thedifference of the lateral mass in different person, practising the difference of the screw penetration in the screw fixation of lateralmasses according to different person is necessary for the largestgrisping of the screw.