Research And Application Of Anterior Pedicle Screw Fixation In Lower Cervical Spine

The lower cervical spine (C3-C7) diseases serious impact on humanhealth, to surgical treatment of lower cervical spine diseases, the purposecan be attributed to: restore the anatomy of the cervical spine sequence,nerve root or spinal cord decompression and reconstruction of cervicalstability. Cervical internal fixation is an effective means of achievingthese objectives, the surgical approach is divided into anterior surgery andposterior surgery, mainly to make the selection according to the patient’sdisease indications for surgery. Posterior internal fixation, includinginterspinous wiring、 lamina clips Luque rods or Luque ring fixed、cervical lateral mass screw fixation, Margel screws and cervical pediclescrews, et al. For thoracolumbar fixation methods in the large number ofexperiments have been confirmed that transpedicular screw internalfixation compared with other methods, its highest biomechanical stability,has been in clinical widely used short-term and long-term efficacysatisfaction. However, due to the small cervical pedicle, adjacent to the complex anatomical structure has not been the attempt of this internalfixation. Until the the1994, Abumi first reported clinical use of theposterior pedicle screw fixation in cervical spine trauma, degenerative,deformity and obtained succession, After that, more and more scholarshave researche the posterior cervical pedicle screw fixation on basic andclinical. The results show that the technique can achieve true spinalthree-column fixation and greatest screw pull out strength, at the sametime, the incidence of internal fixation loosening、failure、implantdisplacement and instability again significantly reduced, and so far hasbeen clinically accepted gradually become a routine surgical. But thestudy also found that the risk of the surgical screw placement may damagethe vertebral artery, spinal cord and nerve roots, causing seriouscomplications, therefore, the accuracy of pedicle screws placement iscrucial.Internal fixation for anterior cervical surgery currently the mainuse vertebral screws-and-plate fixation system. Many patients haverequired multilevel anterior decompression and reconstruction in clincial,In these case,the fusion and complication rates postoperative have beenshown a direct correlation with the mechanical stability of the fixation.That great spinal stability contribute to the higher fusion rate, the lowerrate of corresponding near-term and long-term postoperativecomplications. However, in case of severe three-column subaxial cervical spine fractures, multilevels vertebral discectomies or corpectomie,vertebral body tumor or infection, especially with serious osteoporosispatients, the traditional anterior cervical vertebral screw plate fixationsystem has been challenged, because vertebral mainly composed ofcancellous bone, with a thin cortex,n so the anchorage characteristics arelower, biomechanical stability is limited. In such cases,supplementalposterior stabilization is often needed. How can these patients only sufferanterior fixation to get the same efficacy as before and reduce thecomplication risk by secondary posterior fixation? So we investigated anew way of cervical internal fixation reconstruction technique:anteriorpedicle screw(APS) fixation. Our study from the cervical pediclemorphological observation of physical anatomy and imaging anatomycharacteristics, measure the the pedicle diameter line and angle, statisticalanalysis of these anatomical parameters, which, proved theoreticallyfeasibility of cervical APS fixation techniques..Then simulated surgicalscrew placement in vitro specimens, postoperative radiographic evaluation,so as to verify the safety and accuracy of the APS technology. Finally,under strict conditions to grasp the surgery indications used in clinicalpreliminary，further validate the practical operability of the lower cervicalspine APS fixation techniques and clinical effect, existence problems.Professional R&D at the same time supporting the surgical methodsscrew plate fixation system. The purpose is to provide theoretical and practical basis for large-scale promotion APS techniques in clinical. Theresearch mainly includes four parts:PART ONE:ANTERIOR PEDICLE SCREW INSERTION FOR LOWCERVICAL SPINE: ANATOMICAL OBSERVATIONObjective：To observe the pathlines and angles related to lowercervical spine anterior pedicle screw (APS) fixation in adults so as toprovide anatomical parameters in clinics.Methods: A total of22cervical spine (C3-C7) specimens of humanadult cadavers were individually measured by hand and CT scan todetermine the height and width of the narrowest part in pedicle, thicknessof inner and outer cortexes, pedicle axis length and included angle of axesfollowed by statistical methods. One hundred pieces of CT images from CTdatabase were randomly selected, then three-dimensional modelreconstruction was performed by Mimics software, relative parameters ofscrew insertion point were measured and95%confidence interval of screwinsertion parameters was also calculated.Results: No significant difference of pathlines and anglesmeasurements of22specimens was found between manual work group andCT scan group. Basing on the calculation of measurements of adult lowercervical spines in CT images with95%confidence interval, the insertionpoints for C3and C4was2-3mm opposite from operated pedicle incentrum median plane and6-7mm from upper end-plate of centrum plane, the outside inclined angle of screw insertion was46°-48°.Craniallyinclined angles for C3and C4were-11°--12°and-6°--7°respectively.The insertion point for C5was1-2mm beside operated pedicle in centrummedian plane and7-8mm from upper end-plate of centrum plane,theoutside and cranially inclined angles of screw insertion were47°-49°and1°-2°respectively. The insertion points for C6and C7were at the same sidewith operated pedicle,4-5mm beside centrum median plane and7.5-8.5mm from upper end-plate of centrum plane. The outside inclined angles ofscrew insertion for C6and C7were40°-42°and36°-38°respectively,cranially inclined angles were6°-7°and11°-13°. For insertion screws, thelength should be30mm,32mm or34mm and the diameter should be3.5mm or4.0mm.Conclusions: This study confirms the accuracy of CT scan in themeasurement of lower cervical spine and APS fixation related parametersand makes an exploration in technical range of parameters for the first timein the country using a large sample.PART TWO:EXPERIMENTAL STUDY ON LOWER CERVICALSPINE ANTERIOR PEDICLE SCREW INSERTIONObjective：To study the feasibility of lower cervical spine anteriorpedicle screw (APS) insertion and provide basis for its clinical application,according to the preoperative APS related technological parameters, onwhich strict performance was based. Methods：Normal cervical spine specimens of18cadavers werecarefully dissected to resect the surrounding tissue and clearly expose thecentrum antetheca. Following the CT scans, three dimensional model wasreconstructed by mimic software, the imaging data to measured keyparameters of anteroir transpedicular screw fixation by mimics software.The individual screw insertion parameters including intersection point（projective point of pedicle central axis on centrum antetheca）, insertionangle(the inclined angle of screws in cross-sectional and sagittal plane ofcentrum) and screws length of C3–C7were measured. Under direct vision,we strictly inserted pedicle screws according to the measurements resultsand evaluated efficacy by postoperative CT scans. Results The insertionpoints for C3and C4was2-3mm beside centrum median plane and in theopposite of operated pedicle,6-7mm from upper end-plate of centrumplane. The insertion points for C3-C7were in the same side of operatedpedicle, point for C5was1-2mm beside centrum median plane and7-7.5mm from upper end-plate of centrum plane. These parameters for C6andC7were4-5mm and7.5-8.5mm respectively. The screw insertiondirection was outside inclined in cross-sectional plane, and craniallyinclined in sagittal plane. The favorable outside inclined angles for C3orC4, C5and C6or C7were46°-47°,48°and36°-40respectively, craniallyinclined angles for them were-11°-7°,0°and8°-13°respectively. Thescrew length could be choosed among28mm,30mm and32mm, the screw diameter should be3.5mm. Basing on the relative measurements,we finally inserted144screws. Postoperative CT showed that all screwshave arrived lateral side via anterior insertion into pedicle inside, but therewere16screws exposure from pedicle lateral cortex, and3screwsperforating pedicle lateral cortex, which mostly occurred in C3and C4.Conclusion：Lower cervical spine anterior pedicle screw fixation isfeasible, the high accuracy and individuality of screw insertion are required.The APS could be applied for patients who need anterior approachoperation and strong fixation, it’s a alternative procedure.PART THREE:PRELIMINARY CLINICAL APPLICATION OFANTERIOR PEDICLE SCREW FIXATION OF LOWER CERVICALSPINEObjective：To discuss the feasibility and safety of anterior pediclescrew fixation in treatment of low cervical diseases.Methods： A total of10cases of low cervical diseases were treatedwith anterior pedicle screw (APS) fixation by us. All patients receivedpreoperative cervical CT scans, three-dimensional model reconstruction bymimics software and measurement of screw placementparameters(insertion point screw placement angle screw length anddiameter). All APS were performed through cervical anterior approach,then centrums antetheca and bilateral outer edges were exposed todistinguish and fix vertebral end plates, all were strictly operated under the fluoroscope assistance and preoperative measurements to insert screws.The postoperative efficacy of APS was evaluated by radiologist and otherorthopedist via anteroposterior and lateral radiation, CT scans, MRI, andthree-dimensional model reconstruction. A follow-up visit was did1,3,6and12months after operation.Results： Besides1screw for C4and1for C7,24screws for C3-C7were successfully inserted. Postoperative CT scans demonstrated4screwsbreaking outer vertebral wall. Besides1case suddenly dying from acutemyocardial infarction1week after operation, other9cases sufferedfollow-up visit. In3cases of trauma,1case did not get improvment butwith no aggravation according to Fankel grade. Other2cases achieved2ndand3rdgrade improvement with symptoms of nerve root irritationdisappearance or alleviation. Among6cases of non-trauma, spinal functionscore by JOA was averagely elevated to13.4scores, and the rate ofimprovement was60.7%according to Hirabayashi method. There was noserious complication except for2cases of dysphagia among all patients.Conclusion： Lower cervical spine anterior pedicle screw fixation isfeasible and relatively safe. The keys to success are preoperativemeasurement of individualized screw insertion parameters and appropriateapplication of intraoperative fluoroscope assistance. PART FOUR:PRELIMINARY DESIGN OF ANTERIOR PEDICLESCREW FIXATION SYSTEM IN LOWER CERVICAL SPINEObjective: a draft preliminary design of lower cervical pedicle screwplate systemMethods: based on the road of vertebral screw plate system, inaccordance with the needs of the pedicle screw design improvements, useCAD software to draw.Results and conclusions: preliminary design the anterior pediclescrews supporting plate and the professional set staple removers.