The Application Anatomic Of Thoracic Pedicle And Pedicle Rib Complex And Biomechanical And Clinic Evaluation Of Associated Internal Fixation Technique

Posterior transpedicular screws fixation produced a three-pointfixation and offered a best biomechanical stability. However， thetranspedicular screw technique is technically demanding and requiresconsiderable experience. Because the thoracic pedicle is thinner thanlumbar pedicle anatomically，and the spinal cord is in the thoracic spinalcanal，transpedicular screw fixation in thoracic spine is more dangerousand difficult than lumbar spine，complications as neural-vascular injuryis encountered sometimes. Particularly in some cases of scoliosis orother spine deformity，the morphology of pedicle deformed seriously andthe anatomic relationship between pedicle and around structures alsochange， it is much more dangerous and d1fficult in placingtranspedicular screw in this situation.The extrapedicular method ofcosta-transverse approach offered a good fixation method for thoracicposterior fixation，it is safer than transpedicular method and possessmuch advantages. But the costa-transverse method is withoverelaborated penetration angle and difficult to presided，particularly，absence systematic study of anatomy and biomechanics and clinics evaluation. This study aimed to set up a new systematic extrapediculartechnique method for thoracic spine posterior fixation，and evaluated thepresent technique from anatomy，biomechanics and clinics.PART Ⅰ THE ANATOMY IN THE THORACIC SPINE ANDBIOMECHANICS IN PEDICLE SCREWObjective To establish the bone mark and safe area for the thoracicpedicle screw insertional point through the anatomic morphologicfeatures study of thoracic pedicles. According to the biomechanicalstudy on the different orientation point and direction of the pedicle screwfixation technique, a kind of convenient, exact and new technique forthoracic pedicle screw fixation was developed to increase the accuracyof operation, apply to clinic and decrease the risk and its complicationsof the operation to the greatest extent. Furthermore, the new techniquewill be spread in favor of application.Methods Thirty specimens of dry thoracic vertebrae were performed tomeasure the anatomy parameter of the thoracic pedicle and determinethe bone mark and safe area of the thoracic pedicle screw fixation. Twotechniques (Straight-forward versus along pedicle anatomic trajectorytechnique) were compared in the biomechanical analysis of the accuracyand the pullout strength of screw placement from6specimens of freshthoracic vertebrae.Results The bone mark and safe area of the pedicle screw insertionalpoint were determined through the morphologic features study ofthoracic pedicles. The straight-forward technique, the insertional pointand direction of the thoracic pedicle screw along trajectory techniquewere definited. There was no significant difference between the thoracicvertebrae along pedicle trajectory technique and the pullout strength ofthe utmost axial direction of the pedicle straight-forward technique. Conclusion The fixation of thoracic vertebrae along pedicle anatomictrajectory is a safe, reliable, accurate and new technique. The findingssuggest that it should be applied to clinic and decrease the risk andcomplications of operation to the greatest extent.PARTⅡ PULLOUT STRENGTH OF PEDICLE RIB COMPLEXSCREWS VERSUS OEDICLE SCREWS IN THETHORACIC SPINEObjective To study applied anatomy of the pedicle and the pedicle–ribcomplex and biomechanical test for placement of screw insertionthrough pedicle–rib complex in the thoracic spine. A kind of convenient,exact and new technique for thoracic pedicle screw fixation wasdeveloped to increase the accuracy of operation, apply to clinic anddecrease the risk and its complications of the operation to the greatestextent. Furthermore, the new technique will be spread in favor ofapplication.Methods Six specimens of fresh adult cadaveric thoracic spine wereused to observe modality of pedicle and pedicle–rib complex.Measurepedicle width (P-W),pedicle height (P-H), pedicle length (P-L), pediclesagital angle (P-SA), pedicle lamina angle (P-LA) and the pedicle–ribcomplex transverse distance (PRC-W), longitudinal distance (PRC-H),screw length (PRC-L), argulation in sagittal plane (PRC-SA) and inlamina plane(PRC-LA). From T1to T12segments of6cadavericspecimens were used to imitate operation, pedicle screw, pedicle–ribcomplex screw were placed respectively to measure the maximum axialpull–out strength (F–max).Results PRC-W：13.0～17.3mm, PRC-H5.8～8.0mm, PRC-L43.4～60.5mm, PRC-SA15.4°～36.7°，PRC-LA76.2°～85.4°. In pedicle： F-max was703N，in pedicle rib complex：F-max was685N. There wereno significantly statistical differences between the two groups(P＞0.05).Conclusion Placement of pedicle–rib complex screw in thoracic spine issafer and has better mechanical stability than that of pedicle screw. Thepull-out strength of pedicle rib complex screw was in inferior positioncompared with the pedicle screw，so the former may be just regarded asa supplementary of the latter in some instance such as the transversalwidth of thoracic pedicle was too little to screw.PART Ⅲ CLINLCAL STUDY OF PLACEMENT OF PEDICLESCREWS FOR SCOLIOSIS BASED ON3DNAVIGATION SYSTEMObjective To evaluate the risks of the transpedicular technique and thefeasibility and advantages of the extrapeieular technique by observatingmorphology of the pedicle and other structures of scoliosis patients withCT.Methods11cases of scoliosis were analyzed by CT scanspreoperatively， observation include morphology of pedicle andpedicle-rib complex，rotation of vertebral body，and the around importantblood vessel or other soft tissue. We targeted these cases in whichsegmental pedicle screw fixation had been performed using a navigationsystem. Evaluate the screw place and the effect postoperatively and thento assess the clinic value of the extrapedicular technique.Results Vertebrae morphology of scoliosis cases：(l)concave side pediclethinner than convex side，the thinnest we found one is less than0.8mm.the convex side pedicle is windy changing，the vertebrae body iswedging changing and trend to concave side. The spinal cord pressed close to the concave side pedicle，and deviated to the convex sidepedicle.(2) The artery located laterally and back on the vertebrae body.In terms of screw deviation，25(19.8%)of the126inserted screws wereclassified as total deviation. However, there were no neurovascularcomplications during or after surgery in any cases， and all casesmaintained strong internal fixation.Conclusion The width or morphology of pedicle or other structures werea11changed in the cases of scoliosis，pedicles which were too thinner orserious deformity and not suitable to be fixed with tranpedicularmethod，should be using extrapedieular fixation technique，it is well usedin these cases，and no neurovascular complication.