Study Of Cervical Lateral Mass Screw Fixator

Objective: In accordance with the anatomic features of the cervical spine of Chinese people, design a new type of cervical lateral mass screw fixator. Backgrounds: It was needed to reconstruct the stability of the cervical spine in lower cervical fractures and dislocations, post-expansive laminectomy in severe degenerative diseases and tumors. But it was confirmed that pure anterior bone implantation and anterior plate fixation could not achieve effective stability in posterior cervical structure injuries. Among posterior cervical flxators, the process wire and the interlaminar clamp need the posterior cervical structures keep intact, the use of them is limited and their fixation effects are unreliable. The lateral mass screw technique does not need the process and the lamina keeps intact and its fixation effect is reliable. But in operation, this technique need some experiences and may have some dangerous. The cervical pedicle screw technique is too dangerous. The cervical lateral mass screw plate has already been used abroad, but its safety, easy of operation and biomechanical features have some defects. The use of them in domestic is limited, and it is worth to improve on. Methods: In order to give consults to the designing of the new type cervical lateral mass screw fixator and the new operation methods, measurements were done on 35 dry cervical vertebral samples and 100 cervical X-ray films and CT films to get anatomic and imaging parameters of the lower cervical posterior structures of Chinese people. On the basis of the anatomical study, directing to the problems of now available cervical lateral mass screw plate systems, a new type of cervical lateral mass screw fixator and a new cervical lateral mass screw implant technique were designed. The new type cervical lateral mass screw fixators were implanted into five fresh cervical samples, and the three dimensional stability and rigidity were tested using the spinal three dimensional motion testing system and the material testing machine. The constructs were the cervical process wire, the cervical lateral mass screw plate, and the cervical pedicle screw plate. The screw pull-out strength of the new cervical lateral mass screw technique, the cervical lateral mass Roy-Camille technique, Magerl technique, and the cervical pedicle screw technique were tested using the material testing machine. The screws were implanted into five fresh cervical samples using the new cervical lateral mass screw technique, the cervical lateral mass Magerl technique, and the cervical pedicle screw technique imitating operative situation. The screw positions were evaluated by the X-ray and CT 4 filIns tO defor the accuracy and safety of the ecbo haPlantation tecboques. ReSult8:Ih the new tw cervical larend mass screw fixator, the diamatr of the screw shouldbe 3.5 nnn, the length should be l4~l8 nun. The diStane between screws shouId beadjuStale and the nail-stick Strutw was used. In the new cervical lateral mass screwimPlan technique, the diStalle of the screw eine point to the lateral and inferiorof the lateral mass should be 2 rnm. The implat direction should be 40" ~50"medial and 40" cephalad, directed to the pedicle, and ethece to the connection ofthe lateral mass and the Pedicle. Biomechanical tests show tha the stabiliZaion to theMle cervical spine due tO posterior structure injUry and the rigidity of the newcervical lateral mass screw fixator were equal to the traditional cervical latCtal massscrew plate, superior to the cervical process wire and inferior to the cervical Pediclescrew plate. The screw Pull-out strength of the new...