Research Of The Accuracy Of Computer-Assisted Cervical Pedicle Screw Installation

PartⅠ:Disccusion of the accuracy of computer-assisted cervical pedicle screw installationObjective:Because of the superiority of three columns fixation, cervical pedicle screw fixation should have good prospects.However, cervical pedicle has variable anatomic structure and complex adjacent tissues.The potential risk to injury adjacent neural and vascular tissue is great.So it is the key point to increase the accuracy of screw insertion and decrease the incidence of screw's malposition. Computer-assisted navigation,also named as computer-assisted surgery (CAS),can put the anatomical structure and the surgical instrument in operation into the same space.So a dummy three-dimensional display visible on the screen can be required,which can directly guide the manipulation and theoretically increase the accuracy.The purpose of this study is to evaluate the accuracy of computer-assisted cervical pedicle screw installation by clinical practice.Method:Under general anesthesia,25 patients including cervical spine injury in 12 patients,cervical myelopathy due to kyphosis or instability in 11 patients,cervical spondylotic radiculopathy in 1 patient,and ossification of the posterior longitudinal ligament in 1 patient were placed prone.Cervical spine was maintained in a neutral position by neck fixed with Gardner-Wells skull traction or Mayfield 3-pin skull frame.A midline incision was made and cervical laminaes were exposed to the edge of both lateral masses.With the maintenance of proper cervical alignment,a reference frame was fixed on spinous process,and lower cervical spine was scanned at 1-mm interval using CT-SIREMOBIL Iso-C 3D(German),and the data were transferred to the computer workstation of the image-guiding system (infrared-inducing navigation system,Stryker corporation) to reconstruct a three-dimentional image visible on a monitor screen. Registration of the vertebra is done using the surface matching algorithm,where a predicted accuracy of＜1.0mm was accepted.If the predicted accuracy was＞1.0 mm,we repeated the registration procedure until we reached an accuracy of＜1.0 mm.After registration of the vertebra,verification was done to ensure that the virtual reality of computer-assisted image guidanc system corresponded to the surgical reality.If verification is accurate,the navigated instrumentation can begin;otherwise the entire registration procedure must be repeated.A total of 144 cervical pedicle screws were installed by computer-assisted navigation.According to the standard:whether or not there is screw perforation and the degree of perforation,cervical pedicle screw's position is divided into three groups:Group 1:correct screw placement without pedicle perforation or pedicle perforation＜1mm.Group 2:pedicle perforation＞1mm without the need for screw revision,without symptom of surrounding tissue,with stable internal fixation.Group 3:pedicle perforation＞1mm with the need for screw revision due to irritation or injury of roots or the myelon or due to reduced biomechanical stability.All the patients were examined by X-rays and CT after operation. Screw's position and direction were measured on the sagittal and transectional image of intraoperative navigation and post-operative CT. Statistical difference was determined by t test(SPSS 11.5) for group comparison.Result:A total of 144 screws were inserted from C3 to C7.Two screws perforated the upper pedicle wall,3 deviated from the lateral pedicle wall.Among the total of 144 screws,there were 139 screws in Group 1,3 screws in Group 2,and 2 screws in Group 3.The accurate rate of cervical pedicle screw placement with computer-assisted navigation is 96.5%(139/144).The position and angle of 121 screws in transectional image were analyzed.The position and angle of 99 screws in sagittal images were analyzed.No significant difference was seen between navigation images and post-operative images.No change in screw position had been found after 3 months follow-up.Conclusion:Computer-assisted navigation can improve the accuracy of cervical pedicle screw installation.Intraoperative navigation images can show screw's direction and position accurately,and screw's direction and position in post-operative CT images can reflect screw's direction and position in intraoperative navigation images. PartⅡ:Analysis of errors of computer-assisted cervical pedicle screw installationObjective:Although a CAS system is a useful and fascinating tool for spine surgery,any spine surgeon using such a intraoperative instrument should be aware of its possible errors.The purpose of this study is to analyze the reasons of screw malposition by clinical practice.Method:Under general anesthesia,25 patients including cervical spine injury in 12 patients,cervical myelopathy due to kyphosis or instability in 11 patients,cervical spondylotic radiculopathy in 1 patient,and ossification of the posterior longitudinal ligament in 1 patient were placed prone.Cervical spine was maintained in a neutral position by neck fixed with Gardner-Wells skull traction or Mayfield 3-pin skull frame.A midline incision was made and cervical laminaes were exposed to the edge of both lateral masses.With the maintenance of proper cervical alignment,a reference frame was fixed on spinous process,and lower cervical spine was scanned at 1-mm interval using CT-SIREMOBIL Iso-C 3D(German),and the data were transferred to the computer workstation of the image-guiding system (infrared-inducing navigation system,Stryker corporation) to reconstruct a three-dimentional image visible on a monitor screen. Registration of the vertebra is done using the surface matching algorithm,where a predicted accuracy of＜1.0mm was accepted.If the predicted accuracy was＞1.0 mm,we repeated the registration procedure until we reached an accuracy of＜1.0 mm.After registration of the vertebra,verification was done to ensure that the virtual reality of computer-assisted image guidanc system corresponded to the surgical reality.If verification is accurate,the navigated instrumentation can begin;otherwise the entire registration procedure must be repeated.A total of 144 cervical pedicle screws were installed by computer-assisted navigation.According to the standard:whether or not there is screw perforation and the degree of perforation,cervical pedicle screw's position is divided into three groups:Group 1:correct screw placement without pedicle perforation or pedicle perforation＜1mm.Group 2:pedicle perforation＞1mm without the need for screw revision,without symptom of surrounding tissue,with stable internal fixation.Group 3:pedicle perforation＞1mm with the need for screw revision due to irritation or injury of roots or the myelon or due to reduced biomechanical stability.All the patients were examined by X-rays and CT after operation. Screw's position and direction were measured on the sagittal and transectional image of intraoperative navigation and post-operative CT. Statistical difference was determined by t test(SPSS 11.5) for group comparison.Result:A total of 144 screws were inserted from C3 to C7.Two screws perforated the upper pedicle wall,3 deviated from the lateral pedicle wall.There was no statistical difference in screw's position and direction between navigation image and CT image.Among the total of 144 screws,there were 139 screws in Group 1,3 screws in Group 2,and 2 screws in Group 3.Navigation image is based on the principle of rigid tissue.However,the characteristic of cervical operation will not fit for the principle entirely.The relative shift of the object's anatomic position in three-dimensional space is intituled "the excursion phenomenon".Conclusion:The excursion phenomenon is responsible for screw's malposition.Only by understanding the navigational principle and the characteristic of cervical spine's operation,together with personal experience,we can make good use of CAN.