| Part.1:Imaging study on the morphology of odontoid process during pediatric growth Background:As an important part of the craniocervical junction,the growth of the axis would not be ceased until the age of 25.There were significant morphological differences between the axis and other cervical vertebrae because of the odontoid process.Although there were many studies on the odontoid process,most of them described and analyze the morphology and imaging of adults or the therapeutic analysis of some diseases for the odontoid process.There was sparse literature on odontoid morphology in the growth of children.Purpose:Through the measurement of the imaging parameters of the odontoid process in children,we hoped to find the relationship between the imaging parameters of the odontoid process and the growth of children.Method:The cervical spine CT of healthy children were retrospectively collected.After importing the software,the median sagittal plane of the odontoid process were obtained:the anterior edge angle of the odontoid process,the posterior edge angle of the odontoid process,the odontoid retroflexion angle,the posterior dens angulation angle(PDAA),the screw insertion angle of the odontoid process(SIA),the line of p B-C2(perpendicular basion-C2),the height of odontoid process,the height of axis vertebra and the screw insertion length of odontoid process(SIL)were measured.Then adjust the plane to obtain the cross-section of the inferior edge of the odontoid process: the anterior-posterior diameter of the inferior edge of the odontoid process,the transverse diameter of the inferior edge of the odontoid process,and the area of the inferior edge of the odontoid process were measured.Result:In the imaging measurement of the odontoid process,it was found that all the measurement parameters had no significant difference between different sex.Except that there was no significant change in the screw insertion angle of the odontoid process in pediatric growth,the other angle parameters decreased with age.The height of the odontoid process,the height of the axis vertebra,the screw insertion length of the odontoid process,the anterior-posterior diameter,and the area of the inferior edge of the odontoid process would increase with age,but the tendency to increase would slow down after 13 years old.The p B-C2 line gradually increased from birth to a peak at 12 years old,and then slowly declined to adulthood.On the cross-section,the transverse diameter of the inferior edge of the odontoid process remained stable after 6 years old.Conclusion:In this study,it was found that the odontoid process was retroflexion as children grow,the inclination of the posterior edge of the odontoid process was more obvious than the anterior edge,while the height of odontoid process,the screw insertion length and the height of axis vertebrae were increasing with age.The transverse diameter of the inferior edge of the odontoid process remained stable after 6 years old,but the anterior-posterior diameter continued to increase until adulthood.However,these changes declined gradually until adulthood after the age of 13.Part.2:Comprehensive analysis of axial pedicle screw placement in children using computed tomography-based three-dimensional modelsBackground:The instability of atlantoaxial joint caused by trauma,tumor,deformity and degeneration of upper cervical spine have been bring catastrophic consequences to patients.Therefore,posterior C1 lateral mass and C2 pedicle screw fixation have been widely used to treat upper cervical instability.However,the technical requirements for pedicle screw placement were extremely high because the upper cervical vertebra was close to the skull base.Many scholars measured the axial pedicle to standardize the parameters of axial pedicle screw placement in order to reduce the complications during instrumentation.However,most of these studies were aimed at adults,and there were very spare literatures on the feasibility of pedicle screw fixation in children,or only a very small amount of axial CT were measured to obtain the results.Moreover,there are few specific studies on the parameters of C2 pedicle screw fixation in children.Purpose:The reconstructed children’s 3D axial digital models were used to simulate the placement of axial pedicle screws in the software,to determine the ideal entry point and ideal trajectory parameters of axial pedicle screws.Method:The CT images of pediatric cervical spine were retrospectively collected to reconstruct the 3D digital models of cervical spine and separate the axis,then,the pedicle screws were simulated and implanted in the software to determine the ideal entry point and trajectory.The pedicle screw length,pedicle diameter,lateral angle and sagittal angle were measured.In addition,taking the lateral notch as the origin,the coordinate system was determined to measure the LN horizontal distance and LN vertical distance of the ideal entry point on the surface of the lateral mass.At the same time,coordinate system is determined by the most inferior point of the lateral mass surface and the most lateral point of the lateral mass surface,and the horizontal distance and vertical distance of the ideal entry point are measured respectively.Then,all the measured data were analyzed between different ages,sex and sides groups.Result:In the analysis of 214 pedicles in 107 children,it was found that the pedicle diameter and the screw length were 6.02 ±1.31 mm and 25.63 ±3.46 mm,respectively.There were significant differences in pedicle diameter and pedicle screw length between sex.The ideal entry points gradually moved to medial and slightly caudal with the growth when they were depicted by LN horizontal distance and LN vertical distance on the surface of lateral mass.When drawed the ideal entry point with horizontal distance and vertical distance,the entry point gradually migrated to medial and cephalad with ages.Conclusion:In this study,it was found that the parameters of pedicle screw placement were different based on sex,ages and laterality pedicle,and the ideal entry point was distributed linearly on the surface of lateral mass with growth.These results of pedicle screw placement studies on the axis are of great help in the pediatric patients to surgeon to facilitate operation. |
