An Imaging Analysis Of Ponticulus Posticus And Its Effect On Pedicle Screw Insertion

Background:The ponticulus posticus is a common anatomical variation of the atlas,which may affect the insertion of the atlas pedicle screw through the posterior arch,resulting in vertebral artery injury.Objective:To calculate the incidence of ponticulus posticus,and analyze its epidemiological characteristics.To measure the height and width of the posterior arch of the vertebral artery based on three-dimensional CT imaging data,and analyze the influence of ponticulus posticus on pedicle screw insertion.Methods:Retrospective analysis of imaging data of patients undergoing cervical CT examination from November 2017 to October 2018 in our hospital,and performed three-dimensional digital multiplanar reconstruction.Observed the morphology of atlantoaxial vertebral artery groove.Measured and recorded of the height(H)and width(D)of the posterior arch of the vertebral artery groove.Analyzed epidemiological characteristics and classification of ponticulus posticus.To calculate the incidence and difference of bilateral ponticulus posticus,and make statistical analysis.Result:A total of 500 patients were enrolled in the study,including 227 males and 273 females.There were 128 cases of ponticulus posticus.The incidence rate was 25.6%(128/500),of them,the incidence rates of male and female were 31.7%(72/227)and 20.5%(56/273).The incidence of ponticulus posticus in male was significantly higher than that in women,and there was statistically significant difference(P < 0.05).In the ponticulus posticus,including 13 cases of bilateral complete type(2.6%,13/500),25 cases of bilateral partial type(5.0%,25/500),13 cases of unilateral complete type(2.6%,13/500),64 cases(12.8%,64/500)with one-sided partial type.There was no significant difference in the incidence of ponticulus posticus between the left and right vertebral artery sulcus(P > 0.05).The height of posterior arch at the bottom of the vertebral artery groove: no ponticulus posticus variation was(4.56 ± 0.79)mm,ponticulus posticus variation was(3.59 ± 0.70)mm,there was statistical significance between them(P < 0.05),of which the typle I,II,III,IV were(4.33 ± 0.76)mm,(3.59 ± 0.53)mm,(3.35 ± 0.45)mm,(3.14 ± 0.32)mm.The width of posterior arch at the bottom of the vertebral artery groove: no ponticulus posticus variation was(9.19 ± 1.06)mm,ponticulus posticus variation was(9.09 ± 1.11)mm,there was no statistical significance between them(P > 0.05);of which the typle I,II,III,IV were(9.17 ± 1.87)mm,(9.18 ± 1.07)mm,(9.04 ± 1.15)mm,(8.98 ± 1.22)mm.Conclusion:The incidence of ponticulus posticus is higher,which is more common in male.The height of the posterior arch at the bottom of the vertebral artery groove which has ponticulus posticus is lower than that without it.There was little influence on the pedicle screw insertion(Diameter of 3.5 mm)when patients without ponticulus posticus or with type I ponticulus posticus.Pedicle screws can be inserted in pedicles when the patients with type II ponticulus posticus,but the risk is greater.The pedicle screw insertion was not recommended when the patients with typle III-IV ponticulus posticus.The preoperative CT examination and digital reconstruction of 3D CT can help to determine the location and classification of mutations.Measuring the height of the posterior arch at the bottom of the vertebral artery groove can help the surgeon to design a personalized pedicle screw fixation method to avoid complications,such as vertebral artery injury.