Imaging Analysis Of Ponticulus Posticus And Its Effect On Selection Of Pedicle Screw Insert Channel

Background:The ponticulus posticus is a common variation of atlas,the altered anatomy of the atlas may affect the insertion of the atlas pedicle screw,decrease the stability as well as the increasing chance of complication after the operation.Objective:Rebuilt patient‘s three-dimensional CT imaging data,calculate the rate of four types ponticulus posticus,analyze its epidemiological characteristics,imitate and measure the screw trajectory locate,analyze the influence of ponticulus posticus on the selection of pedicle screw insert location and direction.Methods:Analysis the imaging data of patient’s cervical CT examination of our hospital from March 2021 to October 2021,according to which perform three-dimensional digital multiplanar reconstruction.Observed ponticulus posticus anatomical morphology,measured and recorded the height（H）and width（D）of the I,II,III,IV four types of the vertebral artery groove posterior arch,selected the suitable patient of pedicle screw insertion.Rebuilted their’s three-dimensional CT imaging data,measured the largest medial and lateral angle of inclination（α、β）,the maximum and minimum distance of entry point and the midline（L~1,L~2）,the distance from the entry point to the upper and inferior border of the posterior arch（D~1,D~2）,the head inclination angle of atlas pedicle screw（δ）.Measurements were statistically analyzed to explore the probability of occurrence and statistical difference of variations of posterior ring of each kind of ponticulus posticus,and the optimal pinning point and angulation of pedicle screw were calculated from the measured data,and figured out the statistical analysis.ResultA total of 550 patients were enrolled in the study,including 338 males and 212females,There were 181 cases of ponticulus posticus16.5%（181/1100）,113 patients with ponticulus posticus 20.6%（113/550）,The ponticulus posticus probability is 20.6%in the statistical population,of which the probability is much higher in male than that in female（P<0.05）.The incidence of ponticulus posticus between left and right vertebral artery sulcus was no significant difference（P>0.05）.The height of the type I ponticulus posticus variation vertebral artery groove posterior arch was4.76±1.06mm,of which the type II,III,IV were 4.81±0.75mm、4.04±0.69mm、3.89±0.58mm.selected the suitable patient of pedicle screw insertion.Rebuilted their’s three-dimensional CT imaging data,the largest medial and lateral angle of inclination（α、β）,the maximum and minimum distance of entry point and the midline（L~1,L~2）,the distance from the entry point to the inferior border of the posterior arch（D~2）,show no significantly difference between I,II,III,IV four types（P>0.05）,The distance from the entry point to the upper border of the posterior arch（D~1）and the head inclination angle of atlas pedicle screw（δ）showed statistically significant difference（P<0.05）.The ideal entry point and screw trajectory of this studyγ、L~3、D~1、D~2、δwas 8.78±3.48°、20.45±1.70mm、5.64±1.54mm、2.80±0.76mm、5.66±2.80°.Conclusion:The ponticulus posticus variation rate is 16.5%,probability is 20.6%in the statistical population,of which the probability is much higher in male than that in female.Patients with with type I,II,III variant of ponticulus posticus are suitable for pedicle screw insertion（3.5mm）.The pedicle screw insertion was not recommended with the patients with typle IV ponticulus posticus.The ideal entry point and screw trajectory:the ideal angle of inclinationγwas8.78±3.48°,the ideal distance of entry point and the midline（L~3）was 20.45±1.70mm,the distance from the entry point to the upper and inferior border of the posterior arch（D~1 D~2）was5.64±1.54mm and2.80±0.76mm,the head inclination angle of atlas pedicle screw（δ）was 5.66±2.80°.