Anatomy And Imaging Study On Atlantoaxial Of Children And Clinical Application Of Pedicle Screw Fixation

ObjectiveNow most study concerning on this technique was about adults,there was no anatomic and imaging study of the posterior pedicle screw fixation on atlantoaxial of children at home and abroad.From anatomic and imaging study,we aimed to explore the feasibility of posterior pedicle screw with 3.5mm diameter fixation on the atlantoaxial of children(6-8 years old),and evaluated the present technique from clinics.Including:1,To measure the anatomic and imaging data,finding the proper entry point and pedicle path,then to evaluate the feasibilty of inserting a pedicle screw with 3.5mm diameter on C_1,2 of children who were between 6 and 8 years old.2,After failure conservative treatment,we used atlantoaxial pedicle screws to treat atlanto-axial dislocation,to test and verify the reliability of screw placement technique.Clinic application,evaluating,testing and verifying the reliability of the C_1,2 pedicle screw placement technique on the patients.Materials and methods1,Ten children's cadaveric specimens were dissected to get their atlantoaxial vertebral, and the following parameters were measured or evaluated,including the:â‘ the height and width of the C_1,2 pedicle:â‘¡setting the entry point of C_1,2 pedicle screw;â‘¢with statistical analysis,to evaluate the feasibilty of inserting a pedicle screw on C_1,2 of children.2,CT axial scanning were performed in 20 children,who were suspicion of upper cervical vertebra damaging,after 3-D imagery,measuring the height,width and length, through data statistical analysis,to evaluate the feasibilty of inserting a pedicle screw on C_1,2 of children.3,In 5 patients with atlanto-axial dislocation,after failure conservative treatment,3.5 mm pedicle screws were placed on atlantoaxial.The path of C_1,2 screw was assessed on postoperative radiographs and CT scans,to test and verify the reliability of screw placement technique.Results1,The results of anatomic measurements:â‘ the average height and width of the C₁ pedicle was 5.20mm and 6.20mm respectively,the middle height of atlas lateral mass was 9.96 mm,the middle width of atlas lateral mass was 10.10mm,the width of C₁ posterior arch under the vertebral artery groove was 6.98mm,the height of external one-third of C₁ posterior arch under the vertebral artery groove was 4.04 mm,the height of internal one-third of C₁ posterior arch under the vertebral artery groove was 3.68mm;â‘¡the external and interal height of C₂ pedicle was 6.83mm and 6.64mm respectively,the superior,mid-portion and inferior width of C₂ pedicle was 6.59mm,5.36mm and 3.76mm respectively;â‘¢the trajectory angle of C₁ pedicle screw was 5.5°in a cephalad direction,10.5°in a medial direction;the trajectory angle of C₂ pedicle screw was 32.3°in a cephalad direction,27.3°in a medial direction.2,The results of imaging measurements:â‘ the average height of the C₁ was 5.49mm, the average width was 6.61mm;â‘¡the average height of the C₂ was 6.57mm,the average width was 6.11mm;â‘¢the average angle of C₁ and C₂ pedicle between axis and midsagittal was 9.55°,28.05°.3,Twenty C_1,2 pedicle screws were placed exactly in five patients(five patients in both sides),and no neural or vascular injury was observed.There was no case of implant failure; all the cases had a solid fusion on radiographs after 3 to 6 months.Conclusion1,Through the study of anatomy and imaging,it is possible to insert a pedicle screw with 3.5mm diameter on C_1,2 of children,who are between 6 and 8 years old,the clinical use also proves the possibility and suitability of pedicle screw fixation on C_1,2.2,The technique of insert C_1,2 pedicle screws on children:â‘ the entry point of C₁ is 18mm to the posterior midline,3.0mm inferior to the superior of C₁ posterior arch,the trajectory angle of C₁ pedicle screw is 5°in a cephalad direction,10°in a medial direction;â‘¡the entry point of C₂ is 20mm to axis spinous process,7.0mm superior to the inferior of axis under facet,the trajectory angle of C₂ pedicle screw is in a cephalad direction 32°,in a medial direction 27°;â‘¢The average length of C₁ pedicle screw was 24mm,the average length of C₂ pedicle screw is 21 mm.