Studying The Relationship On The Horizontal Distance From Atlas Pedicle Screw Entry Point To Medial Border Of Atlas Pedicle

[Objective] In order to establish an atlas pedicle screw placement positioningtechnology with the medial border of atlas pedicle as an anatomical landmark, thecross-sectional of atlas pedicle was scanned by CT to determine the positionparameters between the entry point and the border. In the further step, this techniquewas evaluated by clinic application.[Methods] Radiographic Assessment: From April2010to December2010,50atlasCT images of normal adults（including25males and25females）were selectedrandomly to measure the horizontal distance from atlas pedicle screw entry point tomedial border of atlas pedicle by our method (including0°insertion angle and10°insertion angle).The date was statistically analyzed and indicated a differencebetween male and female．2、Clinical application: Five cases with operative indicationwere treated with posterior internal fixation of atlantoaxial pedicle screw fromDecember2010to February2012．All of these atlas pedicle screws operations wereaccording to our established surgical standard. Of all of these five cases, four had oldodontoid fracture, one had fresh odontoid fracture. All patients had varying degrees ofatlantoaxial dislocation. These operations were simulated in the CT imagines and during the operation, the patients were monitored for complications. Screw positionwas lately determined by CT scan. All of these patients were followed up for6to12months. Internal fixation and bone graft fusion were assessed by radiographicimaging.[Results]1、Radiographic assessment: At0°insertion angle the horizontal distancewas（4.78±0.62）mm for male while it was（3.88±0.56）mm of female. There wassignificantly different between them（P<0.01）； at10°insertion angle it was（6.62±0.70）mm of male bu（t5.19±0.59）mm of female, with significantly differencebetween them（P<0.01）.2、Results of clinical application:Ten atlas pedicle screwswere placed exactly in five patients and no neural or vascular injury wasobserved．The postoperative radiographs verified all of these atlas screws was placedwell．No internal fixation loosening or breakage cases were found during follow-upand all of the atlantoaxial got good bone graft fusion after an average period of6~7months.[Conclusions] The medial border of atlas pedicle could be as a convenient anatomiclandmark to determine the position of atlas pedicle screw entry point，and thelandmark is more invariant comparing with the previous anatomical ones．thistechnique should be referred to the private scanning imagine, because there aredifference of interval between the medial border of atlas pedicle and the screw entrypoint from women to men.