Objective To observe the imaging features of partiallythreaded screw fixation using in various kinds of C2 pedicel fracture.Methods CT image materials of 160 Chinese Han patients who suffered from atlantoaxial injury without vertebral body and pedicle fracture of C2 was included in this study,including 120 males and 40 females.Pedical trajectory selected according to Ebraheim method in threedimensional CT reconstruction was analyzed in ADW 4.4 workstation.The posterior wall fracture of C2 vertebral body,isthmus fracture and fractures under C2 laminar were simulated according to clinical observation.The trajectory length (partiallythreaded screw length) from entry point to anterior cortical bone of C2,bolt shank length from entry point to fracture line and fillet of screw length from fracture line to anterior cortical bone of C2 were measured.Relations between height,gender and partiallythreaded screw length bolt shank and fillet of screw length was evaluated.Results Male height was 167±7.9 cm on average,and female was 156±6.6 cm.The length of partiallythreaded screw was 29 mm in male and 25 mm in female on average.Height and gender was positively correlated with partiallythreaded screw length.In posterior wall fracture of C2 vertebral body,length of bolt shank was an average of 17 mm in male and 15mm in female,while fillet of screw length was 12 mm in male and 10 mm in female.The mean length of bolt shank was 14mm in male and 13 mm in female,while mean fillet of screw length was 15 mm in male and 12 mm in female in isthmus fracture.In fractures under C2 laminar,length of bolt shank was 10 mm in male and 9 mm in female on average,while mean fillet of screw length was 18 mm in male and 15mm in female.Conclusion The length of partiallythreaded screw used in posterior axial pedicle fracture may have a close correlation to length and height.The length of bolt shank and fillet of screw was different according to the position of the fracture.