Objective     To evaluate 64-slice CT scaning in prone position and improved measurements of pedicle parameters to guiding accurately the pedicle screws placement in adolescent idiopathic scoliosis (AIS).     Methods      Twenty-one patients with AIS who admitted in our hospital from January 2009 to June 2010 were enrolled in this study. They were 8 males and 13 female at a menaing age of 15.2 (ranging from 6 to 18.8). All patients underwent preoperatively 64-slice CT scaning in prone position. On the reconstructed CT images

3 dimentional localization of pedicle entry point

the width of pedicle spongy bone and the sagittal angle were measured in addition to the traditional pedicle parameters (pedicle inclination angle

pedicle depth and vertebral rotation angle). The pedicle screws insertion was guided by the improved pedicle parameter measurements. Postoperatively

low dose CT scanning was performed to evaluate the accuracy of pedicle screw placement and the Cobb’s angle.     Results      A total number of 226 screws were inserted into the pedicles

in which 5 (2.2%) were displaced

and 221 were within the safe zone with an accuracy rate of 97.8%. No pedicle expansion or intervertebral disk injury was found. The Cobb’s angles were corrected to 2°  to 58.3°  (mean 15.6°) from preoperative 42.2°  to 112.3°  (mean 62.1°).      Conclusion      Prone 64-slice CT scanning and modified pedicle parameter measurements can improve the accuracy of pedicle screws placement in AIS

and should be applied widely in clinical practice.