Spinal pedicle fixation. Confirmation of an image-based technique for screw placement

Although many advances in the technique of pedicle screw insertion have been made, there still exist unacceptable rates of perforations through the pedicle cortex. Successful placement of a pedicle screw requires accurate identification of the entry point, correct transverse and sagittal plane angulation, safe preparation of a pilot hole, and appropriate depth of insertion. The authors propose that a technique of pedicle screw insertion using posteroanterior image intensification angled in the axis of the pedicle to define the entry point and guide insertion would improve the accuracy of this procedure. This study tests the accuracy of pedicle screw placement using this technique. Ninety pedicle screws were placed in human cadaveric lumbar spines. All specimens were then dissected and split longitudinally to assess accuracy of pedicle insertion by both visual and palpatory means. Five of 90 (5.5%) pedicle screws were found to have perforated the pedicle. Three of these were at L1, two of which were due to the transverse pedicle diameter being smaller than the screw diameter. Therefore, a 3.4% incidence of pedicle perforation due to malpositioning and a 2.1% incidence of pedicle perforation secondary to pedicle/screw size discrepancy was determined. This technique may lead to significant improvements over recently reported rates of pedicle screw perforations; however, this in vitro condition eliminated many potentially complicating factors that might be encountered in the clinical setting.