Cervical pedicle screw insertion using a computed tomography cutout technique

Abstract

The pedicle screw has been reported to provide the strongest fixation for the cervical spine, but there is a possibility of malpositioning the screws, which may cause fatal complications such as vertebral artery and neural injuries. Using the conventional freehand technique, between 6.7 and 29% of the screws have been found to be malpositioned. If an accurate entry point and insertion trajectory through the isthmus of the pedicle can be maintained during surgery, safer insertion of the pedicle screw should be achieved. The authors have developed a new pedicle screw insertion method, called the "CT cutout" technique, and report on the technical and clinical aspects of this new technique in terms of accuracy. A total of 130 pedicle screws were inserted from C-2 to T-1 in 29 consecutive patients using the new technique. In the CT cutout technique, a CT slice of every vertebra in which the authors intended to insert pedicle screws was captured from 3D CT images of the cervical spine with the gantry parallel to the pedicle. A life-sized CT image was developed for each level, and the desired insertion line, passing through the middle of the isthmus, was drawn on the image. The images were then cut along the insertion line and the posterior margin of the lamina, and sterilized. During surgery, the proper cephalocaudal entry point was determined using a lateral fluoroscopic image, the CT cutout was placed on the posterior surface of the lamina, and the appropriate entry point and trajectory of pedicle screw insertion were chosen with reference to the CT cutout. The percentage of malpositioned pedicle screws and the deviation between the intended entry point and angle of the pedicle screw, and those that were achieved in practice, was investigated using postoperative CT images. Three perforations (2.3%) in which more than half a screw diameter was exposed outside the pedicle, and 2 penetrations (1.5%) in which a screw diameter was completely exposed, were identified on the postoperative CT images. All breaches were directed laterally. No neural or vascular injuries were observed. The deviation between the intended entry point and angle of the pedicle screw and the actual values was 0.20 +/- 0.75 mm and 1.46 +/- 4.21 degrees, respectively. Several techniques for pedicle screw insertion such as computer-assisted navigation, CT-based navigation, and acquisition of fluoroscopic intraoperative pedicle axis views have been used for improving accuracy. However, there remains a possibility of misplacement, and these costly procedures often require delivery of a high x-ray dose to both patients and surgeons, and/or time-consuming configuration of reference points during surgery. The CT cutout technique is an easy, low-cost procedure that can be performed with the aid of single-plane fluoroscopy and without the need of configuration. This new technique shows great promise for safe pedicle screw insertion for the cervical spine.