Development of a New Technique for Pedicle Screw and Magerl Screw Insertion Using a 3-Dimensional Image Guide

Study Design. We developed a new technique for cervical pedicle screw and Magerl screw insertion using a 3-dimensional image guide. Objective. In posterior cervical spinal fusion surgery, instrumentation with screws is virtually routine. However, malpositioning of screws is not rare. To avoid complications during cervical pedicle screw and Magerl screw insertion, the authors developed a new technique which is a mold shaped to fit the lamina. Summary of Background Data. Cervical pedicle screw fixation and Magerl screw fixation provide good correction of cervical alignment, rigid fixation, and a high fusion rate. However, malpositioning of screws is not a rare occurrence, and thus the insertion of screws has a potential risk of neurovascular injury. It is necessary to determine a safe insertion procedure for these screws. Methods. Preoperative computed tomographic (CT) scans of 1-mm slice thickness were obtained of the whole surgical area. The CT data were imported into a computer navigation system. We developed a 3-dimensional full-scale model of the patient's spine using a rapid prototyping technique from the CT data. Molds of the left and right sides at each vertebra were also constructed. One hole (2.0 mm in diameter and 2.0 cm in length) was made in each mold for the insertion of a screw guide. We performed a simulated surgery using the bone model and the mold before operation in all patients. The mold was firmly attached to the surface of the lamina and the guide wire was inserted using the intraoperative image of lateral vertebra. The proper insertion point, direction, and length of the guide were also confirmed both with the model bone and the image intensifier in the operative field. Then, drilling using a cannulated drill and tapping using a cannulated tapping device were carried out. Eleven consecutive patients who underwent posterior spinal fusion surgery using this technique since 2009 are included. The screw positions in the sagittal and axial planes were evaluated by postoperative CT scan to check for malpositioning. Results. The screw insertion was done in the same manner as the simulated surgery. With the aid of this guide the pedicle screws and Magerl screws could be easily inserted even at the level where the pedicle seemed to be very thin and sclerotic on the CT scan. Postoperative CT scan showed that there were no critical breaches of the screws. Conclusion. This method employing the device using a 3-dimensional image guide seems to be easy and safe to use. The technique may improve the safety of pedicle screw and Magerl screw insertion even in difficult cases with narrow sclerotic pedicles.