Background: The great accuracy of computer-assisted operative systems for pedicle screw insertion makes them highly desirable for spinal surgeries. However, computer-assisted pedicle screw placement is expensive, and the learning curve for these techniques is significant. We have developed a novel method of spinal pedicle stereotaxy by reverse engineering (RE) and rapid prototyping (RP) and have validated the method's accuracy by cadaveric and clinical study.
Methods: A volumetric CT scan was performed on each desired lumbar vertebra and a three-dimensional (3D) reconstruction model was generated with MIMICS 10.1, while the optimal screw size and orientation were determined using UG Imageware 12.1. A drill template was created using UG Imageware 12.1, with a surface that is the inverse of the vertebral surface. The drill template and its corresponding vertebra were manufactured using RP. The method was tested on six cadavers without any fluoroscopic control at surgery. Eventually, the technology was applied in six clinical cases.
Results: The accuracy of the drill template was confirmed by preoperatively drilling the screw trajectory into the vertebra biomodel. In the cadaveric experiment, 36 pedicle screws were inserted and no pedicle perforation was observed by postoperative CT scan. In the six clinical patients, the best fit for positioning the template was easily found manually during the operation. The required time between fixation of the template to the lamina and insertion of the pedicle screw into each segment (one or two vertebrae) was 1-2 min. In total, 22 screws were inserted into T12-L5, with two to four screws/patient. No misplacement occurred using the individual templates. Fluoroscopy was used only once after all the pedicle screws had been inserted. The method significantly reduces operation time and radiation exposure for the members of the surgical team.
Conclusions: The authors have developed a novel computer-assisted drill template for lumbar pedicle screw placement. This method has shown its ability to customize the placement and size of each screw, based on the unique morphology of the lumbar vertebra. The potential use of drill templates to place lumbar pedicle screws is promising.