Computer-Assisted Pedicle Screw Insertion

Summary Pedicle screw insertion is used for treatment of various disorders such as fractures, scoliosis, spondylolisthesis, or degenerative instabilities. With conventional procedures, there are between 10% and 40% of misplaced pedicle screws. Between 1998 and 2002, 2 navigation systems were used at the University Hospital of Grenoble (CHUG), France, for pedicle screw placement: a computed tomography (CT)-based and a fluoroscopy-based navigation system. Ninety-one patients were operated on with either systems, and 235 pedicle screws were inserted between T4 and L5 in 43 scoliosis and 48 fractures, spondylolisthesis, or degenerative instabilities. With the CT-based navigation system, 6.2% of the pedicle screws were misplaced (cortex penetration superior or equal to 2 mm). With the fluoroscopy-based navigation system, 14% of the pedicle screws were misplaced. The advantages of using a CT-based navigation system are there is no intraoperative x-ray radiation and you get real 3-D navigation views; the drawbacks are a preoperative CT scan is necessary and it requires time-consuming registration (2–10 min). The advantages of using a fluoroscopy-based navigation system are there is no preoperative imaging required, there is less radiation for both the patient and staff (as compared with conventional fluoroscopy), and no intraoperative registration is required (images are calibrated directly in patient reference system). The drawbacks are there is variable image quality and, most important for scoliosis cases, there are no real 3-D navigation views. Regarding the basic principle of computer-assisted surgery (CAS) systems, ie, multimodal data registration, some new technologies that are currently under development or testing are presented. The authors believe they will soon replace the existing data registration techniques (currently based on manual data collection directly on patient bone surface) in the next generation of CAS systems, mainly because of their increased accuracy and efficiency, but also because of easier implementation in the operating room. All of these new technologies should allow percutaneous pedicle screw placement or other type of spine surgery procedure (minimally invasive surgery) to be performed in the very near future.