Percutaneous Placement of Pedicle Screws in the Lumbar Spine Using a Bone Mounted Miniature Robotic System First Experiences and Accuracy of Screw Placement

Study Design. A prospective analysis. Objective. The idea of this study was to evaluate a new miniature robotic system providing passive guidance for pedicle screw placement at the lumbar spine. Special focus was laid on the postoperative accuracy of screw placement. Summary and Background Data. Recent technical developments lead to a minimization of pedicle screw fixation techniques. However, the use of navigational techniques is still under controversy. Methods. Patients selected for a minimal invasive posterior lumbar interbody fusion received a spiral computer tomographic scan before surgery. The miniature hexapod robot was mounted to the spinous process and the system moves to the exact entry point according to the trajectory of the surgeon's preoperative plan. After minimal invasive screw placement all patients received routinely a postoperative spiral computer tomographic scan. Screws placed exactly within the pedicle were evaluated as group A, screws deviating < 2 mm were evaluated as group B, >= 2 mm to < 4 mm(group C); >= 4 mm to < 6 mm(group D); and more than 6 mm (group E). Results. Thirty-one patients received a PLIF with percutaneous posterior pedicle screw insertion using the bone mounted miniature robotic device. A total of 133 pedicle screws were placed. The majority of the screws were placed in L5 (58 screws; 43.6%). In axial plane, 91.7% of the screws were evaluated as group A and 6.8% were evaluated as group B. In longitudinal plane, 81.2% of the screws were evaluated as group A and 9.8% were evaluated as group B. In 1 screw (L5 right) the postoperative evaluation was done as group C (axial plane) and D (longitudinal plane). In 29/31 cases the integration of the miniature robotic system was successful. Conclusion. In our study the first clinical assessment of a new bone mounted robot system guiding percutaneous pedicle screw placement was done. A deviation < 2 mm to the surgeon's plan in 91.0% to 98.5% verifies the system's accuracy.