Bone-mounted miniature robotic guidance for pedicle screw and translaminar facet screw placement: part 2--Evaluation of system accuracy.

Objective: To evaluate the accuracy of a novel bone-mounted miniature robotic system for percutaneous placement of pedicle and translaminar facet screws.

Methods: Thirty-five spinal levels in 10 cadavers were instrumented. Each cadaver's entire torso was scanned before the procedure. Surgeons planned optimal entry points and trajectories for screws on reconstructed three-dimensional virtual x-rays of each vertebra. Either a clamp or a minimally invasive external frame was attached to the bony anatomy. Anteroposterior and lateral fluoroscopic images using targeting devices were obtained and automatically registered with the virtual x-rays of each vertebra generated from the computed tomographic scan obtained before the procedure. A miniature robot was mounted onto the clamp and external frame and the system controlled the robot's motions to align the cannulated drill guide along the planned trajectory. A drill bit was introduced through the cannulated guide and a hole was drilled through the cortex. Then, K-wires were introduced and advanced through the same cannulated guide and left inside the cadaver. The cadavers were scanned with computed tomography after the procedure and the system's accuracy was evaluated in three planes, comparing K-wire positions with the preoperative plan. A total of fifty-five procedures were evaluated.

Results: Twenty-nine of 32 K-wires and all four screws were placed with less than 1.5 mm of deviation; average deviation was 0.87 +/- 0.63 mm (range, 0-1.7 mm) from the preoperative plan in this group. Sixteen of 19 K-wires were placed with less than 1.5 mm of deviation. There was one broken and one bent K-wire. Another K-wire was misplaced because of collision with the previously placed wire on the contralateral side of the same vertebra because of a mistake in planning, resulting in a 6.5-mm deviation. When this case was excluded, average deviation was 0.82 +/- 0.65 mm (range, 0-1.5 mm).

Conclusion: These results verify the system's accuracy and support its use for minimally invasive spine surgery in selected patients.