Automated Polyaxial Screw Placement Using a Commercial-Robot-Based, Image-Guided Spine Surgery System

Robotic spine surgery systems, used for placing pedicle screws, have been in clinical use since 2004; however, these systems act only as a positioner for guide tubes, which the surgeon uses to manually advance tools to prepare the site and place hardware (e.g., pedicle screws). This article presents the development, operation, and evaluation of a new, commercial-robot-based, image-guided surgery system that automates the process of bone preparation and polyaxial screw placement. The system is based on the KUKA LBR iiwa 7-axis collaborative robot. Fiducial marker and screw locations are defined on a pre-operative CT image using the 3D Slicer open source image visualization platform. The system uses the robot's internal localization system for registration, by touching fiducial markers in a hand-guiding mode. A rotary-motor end effector with exchangeable tools is used for both hole-drilling and screw placement. A novel single-motor based mechanism was developed for placing polyaxial pedicle screws. An accuracy test was performed by placing polyaxial screws in synthetic vertebrae which mimic the mechanical properties of human bone. In placing 10 screws, the entry point accuracy was 0.49 ± 0.17 mm and the destination point accuracy was 1.49 ± 0.46 mm. The results compare favorably to evaluations of commercial robotic spine surgery systems.