Using a Force-Controlled Robot for Probing-Based Registration and Automated Bone Drilling in Pedicle Screw Placement Procedures

Pedicle screw placement is a crucial phase in various spine surgical procedures. In the recent years, robotic solutions have been proposed to assist it. They require intra-operative registration based on CT or fluoroscopic imaging, raising risks for patients and surgeons. In this study, we investigated registration methods that remove the need for intraoperative imaging. They involve a robot holding a mechanical probe whose tip contacts the bone at sparse locations. This involves either surgeon's manual guidance, or automatic force-control based probing. Further, once the anatomy is registered, we automate the entire process, including the pedicle preparation and drilling, with the same force controlled robot. Ten drillings were performed in five lumbar vertebrae of a porcine sample using a custom-designed instrument mounted on the robot's end-effector. Preoprative and postoperative scans were performed to evaluate the registrations and drillings quantitatively. The mean difference between the planned and postop-measured drilling orientations was $2.2^{\circ} ({\text{Max}}.\ 4.4^{\circ})$. The mean distance between the planned entry points and the postop-measured drilling paths was $2.2 mm (\text{Max}. \ 4.1 mm)$. These results open perspectives for X-ray free robotic operations and pedicle screw placement automation.