Using Electrical Conductivity for Breach Prevention During Automatic Bone Drilling


Introduction. Dynamic Surgical Guidance (DSG) technology has proven to increase screw placement accuracy and prevent pedicle breaches based on the electrical conductivity measurement ability. The DSG technology provides a digital feedback signal represents tissue conductivity at the tip of the drilling device, indicating changes in the physiology encountered all along the drilling. Other state of the art surgical guidance are the popular navigated instrument and robotic arms, which however lack local and in situ feedback. Aims/objectives. To evaluate the ability of the DSG technology to automatically identify a near breach situation and to stop a drilling instrument mounted onto a robotic arm before a bone breach occurs, therefore, improving safety during screw placement when combined with robotics. Methods. 104 Lamb vertebrae were used to provide physical characteristics close to human bone yet allowing large population sample size. The specimens were immersed in saline to replicate conductivity found in the body fluids and tissues surrounding the bone in-vivo. The drilling instrument was mounted onto a drill on a robot arm. The system was defined to detect a conductivity increase representative of a near breach condition and automatically stop the robotic drilling if such event is detected. Entry point and drilling trajectory were manually defined for each specimen, targeting on purpose the spinal canal. Once the drilling sequence was launched, the drill rotation and feed rate along the defined trajectory were maintained by the robot until a stop command was triggered by the DSG signal monitoring algorithm. The acceptance criteria were that upon stopping, the instrument position must be positioned +/-2mm from the border between the bone and the canal (either grade A but in a near breach position, or grade B maximum). Results. 104 vertebrae were drilled, and the robot automatically stopped in 104 cases (100%). No spinal canal infringements were detected by the camera, and after instrument removal, manual palpation using a ball tip feeler confirmed the absence of breach in all 104 drillings (0% false negative). Post experiments CT scans analysis confirmed that all drillings stopped less than 2mm from the canal (0% false positive). Conclusion. Use of DSG in an automated robotic control loop allowed 100% breach prevention. These results demonstrate that DSG sensing when integrated at the tip of a drill or an implant could bring additional safety and autonomy in surgical robotics by providing additional accurate information regarding the device position within the bone.

Annual Forum ‘21 – Society for Minimally Invasive Spine Surgery (SMISS)