Surgical Bone Drill System With Piezoelectric Vibration Sensor-based Distal Cortical Bone Breakthrough Detection and Automatic Stop Function

Bone drilling is a procedure routinely performed in orthopedic surgery to create screw insertion paths. When the drill bit breaks through the distal cortical bone, over-drilling may occur due to residual axial force and rotational or feed inertia, potentially damaging surrounding soft tissues, blood vessels, nerves, and adjacent anatomical structures. This paper proposes an attachable piezoelectric sensor-based vibration signal processing method for real-time detection of distal cortical bone breakthrough while requiring minimal mechanical modifications to existing surgical drill devices. The piezoelectric vibration sensor is a passive element that can be attached to the outer surface of the drill sleeve without further hardware modifications. Therefore, it offers advantages in terms of low sensor cost and easy applicability to existing drill systems. In the proposed method, the vibration signal measured by the piezoelectric sensor is analyzed using a DQ-transformation-based synchronous detection method to identify the timing of distal cortical bone breakthrough. The detected breakthrough signal is then used to automatically stop the drill, thereby helping to limit over-drilling. By applying the DQ transformation, the target frequency component is converted into a DC component in the rotating reference frame, enabling the component to be extracted using only a low-pass filter with a fixed cutoff frequency. Therefore, even when the driving frequency of the drill rotation motor changes, consistent detection characteristics can be obtained without redesigning the filter. In addition, the detection threshold for breakthrough judgment is determined using the signal acquired during drilling of the proximal cortical bone and then applied to the distal cortical bone drilling section. This allows the proposed method to adapt to variations in vibration signal magnitude caused by differences in bone properties and drilling conditions. Based on the proposed method, a program was implemented to detect distal cortical bone breakthrough in real time and automatically stop drill rotation and axial feed. Repeated experiments using model bones confirmed that the proposed method can detect distal cortical bone breakthrough even under varying drill motor driving frequency conditions. In the automatic stop experiment, the mean protrusion length of the drill bit beyond the distal cortical bone was 1.01mm, and the maximum protrusion length was 1.3mm.