All-Ultrasound-Guided Path Planning for Robotic Pedicle Screw Placement

Pedicle screw placement (PSP) is a challenging procedure in spine surgery, due to poor visualization of the vertebrae and blood vessels. This has led to the development of navigation systems that improve safety and clinical outcomes. Navigation further enabled minimal invasive approaches for PSP. Current navigation systems require a preoperative computed tomography (CT) scan, followed by manual planning by the surgeon to decide screw trajectories. Intraoperative fluoroscopy imaging may be employed to register the preoperative plan with the patient's anatomy frame or even design screw trajectory planning in real-time for each pedicle individually. This is a rather lengthy procedure that involves harmful radiation to which the surgeon is exposed repeatedly. This article explores a novel approach for PSP guidance that replaces manual planning while solely relying on 3D ultrasound (US) reconstruction, hence reducing the need for radiation. Based on an intraoperative US reconstruction, a set of anatomical landmarks of the spine are identified. Subsequently, a coordinate frame is computed per vertebra. The screw path is then generated automatically using the learned relations between the landmarks and optimal screw paths. A five-fold cross-validation is conducted on the posterior surface of CT spine data involving 90 PSP paths. The algorithm is then tested on another 50 PSP paths of the 3D-printed spine phantoms corresponding to human spine CT data. Results show that for 4 mm and 6 mm diameter screws, 98% and 84% of the computed trajectories are within the required surgical precision, respectively. Using the US-based path planning led to -0.34 ± 3.66 ° and -0.45 ± 4.32 ° orientation errors in the sagittal and axial planes, respectively.