56. Development and Characterization of a Cranial Bone Cutting Snake Robot for Craniosynostosis Surgery

PURPOSE: There is an evolution towards more minimally invasive approaches for the treatment of patients with craniosynostosis. Minimally invasive approaches utilize rigid, straight instruments, which limits the extent of the osteotomies possible along the curvature of the skull using minimal access incisions. The ability to perform more extensive osteotomies using minimal access incisions may provide more patients with craniosynostosis the option and benefits of minimally invasive surgery. The following study involves the development and characterization of a novel, minimally invasive robotic bone cutting tool for craniosynostosis surgery that allows for extensive osteotomies through a minimal access incision. METHODS: A novel snake robot was developed for navigation along the cranium that was coupled to a 7-degree-of-freedom industrial manipulator for controlling its position and orientation. The snake robot comprises an end-effector, a bending section with two segments, and an actuation unit. The end-effector incorporates a bone punch, a dural and scalp retractor, as well as channels for an endoscope and surgical instruments. The bending mechanism utilizes a geared linkage design which allows for the segments to articulate in a smooth constant curvature shape. The bending actuation is controlled via pre-tensioned antagonistic cables that allow the robot to modulate its stiffness under external loads. A follow-the-leader algorithm was implemented to guide the robot along skull-cutting paths. Three experiments were performed: (1) a kinematics accuracy test validating the mapping between cable length and bending configuration, (2) a stiffness characteristics by applying an external load to measure tip deflection under varying bending configurations and (3) an ex-vitro trial to demonstrate the manipulator’s reachability along three-dimensionally (3D) printed craniosynostosis skull models. RESULTS: Accuracy testing demonstrated bending errors of 15.9° and 11.5° for the two segments at maximum bending angles of 60° and 90°, respectively, with position errors ranging from 2.5 to 21.5 mm during path tracing. The stiffness of the tool increased with tendon pre-tensioning from 20-100 N during bent configurations for both segments at specific bending angles. Tip deflection was reduced from 0.42 to 0.03 cm and 0.37 to 0.10 cm during axial loading, and from 11.40 to 3.88 cm and 3.62 to 0.48 cm during radial loading for different configurations. Ex-vitro trials demonstrated the robot’s ability to perform simulated osteotomies on craniosynostosis skull models, achieving 68-73% of desired path lengths with a maximum deviation of 8 mm. CONCLUSION: This study presents a novel steerable snake robot with adjustable stiffness, capable of following predefined paths and performing osteotomies on simulated skull models. The results demonstrate that the proposed system holds significant potential as a promising new approach to cranial surgery.