Design and Implementation of a Snake Robot for Cranial Surgery

Craniosynostosis involves premature fusion of the cranial sutures resulting in abnormal skull morphology and elevated intracranial pressure. Surgical intervention is necessary to correct the skull shape and to allow for unrestricted brain growth. This study presents a novel snake robot designed for minimally invasive cranial osteotomies featuring two articulating bending segments. The end-effector comprises a bone-punch for bone-cutting, a dural and scalp retractor, as well as channels for an endoscope and an instrument. The robot's bending mechanism is driven by tendons and utilizes geared linkages to facilitate a smooth curved shape. Pre-tensioned antagonistic tendons allow the robot to modulate its stiffness to adapt to external loads. A follow-the-leader algorithm was implemented to guide the robot along a skull cutting path. Experimental results demonstrated that at maximum bending of $60^{\circ}$ for segment 1 and $90^{\circ}$ for segment 2 there was a $15.9^{\circ}$ and $11.5^\circ$ error, respectively. Position errors ranged from 2.5 to 21.5 mm when tracing a curved path. The tool increased stiffness with tendon pre-tensioning from 20–100 N during bent configurations $q_{1}$ and $q_{2}$ for segments 1 and 2, respectively, at $[q_{1},q_{2}]=[0^{\mathrm{o}},30^{\mathrm{o}}]$ and $[30^{\circ},60^{\circ}]$. Tip deflection 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 each configuration, respectively. Ex vitro trials demonstrated the robots ability to perform simulated osteotomies on skull models to 68–73% of desired path lengths with a maximum deviation of 8 mm.