Mechanical Snakes: Path-Following Instruments for Minimally Invasive Surgery

Surgical procedures are inherently invasive as they require the surgeon to cut into the body to create a surgical pathway towards the diseased area, resulting in surgical trauma for the patient. The field of Minimally Invasive Surgery (MIS) strives to reduce surgical trauma by minimizing the size and number of incisions. The used instrumentation plays an important role in this pursuit. Instrumentation that is currently in use is either straight and rigid, demanding a straight surgical pathway, or flexible, allowing for multi-curved surgical pathways. The currently existing flexible instruments, such as, for example, a catheter guided by the blood vessel wall, rely on external support and guidance from the anatomical environment. The ability to follow multi-curved surgical pathways without the need for anatomical guidance extends the reach of surgery and is especially useful in less accessible areas such as, for example, the human skull base. The skull base is a dense anatomical area that, next to important structures such as the pituitary gland, supports a network of fragile nerves and blood vessels. In such a delicate anatomical environment, flexible instruments cannot find the necessary external support and guidance. This implies a need for instrumentation that is not only flexible, but also steerable. A logical next step is the development of steerable snake-like instruments that can follow multi-curved pathways through the body without the need for external support or guidance from the anatomical environment. This kind of functionality is new in surgery and a topic of research in multiple research institutes around the world. Nevertheless, solutions that are thin, stiff and affordable are not yet available. Similar to a biological snake that continuously adapts the shape of its entire body as it moves forward, the shape of a snake-like instrument also needs to be fully controllable. In practice, this will require multiple elements of the instrument to be controlled simultaneously. Humans are not particularly good in this kind of multi-tasking, while robots may excel at such tasks. Therefore, when trying to solve control problems concerning snake-like motion, a natural tendency exists to search for robotic solutions. Medical instrumentation does, for obvious reasons, have to meet high-quality standards. As a consequence, medical-grade robotics tend to be very expensive. The objective of this thesis is, therefore, to explore the possibilities for mechanically-controlled solutions for path-following cable-driven instruments that are suitable for surgical applications.