Design of a Stiff Steerable Grasper for Sinus Surgery1

摘要

With the advent of endoscopic sinus surgery in the late 1980's [1], a completely new surgical field was born. The endoscope, passed through the natural orifice of the nose, allowed for much more precise visualization of the operative field and enabled a new understanding of the function of the sinuses. Today, functional endoscopic sinus surgery (FESS) is commonly used to improve the sinuses' natural drainage pathways in patients with chronic sinusitis, to remove pathologies such as nasal polyps and tumors, and even to access the skull base to remove brain tumors.Commonly used angled endoscopes allow for visualization of nearly every portion of the sinus cavities and skull base. However, traditional tools have not enabled adequate surgical access to all of these areas. This is because the current surgical method requires a nearly direct line of access from the opening of the nose to the surgical target. Due to anatomical obstacles, not all areas visible to the endoscope can be directly accessed in this way. As a result, procedures have been developed to remove anatomical structures in order to clear a direct line of access to hard-to-reach targets. However, removal of these structures comes at a cost, with complications including vascular, nerve and soft tissue damage that can result in pain or numbness in the mouth and face.Current technique requires one hand to hold the surgical instrument, while the other hand is typically occupied holding the endoscope, as shown in Fig. 1. Generally, these tools are supported entirely by the surgeon's hands, in contrast with other types of laparoscopic surgery in which a trocar provides additional support. As a result, tools must be lightweight and comfortable to hold. These tools have traditionally been designed to be rigid (so as to be easily controlled with one hand), though not necessarily straight. In an attempt to reach around corners and avoid obstacles in the anatomy, some devices incorporate curved tool shafts. However, these are limited in their maneuverability, since the curved shape is fixed during surgery. These rigid tools have been adequate for the majority of surgeries, but as techniques have advanced, surgeons have reached the limits of what they can accomplish with these tools. In order to avoid the need to remove tissue in order to access hard-to-reach sites, new tools must be developed which are capable of navigating through angled pathways in the nasal cavities. A new approach to this problem involving a stiff yet elastic steerable tool tip is presented in this paper. This approach uses a continuum structure. For a review of prior uses of continuum structures in robotic tools, see Ref. [2].Our objective was to develop a stiff, yet bendable manual grasper with controllable curvature, allowing the surgeon to easily steer the tip of the tool within the sinuses. The device was required to be relatively stiff to effectively accomplish surgical tasks such as grasping and cutting; yet we also required the tool shaft to have the ability to bend locally near tool tip. The goal was to access a larger set of potential targets in the sinus cavities, without the need for a clear line of access between the opening of the nostril and the target site.User control represented an additional design challenge. We sought a design in which a single hand could comfortably and intuitively control gross tool manipulation, bending of the tool shaft, and gripper opening and closing. We targeted a shaft diameter of 4 mm or less, such that the device could fit through a nostril, and a shaft length and handle width comparable to those of currently available sinus surgery tools (approximately 80 mm and 5 mm, respectively). The CAD model and physical prototype we developed are shown in Fig. 2.To allow for tool shaft bending, we implemented a “multibackbone” continuum mechanism [3] at the distal end of the shaft, shown in detail in Fig. 3. It consists of a set of 4 superelastic nitinol wires passed thr