Development of an Innovative Active Flexible Instrument for ENT Surgery
Minimally Invasive Surgery (MIS) is a modern surgical technique where surgeons operate through small incisions, called keyholes, rather than making large cuts to access the patient's organs. MIS is known to reduce patient trauma and shortens recovery time. To reach even lower levels of invasiveness, Natural Orifice Transluminal Endoscopic Surgery (NOTES) has been developed. In NOTES, specific sites are accessed by inserting instruments through natural orifices. While this procedure allows to limit the incisions to access the pathology, it also highly constrains the surgical workspace due to the geometric complexity of the human anatomy. Endoscopic maxillary sinus surgery is an example of such constrained workspace surgery. In endoscopic maxillary sinus surgery, the maxillary sinus is accessed through the nasal cavity which constitutes a narrow and tortuous pathway. Surgeons, however, still use rigid and straight or pre-bent instruments for this procedure which forces them to resect healthy tissues to access the pathology inside the maxillary sinus.
This doctoral work aims at enhancing constrained workspace surgery by proposing new design and control strategies for flexible, steerable instruments. A further objective is to enable single-handed operation of these instruments. This allows the surgeon to be in full control of the operation while being able to use another instrument with his/her other hand.
Finally, as the geometry of the natural orifice (i.e. the nasal cavity) varies to great extent for each patient and since developing patient-specific instruments would not be economical, a technique is developed to ensure coverage of a large share of the population. The resulting instrument provides the surgeon with an innovative miniature, intuitive, flexible instrument with enhanced dexterity while reducing the need to resect healthy tissues. The different research contributions at the origin of this work can be summarized in four points.
First, a structured statistical shape model-based method was created from a series of patient's medical images of the targeted anatomy in order to derive the instrument specifications for a specific procedure. The proposed method is generic but was applied in this doctoral work to the maxillary sinus and the nasal cavity. It allowed to extract essential design-oriented data for the development of flexible instruments for endoscopic maxillary sinus surgery.
Second, active add-ons intended to be coupled to commercial passive flexible endoscopes were designed. Those add-ons allow to improve the operation and control of otherwise passive commercial endoscopes. They also allow to speed up the development cycle of active flexible instruments. In this work, they have been used to evaluate the feasibility of single-handed flexible, steerable endoscopes for fetal surgery. They showed a good potential to ease surgical procedures by using flexible instruments.
Third, an important step was made to further miniaturize McKibben-actuated surgical instruments. To do so, a novel miniature pneumatic actuator with integrated channel, called "concentric muscle", has been designed and tested for integration in miniature flexible instruments. Moreover, open loop control methods were developed in order to provide accurate position control. This approach allows to avoid integration of distal position sensors and hence keep the instrument compact. More specifically, a hysteresis compensation algorithm was developed and tested to control the bending of a flexible fetoscope in open loop. The algorithm could successfully compensate for the pneumatic actuator hysteresis and friction in the instrument. A compact capacitance sensor was also designed for miniature artificial muscle actuators. The sensor predicts the muscle length with a 0.31mm precision over 80\% of the muscle's total contraction range. Lastly, a large displacement model was introduced. The model predicts the bending angle of a flexible Nitinol side-notched backbone with an accuracy of as low as $5.4^\circ$ ($3.1 \%$). Those backbones are often use as a flexible distal tip in flexible surgical instruments.
Fourth, a functional single-handed, steerable endoscope for flexible endoscopic maxillary sinus surgery has been designed and built using the previously mentioned contributions. This endoscope is the thinnest active flexible endoscope ever reported for maxillary sinus surgery, as far as the author is aware of. It was tested by two surgeons on a cadaver and showed an increased field of view in comparison to currently used instruments, which allowed limiting healthy tissue resection.
This doctoral work provides tracks to enhance the miniaturization, flexibility and control of flexible instruments for constrained workspace surgery. Future directions are proposed to further enhance the here developed technology and make it available in the operating room. Such directions could consist in increasing the performance of the proposed actuators, sensors and control techniques, as well as investigating other types of instruments than flexible endoscopes, e.g. flexible graspers that require extra rigidity when grasping.