Study, realization and validation of an active scope-holder for laparoscopic surgery - EVOLAP

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Written by Benoît Herman

Contact: Benoît Herman

 

Abstract

Thirty years ago, the emergence of endoscopic technology opened up the way to minimal access surgery. This new approach strongly decreases the size of incisions and scars, reducing per- and post-operative traumatism and risk of infection.

Advantages in terms of pain and esthetics played a large part in the quick expansion of laparoscopy in urology, gynecology and digestive surgery.

But whereas this technique offers many advantages to the patient, it complicates surgical gestures. In particular, manual manipulation of the laparoscope poses many ergonomics problems. Our goal is to design a robotic scope-holder that allows the surgeon to teleoperate the laparoscope.

 

Starting from this initial demand, this thesis sets out to study laparoscopic surgery into detail, in collaboration with practitioners. Through the clarification of problems that they encounter, performance specifications are established.

Subsequently, main choices of the robot's structure are layed down. Design of device's subsets follows a rational process until realization of a functional prototype. Particular attention is paid to general ergonomics of the system and its control interface.

An experimental clinical trial ends this work and validates the principle of solution. We finally propose a few design improvements and a series of possible complementary studies and trials, and go back over objectives identified initially, in the light of results achieved and experience acquired in the course of this research.

Background

Robots have several capabilities which surpass human performances. Their motions are precise and repeatable, they can adapt their trajectory by measuring forces exerted or by analyzing images, they never get tired nor tremble, they do not fear nuclear radiations...

Most of these facultiies are advantageous in medicine, and in particular in surgery. Therefore, at the end of the eighties, the idea formed of introducing robots in operating rooms, by adapting existing devices to fulfill constraints related to this particular environment.

Unfortunately, although the first clinical results demonstrate the "superiority" of those machines over human hand for specific tasks, industrial manipulators are not designed for surgery. Many safety issues arise about nearness of human beings, regarding speeds and forces produced. Moreover, usual robots are heavy and bulky, though space around the operation table is highly restricted. Finally, they work most of the time autonomously, and can therefore only replace the surgeon, and can not assist him. For these three reasons, robots, although endowed with undeniable qualities, are still struggling for finding their place in hospitals.

To reverse the trend, an alternative approcah seems more promising: one must transform the robot in an ergonomic and performant instrument capable of interacting with the surgeon, so as to extend abilities of the latter for a specific application without replacing him. To take up the challenge, and contribute to the improvement of healthcare quality by developing devices that are efficient, ergonomic and economically viable, it is essential to collaborate throughout research with surgeons, who know the demand and can tell what will be accepted or not by their peers, and with manufacturers of medical devices, familiar with the economic and normative sides.

From this perspective, the CEREM launched the research project EVOLAP, aiming at designing a robot for assistance to laparoscopic surgery, in collaboration with the Gynecology Unit (GYNE) of UCL and the Laboratoire d'Informatique, de Robotique et de Microélectronique de Montpellier (LIRMM) of Université Montpellier 2.

Laparoscopic surgery

Thirty years ago, the emergence of the endoscopic technology opened up the way to minimal access surgery. This new approach strongly decreases the size of incisions and scars, reducing per- and post-operative traumatism and risk of infection. Advantages in terms of pain and esthetics played a large part in the quick expansion of laparoscopy in urology, gynecology and digestive surgery.

But whereas this technique offers many advantages to the patient, it complicates surgical gestures. In particular, manual manipulation of the laparoscope poses many ergonomics problems:

lack of coordination between the surgeon and the camera, usually carried by an assistant, reducing depth perception and disrupting hand-eye coordination;

image instability due to hand tremor, complicating displacements towards a specific target and rapidly inducing visual fatigue;

need for a supplementary hand, making solo surgery impossible even for straightforward cases.

Method

By a review of scientific litterature and several discussions with practitioners, notably at the European Institute for Tele-Sugery (EITS), we rapidly highlighted the importance of camera manipulation on the surgical procedure and the advantage of entrusting this task to a robotized device. We then defined the design objectives by means of the objectives tree method. A set of requirements was derived from this base with clinical and industrial partners.

Subsequently, fundamental choices of the robot structure and its control interface were laid down during the conceptual design of the draft of solution. As far as possible, we tried to objectify our choices between foreseen possibilities by comparing them through criteria from the objectives tree. Particular attention was paid to the general ergonomics of the device throughout the design of the various subparts that make it up.

The solution was then implemented in an active functional prototype. In a collaboration between doctors and engineers, materialization holds a major importance. It helps the exchange of ideas and informations on the formers' needs and on the capabilities that the latters have to answer at best.

 

 

In order to complete this long design stage successfully, we were forced to carry out several specific studies intended to dimension some parts, to caracterize performances, or to confirm the pertinence of some former choices. The modeling of the robot by a multybody approach constituted the base of the dimensioning of actuators and of the characterization of the robot's back-drivability. It also allowed to analyze in detail the influence of the selection of the operational frame on the intra-abdominal image displacements. Several testings enabled to check regulartly the pertinence of the solution and its embodiment, to improve the installation procedure of the robot at the beginning of the surgery, and also to adjust the control interface.

An experimental clinical trial concluded this work and enabled to reveal some avenues of improvement of the design so as to increase the robot's performances. Above all, it validated the principle of solution that we devised, which seems to meet the surgeons' expectations expressed in the early stages of the project.

 

Our solution

The EVOLAP robot that we developed during this doctoral research project is made of the following main subparts:

a remote main manipulator, which generates lateral displacements of the endoscopic image by moving a point of the laparoscope on the surface of a sphere centered on the incision;

a local manipulator, that modifies the image magnification by translating the laparoscope into the trocar without any motion of the main manipulator;

and connecting elements, namely a passive articulated arm that links both manipulators via two passive terminal revolute joints, and a fixation to the lateral rail of the table that allows the height adjustment of the robot.

It has thus a decoupled architecture with passive-RCM that can move the distal extremity of the laparoscope in a large workspace inside peritoneal cavity, without requiring large robot motions above the patient's abdomen.

The main manipulator has an original kinematic structure composed of orthogona parallelograms that restricts any rotation of its end-effector and translates the latter on the surface of a sphere. This motion can be reproduced remotely above the patient's abdomen by the grasping point of the laparoscope via the articulated arm, without need for any alignment between the device and the incision. The imposition of the position of this grasping point with respect to the incision will then induce passively the laparoscope angular motions, thanks to the presence of buth free pivots of the RCM. One can thus give priority to the optimal placement of the surgical team members around the table, the root being positionerd afterwards in a convenient place without bothering them.

 

 

A Miniature joystick mounted on one of his instruments enables the surgeon to control the robot motions. This interface is simple, reliable, and responds immediately to orders. It also ensures omnidirectional displacements of the image to reach the target in straight line, which is much more natural than to proceed by successive horizontal and vertical steps. Speed can be adjusted in real time in function of the tilt angle of the joystick, so as to perform fast motions in wide view and precise adjustments in close-up.

Finally, although this manipulator is active, it was designed and sized to allow the surgeon to grasp the laparoscope directly at some moments for moving it by hand without having to disconect it from the robot. This functionality is useful in various situations like the installation and removal of the device, or during a general exploration of the abdominal cavity, that requires wide and quick motions, and helps the surgeon to find landmarks by moving the camera by himself. Transmissions were designed to answer this requirement and a balancing mechanism with spring was integrated to make manual manipulation easier, reduce required torques in normal working, and minimize the risk of fall of the robot mobile parts in case of power loss.

 

Contributions

Scientific and technological contributions of this work can be summarized in three points:

an analysis of the needs of laparoscopic surgery, based on an identification of the problems related to the manual manipulation of the laparoscope and on a review of existing scope-holders;

a rational and systematic study of an ergonomic and innovative mechatronic structure aiming at filfilling these needs, being protected by an international PCT application (available here);

an optimization of the control of the proposed device, based on the modeling of camera kinematics that enabled to determine the intra-abdominal image displacements in function of the chosen operational frame and the consequences on the surgery process.

The main results gathered at the end of this thesis are firstly, the design and realization of a passive prototype (without actuators) to demonstrate the principle and of an active prototype of the main manipulator of EVOLAP, and a discussion about the technological choices we made (publication in IJMRCAS); and secondly, the experimental validation of the global principle of solution, during a gynecologic surgical procedure in real conditions performed with the active prototype (publication in JMIG).

Collaborations

GYNE - Service de gynécologie et andrologie, Cliniques universitaires Saint-Luc, Louvain-en-Woluwe, BELGIQUE

LIRMM - Laboratoire d’Informatique, de Robotique et de Microélectronique de Montpellier, Montpellier, FRANCE

IRCAD - Institut de Recherche contre les Cancers de l’Appareil Digestif, Strasbourg, FRANCE

 

Financial resources: FIRST Europe Objectif 3 “EVOLAP” n° EPH 3310300R060F/415850 Région Wallonne – Fonds social européen