Design and Strength Analysis of Laparoscopical Tool for

Electrocoagulation Surgery

Martin Schmidt

, Marek Penhaker

, Jan Kubíček

, Jan Kráčmar

, Milada Hlaváčková

Petr Ihnát

and Petr Vávra

Department of Cybernetics and Biomedical Engineering, Faculty of Electrical Engineering and Computer Science,

VSB - Technical University of Ostrava, Czech Republic

Department of Mechanics, Faculty of Mechanical Engineering, VSB - Technical University of Ostrava, Czech Republic

Department of Surgery, University Hospital Ostrava, Czech Republic

Keywords: Laparoscopy, Hysteroscopy, Electrocoagulation.

Abstract: The goal of this paper was to design a new operating tool for hysteroscopy with better attributes than the

currently used tools. The purpose of creating this new tool is to shorten the time of surgery and enable the

surgeon to remove larger myomas and polyps. The designed tool may also be used as scissors and is

compatible with the currently used hysteroscopes. After the proposed instrument was created it was tested

and put through a strength analysis test.

1 INTRODUCTION

Hysteroscopy is an endoscopic examination method

that makes it possible to visually examine the uterine

cavity, extract a sample of the mucous membrane for

further histological examination and even perform

surgical treatment in the uterine cavity. The

hysteroscope is inserted through the vagina as shown

in Figure 1. (Citterbart, 2001)

The purpose of hysteroscopy is to examine the

uterine body (myometrium and endometrium) and

the cervix. Myometrium examination provides

information about the size of the uterus, its shape,

uterine malformations and uterine deformities

(submucosal lesions), which are defined by their

number, localization, consistency and angle of

deposition in the uterine wall. (Holub, 1999)

The endometrium is optically checked for its

maturation, distribution, vascularization and possible

inflammatory processes. (Citterbart, 2001)

The morphology of the cervix is evaluated, from

which it is possible to estimate its function and the

relationship of the cervix to the uterine cavity.

The uterine cavity may be seen as potential space

for optical diagnostics and surgical procedures,

although it is narrow, sloping and has a strong

myometrium that encloses it. The technical problems

of hysteroscopy, surgical hysteroscopy and

transcervical surgery are, in addition to the source of

light and suitable optics, given above all by adequate

and safe uterine cavity distention with appropriate

distension media for visual diagnostics and a

suitable type of instrumentation. (Holub, 1999)

Figure 1: Hysteroscope inserted into the uterus.

2 CURRENT STATE

For examinations and surgical procedures in uterine

cavity, panoramic hysteroscopes with 30° wide

angle telescopes are used. Less used are contact

hysteroscopes and microcolpohysteroscopes. (Holub

and Kužel, 2005)

Hysteroscopes can be categorized as:

Schmidt, M., Penhaker, M., Kubí

cek, J., Krá

cmar, J., Hlavá

cková, M., Ihnát, P. and Vávra, P.

Design and Strength Analysis of Laparoscopical Tool for Electrocoagulation Surgery.

DOI: 10.5220/0007578402690274

In Proceedings of the 12th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2019), pages 269-274

ISBN: 978-989-758-353-7

269

 Diagnostic - designed for minor transcervical

surgery

 Surgical - designed for more extensive

transcervical surgery (resectoscopes)

The panoramic hysteroscope is a modification of a

cystoscope. The hysteroscope diameters used are 3 -

4 mm, with a telescope diameter of 4 mm, with an

enclosing sheath of 5 or 5.5 mm in diameter. The

optical system may provide a direct or oblique

viewing angle. The hysteroscope is guided by

intense cold light from the extracorporeal source, the

hysteroscope's sheath is equipped with valves for

control of the inlet and outlet of the distension

medium. For therapeutic hysteroscopes (5.5 to 8 mm

wide sheaths), flexible or semirigid instruments with

a diameter of 5 or 7 Fr (French, with 1 Fr

corresponding to 0.33 mm) are introduced via a

special channel. The relatively limited transcervical

surgery instrumentation includes surgical probes,

palpators with various types of endings (sharp, blunt,

hook-shaped) cannulae, curettes, pliers and scissors.

For hysteroresectoscopes are recommended

telescopes with an angle of 12 ° and a diameter of 3

or 4 mm. (Holub and Kužel, 2005)

The hysteroscope instrument with a diameter of

8 or 9 mm (hysteroresectoscope) is supplemented

with a ball and a loop for ablation of the

endometrium. Instruments of the resectoscope are

semirigid. For surgical procedures in the uterine

cavity, it is recommended to use semirigid, less

flexible instrumentation. Flexible tools are not

considered suitable for intrauterine surgery. Flexible

hysteroscopes usually do not require dilatation of the

cervix for insertion and fixation of the cervix when

they are introduced. Their outer diameter is 3.5 - 3.7

mm, their flexibility enables the surgeon to operate

in angles up to 100 °. The viewing angle is direct,

the angle of view is 90 °, and the depth of the

observed field is between 1 and 50 mm. (Holub and

Kužel, 2005)

Hamou's microcolpohysteroscope allows

panoramic and constant observation with

magnification of 1 - 150 times (most frequently used

is observation without magnification or with

magnification 20 times). It has a diameter of 4 mm

and is introduced with a sheath of 5.2 mm diameter.

Because of its small diameter it is suitable for

hysteroscopic diagnostics and for its special

magnification possibilities it is also usable in

gynecological oncology. (Kužel, 1996)

In contact hysteroscopes, light reflects into the

uterine cavity, allowing intrauterine visualization

without uterine cavity expansion and with no light

source, except when photographs of the examined

tissue are required. Contact hysteroscopy is not

widely used because of difficult interpretation of

results and limitation of surgical options in the

absence of a panoramic view. (Holub and Kužel,

2005)

2.1 Currently Used Hysteroscopy Tool

For ambulatory hysteroscopy one of the most widely

used tools is a tool by Johnson & Johnson,

specifically from their GYNECARE Gynecological

Division, called Gynecare Versascope. The current

work was set to improve upon the design of this tool.

(Penhaker et al., 2004)

2.1.1 Gynecare Versascope

The hysteroscope is designed to examine the

cervical canal and uterine cavity for diagnostic or

therapeutic use. The Gynecare Versascope is used to

create and maintain the uterine distension and to

gain access to the uterine cavity for the

hysteroscope. This tool is shown in Figure 2.

Figure 2: Gynecare Versascope hysteroscope.

Characteristic features of the tool:

 Disposable case

 Dimensions are so small that the tool can be

inserted without distension into almost every

cervix

 Designed to minimize trauma and discomfort

 Slight curvature of 10 ° extends the field of

vision and operation

 The working channel is slightly enlarged after

insertion so that tools with a diameter of 2 mm

can be used

 The rotating part rotates at a 360 ° angle and

provides a full peripheral view

 Continuous flow improves vision during

therapeutic application

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 Conveniently located round clamp ensures good

control of distension medium valve

 Deploying the tool into the expandable canal

allows for continuous drainage for better

visualization during therapeutic interventions.

A monopolar electrode is used for

electrocoagulation, which is inserted into the

instrument and passes through its body. Its

movement can be controlled by the surgeon from the

other end. At the same time, an optical system is

introduced into the hysteroscope to allow the uterine

cavity to be displayed. It is also possible to control

the flow of the distension media by a circular clamp

which is at the bottom of the tool. The semi-rigid

case keeps the tool well-controlled while allowing

good manoeuvrability. The non-glossy surface

improves visibility on the video. The tools are made

of high quality surgical steel that guarantees bending

strength and torsion strength. Their average is 5 Fr

and 7 Fr. Visible spacing tapes on the case improve

the ability to control the depth of tool insertion.

(Schmid et al., 2013)

3 DESIGN OF A NEW TOOL FOR

HYSTEROSCOPY

The newly designed tool for hysteroscopy was

required to have better attributes than the one

currently used. It should shorten time of surgery,

should be able to remove larger polyps and myomas,

should have the ability to be used as scissors and it

should be compatible with the currently used

hysteroscopes.

3.1 Scissors Mechanism

The monopolar electrode has the disadvantage that it

cannot be used as simple scissors and thus make its

work more efficient. Therefore, attempting to use

hysteroscopy with bipolar electrodes, which would

form simple scissors in order to remove tissues

(polyps, myomas) and then coagulate tissues with

high frequency current. This basic idea led to the

first design of a new hysteroscopy operating tool

within this work.

The only limiting factor is the maximum tool

diameter that is 3 mm. This dimension is determined

by the size of the insertion canal on the

hysteroscope. For this reason a simple scissors

mechanism could not be used. With the small

dimensions of the individual rods, the correct

functionality of the tool or the pull system could not

be guaranteed. As shown in Figure 3, an electrode

which was necessary for the use of a high-frequency

current was placed at the ends of the individual arms

of the scissor mechanism. Figure 3 shows the

mechanism in an active coagulation position. For

better clarity, the prototype was expanded several

times to allow observation by the naked eye.

Another option was to use the eccentric length of the

individual arms, but this would require even more

pulling strings and better precision.

Figure 3: Designed scissors mechanism.

3.2 Joint Mechanism

The greatest emphasis has been put on simplifying

the entire design of the tool. Only one rod is used to

control the opening of the upper jaw. This

mechanism is connected with the control mechanism

that the surgeon has in his hand.

The tool is constructed as one fixed unit with one

movable part, the above-mentioned upper jaw. Its

outer diameter is 3 mm. The length of the entire tool

is not yet determined, it will depend on the further

development and length required to make the

operation convenient. The opening of the jaws is

possible by means of a peg.

The front of the tool is bevelled on both jaws to

ensure comfortable insertion into the insertion canal

on the hysteroscope. A groove is cut at the bottom of

the tool to pull the control rod out of the tool body. It

is assumed that sufficient flexibility of the control

rod is provided for an elastic bend, and this bending

will occur repeatedly. This movement results in the

opening of the upper jaw, respectively the sliding

movement of the rod is converted to a swinging

movement of the upper jaw. The jaws are now made

up of 9 rows of teeth that are knotted so that the

contact area between the jaws is as large as possible.

But this number is not final, it is designed only for

the prototype, the real tool can have more of these

rows, depending on the character of uterine tissue

that is supposed to be removed.

Design and Strength Analysis of Laparoscopical Tool for Electrocoagulation Surgery

271

Figure 4: Joint mechanism.

The only possible drawback of the tool is the free

space behind the upper moving jaw of the tool. By

pulling the tool out of the hysteroscope, the upper

jaw may jump around the edge of the insertion

channel, making it impossible for the tool to be

pulled out after surgery. This problem could be

partially avoided by chamfering the back edge of the

upper jaws. This proposed mechanism is shown in

Figure 4.

3.3 Spring Mechanism

The tool is again constructed as a single fixed unit

with a movable part. Its outer diameter is 3 mm. Its

length is not yet determined, it will depend on the

further development and length required to make the

operation convenient. The opening of the jaws is

made possible by means of a peg, which is not

located in the middle of the tool height, but is

located eccentrically. There were two reasons for

this change. The first reason was the possibility of a

larger jaw opening without the need to increase their

length. The second one was structural because of the

spring, so that its end could be better anchored in the

upper jaw. The front of the tool is bevelled on both

jaws to ensure comfortable insertion into the

insertion channel on the hysteroscope.

By using the spring as an operating tool control,

further simplification of the control would be

achieved, however, while meeting the essential

requirements, i.e. comfortable and reliable opening

of the jaws. A compression spring is used which is

connected to the control mechanism the surgeon has

in hand. When compressing this spring, the upper

jaw will open and the spring jaw closes when the

spring is released. This mechanism is shown in

Figure 5.

Figure 5: Spring mechanism.

3.3.1 Modified Spring Mechanism

This model does not differ much from the previous

one. The main change came in the jaws that formed

the series of teeth. At these locations, the groove was

cut to a depth of 1 mm throughout the jaw surface

and the resulting gap was filled with a conductive

surface (electrode) that had the same shape as the

jaw contact surfaces. In order to use high-frequency

current during coagulation. The electrodes continue

through the instrument body to the voltage source.

In addition, it was necessary to wrap the front

edges of the tool to avoid injuries during

manipulation in the uterine cavity.

The last change concerns the peg, which has

been reduced in size so that it is completely hidden

in the tool cavity. This proposed mechanism is

shown in Figure 6.

Figure 6: Modified spring mechanism.

3.4 Material Selection

The correct function of the device and its

components during the required lifetime is

conditioned not only by a suitable choice of the

production technology, but also by the proper design

and choice of the appropriate structural material

from which the component is to be made. The

requirements for the function of the structural

element directly determine its shape and its lifespan,

safety and also its price. (Kratochvíl et al., 2005)

The shape and function of the structural element

are limited by the conditions under which the

structural element has to function and the material

from which it is made. The conditions of operation

of the structural element, in particular the stress and

deformation, the temperature and the environment,

are decisive for the required properties of the

material intended for construction.

Appropriate choices are then determined by the

technology of manufacturing the components and its

price. There is also the issue of the safety factor and

it depends, in addition to the chosen strength

characteristic, on the importance of the construction

element in terms of reliability and lifespan of the

whole structure. (Webster, 1998)

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Subsequent selection of the appropriate material

for the specified design element is carried out using

a so-called design index s, according to which the

correct graph can be selected. For this application

the selected graph is Ashby's map. Ashby's maps are

divided by different types of loadings of structural

elements and other mechanical properties. Design

index s must be equal or less than the ratio of

strength σ

in MPa to density ρ in Mg/m

≤ σ

/ ρ (1)

The Ashby's map is best suited for the specified tool,

which includes the dependence of the maximum

load value (tension) on the maximum density value

of the material while maintaining the minimum

weight condition. According to Ashby's map, the

most appropriate material was selected, which is

Carbon Fiber Reinforced Polymer (CFRP).

(Kratochvíl et al., 2005)

4 STRENGTH ANALYSIS OF THE

DESIGNED TOOL

For strength analysis, it was necessary to determine

what strength the jaws of the operating tool would

be able to develop. That is why an experiment was

made to clarify the magnitude of this strength.

Surgical scissors were used in the experiment.

Furthermore, a stand was used to make the whole

system stable during work. Two clamps for holding

the scissors in the required position and height were

placed in a horizontal position. Two conductive steel

sheets were glued to the jaws to simulate the

coagulation electrodes. However, in order to avoid

the passage of the electric current into the scissors,

an electric insulator was added between the jaws and

the conductive surface. A terminal for the lead cable

was created at their outer end. One of these was

routed through a clutch that has a special gripping

device in order to use common feed wires into the

radio frequency wave generator (RF). The second

one was connected to a conductive pad that was

placed under the scissors' jaws and served as a

pickup area for organic fluids, then also connected to

the RF wave generator.

First of all, the lower jaw of the scissors has been

balanced to eliminate the gravitational force and

prevent spontaneous closure. A weight of 20 g was

used for this balance. Subsequently, the entire body

of the instrument was tested with a multimeter to

avoid possible undesired current flow and no high-

voltage current injuries. In order to add the weights

to the scissors, a holder was used which was

attached to the upper grip portion. By successively

adding weights of 100 g, 200 g, 500 g, 1000 g the

weight value required for sufficient tissue

coagulation was determined to be 1200 g. For the

first measurement, pork brisket without bone was

used as a sample tissue. It has a non-homogeneous

structure and it can represent the composition of

myomas and polyps in the uterine cavity. All

measured values are shown in Table 1. The table

consists of dimensions of the tissue sample, the

weight needed to compress the tissue to enable

proper coagulation, time to complete coagulation

and the percentage of fat in the used sample.

Figure 7: Experiment setup.

Table 1: Time and weight needed for tissue coagulation.

Tissue

dimensions

(mm)

Weight

(kg)

Time

(s)

Fat percentage (%)

5x14x3 1,2 8 80

5x15x2 1,2 2 30

5x15x2 1,2 5 50 - ideal

5x10x4 1,2 4 100

5x10x4 1,2 6 100

5x10x2 1,2 2 95

5x10x4 1,2 45 100 - tough

5 CONCLUSION

The aim of this work was to design a new

electrosurgical tool for hysteroscopy that would

replace a set of existing tools used for surgical

intervention with current hysteroscopes. The

proposed tool should further streamline the

performance, ensure greater speed, easier handling

and increased safety in use. It also has an ability to

be used as simple scissors with electrocoagulation. It

enables the surgeon to easily remove larger myomas

and polyps in the uterus.

The proposed tool was designed and a prototype

was created and tested. Strength analysis was further

performed and an experiment was designed to

Design and Strength Analysis of Laparoscopical Tool for Electrocoagulation Surgery

273

measure the strength needed to clamp the tissue and

time for proper coagulation. Pork brisket was used

as sample tissue. Depending on the tissue structure,

the time needed for coagulation was usually under 8

seconds.

The tool can be used as a replacement for

existing tools for hysteroscopes, it enables the

surgeon to remove myomas and polyps of various

sizes from the uterus cavity and its surroundings.

ACKNOWLEDGEMENTS

The work and the contributions were supported by

the project SV4508811/2101 Biomedical

Engineering Systems XIV'. This study was also

supported by the research project The Czech Science

Foundation (GACR) 2017 No. 17 - 03037S

Investment evaluation of medical device

development run at the Faculty of Informatics and

Management, University of Hradec Kralove, Czech

Republic. This study was supported by the research

project The Czech Science Foundation (TACR)

ETA No. TL01000302 Medical devices

development as an effective investment for public

and private entities.

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