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DESIGN AND EXPERIMENTATION OF SURGICAL DEVICES
FOR VOICE RESTORATION
CHNG CHIN BOON
(B.Eng. (Hons.). NUS)
A THESIS SUBMITTED
FOR THE DEGREE OF MASTER OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2011
Acknowledgement
Graduating from a purely mechanical background, the work I’ve done for this thesis
has been an eye opening experience. I would like to firstly express my gratitude to my main
supervisor, Dr. Chui Chee Kong for his kind patience and support throughout my candidature
which would not have been possible without his valuable guidance and encouragement. I
would also like to thank my co-supervisor, Senior Consultant Dr. David Lau Pang Cheng from
the Department of Otolaryngology, Singapore General Hospital, whose insightful feedback
and ideas provided not only the springboard for the projects, but often lead to the
conceptualization of most of the solutions presented.
I would also like to thank the all staff in Control and Mechantronics Laboratory 1 –
Mr Sakthiyavan s/o Kuppusamy, Mr Yee Choon Seng, Ms Ooi-Toh Chew Hoey, Ms Hamidah
Bte Jasman, Ms Tshin Oi Meng, whose friendly technical support and assistance provided a
pleasant and enjoyable environment to work in throughout my candidature.
Lastly, I would like to thank all fellow students and researchers in Dr Chui’s research
group for their advice, particularly Mr Yang Liang Jing and Mr Wen Rong, whose dedication
to their research has been a great source of inspiration.
The two projects report in this thesis is a collaboration between Singapore General
Hospital and National University of Singapore was supported in part by the National Medical
Research
Council
(Singapore)
under
Grant
NMRC/EDG/0006/2007
and
NMRC/EDG/0043/2008.
I
List of publications
Journal
C.B. Chng, D.P. Lau, J.Q. Choo, C.K. Chui, Bio-absorbable Micro-clip for Laryngeal
Microsurgery
Design
and
Evaluation.
Acta
Biomaterialia,
2012
(http://dx.doi.org/10.1016/j.actbio.2012.03.051).
D.P. Lau, C.B. Chng, J.Q. Choo, N. Teo, Bunte RM, C.K. Chui, Development of a micro-clip for
laryngeal microsurgery: Initial animal studies. The Laryngoscope. 2012; (Accepted).
J.Q. Choo, D.P. Lau, C.K. Chui, T. Yang, C.B. Chng, S.H. Teoh. Design of a mechanical larynx
with agarose as a soft tissue substitute for vocal fold applications. J Biomech Eng. 2010
Jun;132(6):065001.
Conference
C.B. Chng, C.K. Chui, D.P. Lau. A novel handheld device for tracheo-esophageal puncture and
prosthesis insertion. 2011 IEEE/SICE International Symposium on System Integration (SII
2011), 20-22 Dec 2011; 2011; Piscataway, NJ, USA: IEEE.
L. Yang, C. B. Chng, C.-K. Chui, D.P Lau. Model-based Design Analysis for Programmable
Remote Center of Motion in Minimally Invasive Surgery. 4th IEEE international Conference
on Robotics, Automation and Mechatronics 2010, Singapore, 2010.
II
Table of Contents
Acknowledgement ...................................................................................................................... I
List of publications ..................................................................................................................... II
Table of Contents ...................................................................................................................... III
Summary ................................................................................................................................... VI
List of figures ........................................................................................................................... VIII
List of tables .............................................................................................................................. XI
1.
Introduction ....................................................................................................................... 1
1.1. Background ..................................................................................................................... 1
1.1.1. Voice microsurgery .................................................................................................. 1
1.1.2. Voice restoration after total laryngectomy ............................................................. 3
1.2. Motivation and objective ................................................................................................ 5
1.3. Research scope and organization of thesis..................................................................... 6
2.
Literature review................................................................................................................ 7
2.1. Bio-absorbable clips for vocal fold wound healing ......................................................... 7
2.1.1. Vocal fold morphology ............................................................................................. 7
2.1.2. Laryngeal microsurgery............................................................................................ 8
2.1.3. Current methods for laryngeal wound healing........................................................ 9
2.1.4. Surgical clips ........................................................................................................... 12
III
2.1.5. Magnesium as the core material ........................................................................... 13
2.2. Device for TEP and prosthesis insertion ....................................................................... 14
2.2.1. TEP creation ........................................................................................................... 14
2.2.2. Transnasal esophagoscopy (TNE) guided TEP ........................................................ 15
3.
Bio-absorbable micro-clips for vocal fold wound closure ............................................... 18
3.1. Design requirements and considerations ..................................................................... 18
3.2. Selected design and implementation ........................................................................... 20
3.3. Experiments and results ............................................................................................... 22
3.3.1. In-vitro study .......................................................................................................... 22
3.3.2. Ex-vivo study .......................................................................................................... 24
3.3.3. In-vivo study ........................................................................................................... 26
3.4. Discussion...................................................................................................................... 32
3.4.1. Bioabsorption and biocompatibility of magnesium for the microclip ................... 32
3.4.2. Recommendation for future work ......................................................................... 34
4.
Device for TEP and voice prosthesis insertion ................................................................. 36
4.1. Design requirements and proposed solution ............................................................... 36
4.2. Designs .......................................................................................................................... 37
4.2.1. Initial design ........................................................................................................... 37
4.2.2. Handheld device .................................................................................................... 40
IV
4.2.3. Manipulator system ............................................................................................... 45
4.3. Experiments and results ............................................................................................... 50
4.3.1. Manual device ........................................................................................................ 50
4.3.2. Handheld device .................................................................................................... 52
4.4. Discussion...................................................................................................................... 53
4.4.1. Recommendations and future work ...................................................................... 53
5.
Conclusion ........................................................................................................................ 57
6.
References ....................................................................................................................... 58
7.
Appendix I –Technical drawings....................................................................................... 63
7.1. Micro-clip ...................................................................................................................... 63
7.2. Manual TEP device ........................................................................................................ 64
7.3. Handheld TEP device..................................................................................................... 69
7.4. Calculation of the end effector position for the robotic manipulator .......................... 73
V
Summary
Voice production is an ability that allows us to verbally communicate our thoughts
and ideas. The total loss of such a crucial skill has enormous psychosocial and economic
consequences on patients’ lives. Two common procedures in head and neck surgery for the
restoration of voice are voice microsurgery and implantation of a voice prosthesis for
patients after total laryngectomy. This thesis thus presents details of the development and
experimental evaluation of devices to aid respectively in the two surgical procedures – 1)
bio-absorbable micro-clips to aid in vocal fold wound closure and 2) a tracheoesophageal
puncture and voice prosthesis insertion device for immediate voice restoration.
For voice microsurgery, surgical removal of benign lesions often results in an incision
in the vocal folds. In order to reduce scarring, the edges of the wound need to be
approximated in order for healing by primary intention. Current techniques for vocal fold
wound include the usage of micro-sutures or fibrin glue. While current methods have been
found to provide good treatment results, each are limited by different constraints which
increase procedural difficulty and time. Hence, based on combining the ease and efficiency
of using fibrin glue with the precision and security of micro-sutures, a novel bio-absorbable
micro-clip made from magnesium is specifically designed to reduce technical complexity in
achieving apposition of epithelial flaps, possibly providing comparable wound holding and
healing properties to current methods. The micro-clips were tested in an in-vivo survival
study with a pig model for their ease of application, bio-absorption and bio-compatibility.
Experimental results revealed a lack of significant inflammation and achievable bioabsorption rates.
VI
For the implantation of a voice prosthesis for patients after total laryngectomy, a
tracheoesophageal puncture (TEP) is used to create a fistula in which a voice prosthesis can
be inserted. Traditionally, this procedure is performed in an operating theatre under general
anaesthesia. However, the recent trend has been towards in-office unsedated techniques
which leverage the visual advantages transnasal esophagoscopy (TNE) provides. Even so,
due to difficulties in appropriately sizing a voice prosthesis at the time of TEP, immediate
voice restoration for patients is seldom achieved. A device consisting of two concentric
metal cannulae is therefore developed to insert the voice prosthesis (VP) accurately and
immediately at the time of initial puncture. The device and its various embodiments were
also tested in-vivo to evaluate their feasibility. Experimental results showed that with the
devices, appropriately sized voice prosthesis could be easily inserted at the time of TEP,
enabling immediate voice restoration.
The devices described in this thesis have the potential to improve current methods
of voice restoration. Both procedural time and recovery time can be reduced, cumulating in
cost savings for patients.
VII
List of figures
Figure 1 – Common tools used in laryngeal microsurgery. (Left) Laryngoscopes with a Fibre
optic light carrier. (Right) Microlaryngeal forceps and suction tubing. ..................................... 2
Figure 2 - Before and after Laryngectomy. Images courtesy of InHeath Technologies [8]
which supplies Blom-Singer voice prostheses. .......................................................................... 3
Figure 3 – Tracheoesophageal Voice Prosthesis [8] .................................................................. 4
Figure 4 - Vocal fold morphology (Coronal view). Picture adapted from [30]. ......................... 7
Figure 5 – Microflap technique in practice, (Left) after removal of benign lesion and (Right)
redraping of microflap. .............................................................................................................. 9
Figure 6 – From Baxter [48] (Left) TISSEEL fibrin glue and applicator. (Right) FIBRINOTHERM
heating and stirring device. ..................................................................................................... 11
Figure 7 - Mini-Trach II – Seldinger Portex Minitracheotomy Kit [64] ..................................... 16
Figure 8 - Initial shapes of clips. ............................................................................................... 19
Figure 9 - Loaded Micro-clips in a typical microlaryngeal forcep ............................................ 20
Figure 10 – CAD drawing of clip (Isometric view) .................................................................... 21
Figure 11 - Micro-clip design. (Left) Before application. (Right) After application. ................. 22
Figure 12 - The weight gain of specimens (%wt) and pH of m-PBS plotted as functions of
corrosion time. ......................................................................................................................... 23
Figure 13 - Mounted trachea on ex-vivo setup ....................................................................... 25
Figure 14 – Ex-vivo experiment with excised larynx. (Left) Applied micro-clips within larynx.
(Right) Tensioning of micro-clips exhibiting their security. ..................................................... 26
Figure 15 - In-vivo setup .......................................................................................................... 28
Figure 16 – Microscopic view of the micro-clips after application in-vivo. ............................. 30
VIII
Figure 17 – Histological results showing inflammatory reaction to the micro-clips. (Left) Unpolished magnesium micro -clips. (Right) PCL coated micro-clips. ......................................... 31
Figure 18 – Applicator design. ................................................................................................. 34
Figure 19 – Non-indwelling voice prostheses from (Left) Provox NID [83] (Right) Blom-Singer.
................................................................................................................................................. 38
Figure 20 – Initial design. (Left) CAD drawing of 1) the measurement cannula and 2) its
adaptor cannula. (Right) Fabricated prototype used to test solution concept. ...................... 39
Figure 21 – The finalized design. From left to right, the modified measurement cannula,
handle, loader and plunger. ..................................................................................................... 40
Figure 22 – 3D CAD drawing of the handheld device. ............................................................. 41
Figure 23 – (a) Loaded puncture tool before puncture. (b) Loaded puncture tool after the
puncture stroke. (c) Measurement cannula after retraction stroke. Main body is concealed
for better view. ........................................................................................................................ 43
Figure 24– Loaded insertion tool with measurement cannula (a) just before voice prosthesis
insertion. (b) after the insertion stroke. .................................................................................. 44
Figure 25 – Fabricated main body of the handheld device with the measurement cannula
and puncture tool. (Left) After the puncture stroke. (Right) After the insertion stroke. ........ 45
Figure 26 - 3D CAD drawing of manipulator system with handheld device mounted. .......... 46
Figure 27 - Frame assignment for the manipulator with an alternate end effector for gripping
a trocar. .................................................................................................................................... 46
Figure 28 – Fabricated manipulator system for handheld device ........................................... 48
Figure 29 – User interface of manipulator system. (Left) Teleoperation mode and (Right)
predefined mode. .................................................................................................................... 48
Figure 30 – Simulated environment. (Left) Matlab simulation of the configuration of the
manipulator. (Right) Sub-manipulator mounted with an earlier version of the handheld
device ....................................................................................................................................... 49
IX
Figure 31 – In-vivo experiment. (Left) Simulated tracheostome. (Right) TNE system. ........... 50
Figure 32 - Experimental evaluation of the manual device. (A) Palpitation of anterior tracheal
wall. (B) Initial puncture with needle. (C) Guide wire insertion. (D) Removal of needle. (E)
Insertion of dilator with manual device. (F) Insertion of prosthesis after remove of dilator. (G)
Removal of measurement cannula. (H) External view of the surgical site. ............................. 51
Figure 33– Handheld device used to Inserted the voice prosthesis within the fistula. (Left)
Measurement cannula within fistula. (Right) Inserted duckbill voice prosthesis.................... 52
Figure 34 – Schematic diagram of the handheld device. ......................................................... 54
Figure 35– In-vivo force data of 14G needle insertion through posterior tracheal wall and
anterior esophageal wall. ........................................................................................................ 55
X
List of tables
Table 1 – Summary of In-vivo Experimental Results................................................................ 29
Table 2 ̶ DH parameters for the manipulator ......................................................................... 47
XI
1. Introduction
This chapter introduces the relevant background information, states the motivation
and defines the objectives of the projects in this thesis.
1.1. Background
Voice production is an essential skill that enables humans to communicate
information and convey our emotions. Generation of the sound waves required for speech
starts in the larynx, where the vocal folds vibrate due to fluctuations in pressure. However,
the larynx is a fragile organ susceptible to various disorders which can result in the reduction
or loss of voice capabilities. In moderate cases like the growth of benign vocal fold lesions,
voice microsurgery is commonly used for treatment. In more severe cases like total
laryngectomy, voice restoration methods are required instead.
1.1.1. Voice microsurgery
One of the most common causes of voice disorders are benign vocal fold lesions
such as nodules, polyps and cysts. While these lesions are non-cancerous, they may result in
impaired vocal fold closure and vibration, and reduction of voice quality. Treatment is
divided into two main categories based on the surgical instruments used – either laser
surgery or cold surgery. In laser surgery, a CO2 laser is used to ablate tissue and for
coagulation of the target region [1]. Together with a micro-manipulator for precise cutting,
the reduced blood loss during laser surgery enables a relatively clear view of the surgical
field. Although studies have found no significant difference in surgical outcomes between
laser and cold surgery [2-4], risk of thermal damage to surrounding tissues is still dependent
on familiarity with the equipment and surgical technique. This coupled with the increased
1
cost of equipment, maintenance, additional personnel and their training [1], has maintained
the relevance of traditional “cold” voice microsurgery techniques. Cold surgery allows for
tactile feedback and is better utilized in techniques like the micro-flap excision of benign
vocal fold lesions [4].
Figure 1 – Common tools used in laryngeal microsurgery. (Left) Laryngoscopes with a Fibre optic light carrier.
(Right) Microlaryngeal forceps and suction tubing.
Laryngeal microsurgery involves operating on the vocal folds under general
anaesthesia [5], where access to the vocal folds typically utilizes suspension laryngoscopy [6].
A rigid laryngoscope (Figure 1) inserted via the patient’s oral cavity provides a direct view of
the vocal folds. The laryngoscope is suspended over the patient’s chest to free up the
surgeon’s hands for operating. A binocular operating microscope is used to provide
magnification. Due to the prohibitive space constraints of laryngoscopes, microlaryngeal
instruments are thin and long to access the lesion while maximizing vision of the surgical
field (Figure 1). A significant level of dexterity is needed to handle the microlaryngeal tools,
especially considering the fragile structure of the vocal fold. Epithelial micro-flaps may be
created and elevated with micro-laryngeal instruments during surgery and these micro-flaps
require re-approximation on completion of the procedure. Current techniques for reapproximation are the focus of this thesis and will be discussed in the Chapter 2.
2
1.1.2. Voice restoration after total laryngectomy
In the medical field of otolaryngology or ENT (Ear, nose and throat), one of the most
commonly diagnosed malignancies in Singapore is laryngeal cancer [7], often the result of
heavy smoking and alcohol abuse. Total laryngectomy (TL) is often used as surgical
treatment for locally advanced laryngeal and pharyngeal cancer, in which the larynx is
detached from the trachea and excised. A tracheostome is subsequently constructed with
the remaining trachea for breathing (Figure 2).
Figure 2 - Before and after Laryngectomy. Images courtesy of InHeath Technologies [8] which supplies BlomSinger voice prostheses.
There are a number of options available for voice rehabilitation, ranging from
oesophageal speech, electrolaryngeal speech and prosthetic valve speech. Prosthetic voice
restoration provides the closest approximation to normal laryngeal voice and is considered
to be the gold standard of choice [9-11]. Prosthetic voice restoration involves the
implantation of voice prosthesis in a surgically created fistula between the posterior tracheal
3
wall and the anterior esophageal wall (Figure 3). This fistula is created by means of a
tracheoesophageal puncture (TEP) which can be carried out either as a primary procedure at
the time of TL or as a secondary procedure in a subsequent surgery [12-15]. In difficult
circumstances like if primary surgery is extensive and requires free flap or gastric pull-up
reconstruction, after heavy neck irradiation, or when alternative voicing techniques
including primary TEP have failed [16], secondary TEP has been found to prevent potential
complications such as cervical cellulitis, mediastinitis and salivary leakage [17-22] which may
adversely affect healing of the TL site.
Figure 3 – Tracheoesophageal Voice Prosthesis [8]
Traditionally, secondary TEP is performed in an operating theatre with rigid
esophagoscopy and under general anesthesia. Advancements in endoscopy have allowed
the development of transnasal esophagoscopy (TNE) and together with various secondary
TEP techniques, there is an increasing trend towards unsedated in-office TEP [18, 23-27]. Inoffice TEP avoids risks of general anesthesia and those associated with rigid esophagoscopy
4
such as esophageal perforation, and oral injury [28]. It enables cannulation of the esophagus
in patients with limited neck extension or stenosis of the neopharynx [29], allows rapid
recovery and decreases the need for patient monitoring. Also, performing the procedure in
an outpatient, office-based setting reduces patient cost. A stent in the form of a nasogastric
tube or catheter is often left in the fistula for one or two weeks while it matures. After which,
the patient returns to have a voice prosthesis sized and inserted, restoring his ability to
speak.
1.2. Motivation and objective
Our ability to express and communicate our thoughts and ideas is one that many of
us cannot afford to lose. The disabling psychosocial and economic consequence of losing
one’s voice is an ordeal for many patients and it is of great interest to reduce or mitigate
such issues/problems. This thesis is split into two main studies - voice microsurgery and
voice restoration.
For voice microsurgery, the main objective is to develop a small clip to be applied to
close incisions on the vocal fold, with at least comparable wound holding and healing
properties to current methods. Based on combining the ease and efficiency of using fibrin
glue with the precision and security of micro-sutures by specifically designing the micro-clip
and application technique to reduce technical complexity in achieving apposition of
epithelial flaps, it is hoped that such surgical micro-clips have the potential to reduce
procedure time and vocal fold scar, cumulating in better surgical outcomes and cost savings
for patients.
5
For voice restoration, an improvement in the current voice restoration method of
voice prosthesis insertion is required. By developing a device to insert the voice prosthesis
immediately at the time of initial puncture and leveraging on the visual advantages TNE
provides, it is hoped that such a device allows immediate voice restoration for patients,
reducing recovery time and thus translating to lower costs.
1.3. Research scope and organization of thesis
This study focuses on the design and development of two separate surgical devices
to aid the restoration of voice in patients in both voice microsurgery and total laryngectomy.
This thesis is organized as follows: Chapter One introduces the background of the research
topic as well as the motivation and objectives of the project. Chapter Two reviews the
current state of the art and related topics. Chapter Three presents the development of the
bio-absorbable micro-clips for would closure and their evaluation in ex-vivo and in-vivo
experiments. Chapter Four presents the development of various versions of the device for
TEP and voice prosthesis insertion and their evaluation in-vivo. Finally the contributions of
this work are concluded in Chapter Five.
6
2. Literature review
A range of relevant topics was reviewed to better understand and appreciate the
advantages and limitations in the current state of the art.
2.1. Bio-absorbable clips for vocal fold wound healing
2.1.1. Vocal fold morphology
Current voice microsurgery techniques are based on Hirano’s discovery of the
layered structure of the vocal folds [5, 30, 31]. Based on his microscopic work, the vocal fold
was found to be composed of three well defined layers - the epithelium, lamina propria and
vocalis muscle. The lamina propria was further subdivided into 3 layers, the superficial layer
of the lamina propria (SLLP), intermediate layer and deep layer. Figure 4 illustrates the
morphology of an adult vocal fold.
Epithelium
Cover
Superficial Layer
Intermediate Layer
Lamina
Propria
Deep Layer
Vocalis
Muscle
Interface
Body
Figure 4 - Vocal fold morphology (Coronal view). Picture adapted from [30].
In the SLLP, elastin and collagen fibres are loosely arranged within a matrix, whereas
dense elastin fibres make up most of the intermediate layer. Collagen is densely packed in
7
the deep layer, providing most of the support for the lamina propria [30]. Hirano also
proposed a cover-body concept, providing an explanation for the vibratory characteristics of
the vocal fold. Based on his theory, the cover (consisting of stratified squamous epithelium
and the underlying SLLP) is attached to the body (consisting of the vocalis and
thyroarytenoid muscles) by an elastic interface or ligament (composed of the intermediate
and deep layers of the lamina propria), with an increasing stiffness from superficial to deep.
This allows the cover to oscillate independently due to its elastic characteristics, resulting in
the mucosal wave seen on stroboscopy and most of the vibratory dynamics required for
good voice production and phonation [31].
The vocal fold is a layered structure, and the depth from the epithelial surface to
vocal ligament layer is approximately 1 mm [32, 33]. Surgical dissection is usually limited to
the surface layers including the epithelium and superficial lamina propria.
2.1.2. Laryngeal microsurgery
Early treatments for benign vocal fold lesions consisted of stripping (deepithelialization) of the entire vocal fold [34]. The healing process after this method of
treatment often results in significant vocal fold scar formation which causes a change in the
stiffness and viscoelastic layered structure of the lamina propria. This inhibits normal
vibration of the vocal fold and can cause significant dysphonia and possible glottic
incompetence. However with the discovery by Hirano of the layered structure of the vocal
foldand its implications on healing, treatment is now focused on preserving as much of the
normal vocal fold structure as possible [35-38]. Avoiding injury to the deeper structures is
important during voice microsurgery to minimize vocal fold scarring and persistent postoperative hoarseness.
8
Figure 5 – Microflap technique in practice, (Left) after removal of benign lesion and (Right) redraping of
microflap.
The microflap technique has been accepted as the standard approach for cold
surgical removal of benign vocal fold lesions [37, 39, 40], achieving the main principles of
vocal fold surgery by minimal tissue excision and minimal trauma to SLLP and epithelium.
This technique typically involves the initial creation of an epithelial incision beside the lesion.
Blunt dissection is used to elevate the microflap while taking care to minimize trauma to the
deeper layers of the lamina propria. Only pathologic tissue is excised and the microflap is
then reapproximated [34] as seen in Figure 5.
2.1.3. Current methods for laryngeal wound healing
Typically following excision of the lesion, the microflap is redraped to promote
primary healing. If there is loss of epithelium or dislodgement of the microflap, then healing
can occur by secondary intention. In this case, granulation tissue formation and epithelial
migration occur and there is correspondingly more scar tissue formation [37, 41]. Voice rest
is usually prescribed after surgery [42], but even with a totally compliant patient, apposition
of epithelial flaps edges can be difficult to maintain. More advanced techniques for
apposition of epithelial flaps during laryngeal microsurgery include using micro-sutures to
re-approximate the edges [35, 41, 43] and the application of fibrin glue to seal the flaps,
improve wound closure and minimize scar tissue formation [5, 44-47].
9
2.1.3.1. Micro-sutures
The use of micro-sutures in vocal fold wound closure was proposed by Woo et al. in
1995, hypothesizing that micro-sutures would allow precise positioning of wound edges and
maintenance of the approximation [41]. This would reduce exposure of the wound site and
permit primary healing to occur. They carried out the procedure in 18 patients, finding
improved voice results after surgery.
As there was no control group and basis for
comparison in Woo et al.’s study, Fleming et al. attempted to compare the amount of scar
formation with and without micro-sutures in a canine model [35]. A small sample group of 4
dogs were used, with bilateral micro-flaps defects created in each dog. 6-0 fast absorbing
gut sutures were used to close the microflap on only one side, leaving the contra-lateral side
unclosed. The amount of scar was evaluated between 39 and 49 days post surgery. Unsutured vocal folds were found to have at around 75% larger scar formation than sutured
vocal folds, concurring with Woo et al.’s hypothesis that the use of microsutures improves
postoperative wound healing.
However, suturing of tissue is still challenging due to restrictions imposed by the
laryngoscope. These restrictions include limitation of instrument movement to 4 degrees of
freedom, reduced force feedback and loss of stereopsis. High level of skill is required during
suturing and surgeons must exercise care not to grasp the deeper structures of the vocal
folds. Fleming et al. [35] also identified the length of time required for suture placement as
the main disadvantage of this technique, suggesting that practice and familiarization with
the technique using larger sutures before actual surgery could help mitigate the learning
curve.
10
Tsuji et al. recently proposed an improvement to the microsuture technique [43] by
pre-tying a small length of 4-0 non-absorbable nylon suture to the free end of a 7-0
absorbable suture. The nylon acted as an anchor at the epithelial surface, preventing the
thread from escaping and removing the need for an assistant surgeon to maintain tension
on the free end of the suture. This improved the ease of performing the technique. Their
new technique was tested on human cadaveric larynges for a total of 10 sutures and they
reported a placement time of 5 to 7 minutes per suture.
2.1.3.2. Fibrin glue
Despite good wound healing results demonstrated by micro-sutures, many surgeons
prefer using adhesives to hold down epithelial flaps to achieve wound closure. Tissue
adhesives such as cyanoacrylates and fibrin glue have been used [44] and are easier to apply
than sutures. Tisseel from Baxter is one such fibrin glue that is current used. Figure 6 shows
the current tools from Baxter used to prepare and apply fibrin glue to vocal fold wounds.
Figure 6 – From Baxter [48] (Left) TISSEEL fibrin glue and applicator. (Right) FIBRINOTHERM heating and
stirring device.
The components of TISSEEL from Baxter needs to be firstly, diluted based on
required concentration and heated before loading each into its allocated syringes for
11
application. Its applicator consists of a Y-tubing which combines both components and
expels it through a blunted hypodermic needle onto the application site.
A potential limitation of tissue adhesives includes increased scar tissue formation if
glue accumulates between the epithelial edges preventing proper approximation, or by
adhering the epithelium to the underlying connective tissue without proper reformation of
the intervening layered structure. Depending on the concentration used, the lack of tensile
strength of the adhesive is another possible concern. Fibrin glue can take several minutes for
initiation of curing and several hours to develop its full strength. Especially during the curing
phase, it may not possess sufficient tensile strength to withstand rupture of its bond [41].
Conversely, rapid curing can also restricts the surgeon from re-apposing malpositioned flaps,
resulting in even more scarring. Lastly, as the vocal folds vibrate at high frequencies during
speech, constant shearing against the adhesive glue causes wear and the resultant debris
may impede the vibratory properties of the vocal fold. Healing by secondary intention and a
broader scar may also occur as a result.
2.1.4. Surgical clips
While surgical clips or staples have been used in various areas of the body, they have
not been described previously for use in vocal folds. Nevertheless, as an alternative to time
consuming suturing, surgical staples provide a rapid solution to closure of long incisions [49].
A number of materials have also been studied in the design of surgical clips. Stainless steel
clips and newer materials such as titanium and tantalum have been used in areas where
surgical dissection is difficult, such as ligating the cystic duct and artery in laparoscopic
cholecystectomy[50]. However, major limitations of these materials include significant
foreign body reaction, poor holding power and significant interference with roentgenologic
12
studies like computerized tomography (CT) and magnetic resonance imaging (MRI), making
them unfavourable for application[51-54]. The introduction of ligating clips manufactured
from novel polymers such as polydioxanone in laparoscopic cholecystectomy helped to
address these limitations. These clips are completely absorbed in the process of ester bond
hydrolysis over a period of 180 days and the by-products are excreted by urine. Moreover,
these clips produce minimal tissue reactivity with good adhesion, and are radiolucent [54].
However, earlier studies with such clips proved them to be unsuitable for our requirements,
as they could not provide adequate structural strength due to the minute size of the microclips.
2.1.5. Magnesium as the core material
There have been a number of reviews on the potential and viability of magnesium as
a biomaterial [52, 55, 56]. Most of these studies, which focus on the use of magnesium in
orthopaedic implants and bio-absorbable vascular stents, concentrate on improving its
mechanical properties by alloying with various elements. Zhang et al. [57] reported
significant improvement of both biocompatibility and mechanical properties using Zn as an
additional alloying element to Mg-Si. Gu et al. [58] reported good biocompatibility of
magnesium with various alloying elements, recommending Al and Y for stents and Al, Ca, Zn,
Sn, Si and Mn for orthopaedic implants. Drynda et al. [59] developed and evaluated fluoride
coated Mg-Ca alloys for cardiovascular stents, reporting good biocompatibility and better
degradation behaviour.
However, as pure magnesium corrodes too quickly in the low pH environment of
physiological systems, much effort has also been placed into developing alloys or coatings to
limit its degradation behaviour [55]. Rosalbino et al. [53] reported improved corrosion
13
behaviour of Mg-Zn-Mn alloys for orthopaedic implants. Kannan et al. [60] studied the
corrosion of AZ series (Al and Zn) magnesium alloys with the further addition of Ca,
reporting significantly improved corrosion resistance with a reduction in mechanical
properties (15% ultimate tensile strength and 20% elongation before fracture). Zhang et al.
[61] reported the use of dual layer coatings of hydroxyapatite to considerably slow down the
degradation of 99.9% pure magnesium substrates without heat treatment.
2.2. Device for TEP and prosthesis insertion
2.2.1. TEP creation
Several techniques for unsedated in-office secondary TEP have been described.
Desyatnikova et al. carried out blind puncture using a 16-gauge needle [24]. An esophageal
dilator swallowed by the patient provided tactile feedback to confirm needle entry into the
esophagus, and also protected the posterior esophageal wall from trauma by the needle.
With the needle in place a guide-wire was passed through it after which the esophageal
dilator was withdrawn. A separate dilator passed over the guide-wire was followed by the
prosthesis. Direct laryngoscopy provided some degree of visualization.
Erenstein and Schouwenburg also performed blind puncture but used an
endotracheal tube through the mouth to dilate the esophagus[62]. A flexible
nasopharyngoscope passed into the endotracheal tube trans-illuminated the posterior
tracheal wall to indicate its position. With the cuff inflated to hold the endotracheal tube in
position, a trocar was passed through the posterior tracheal wall into the esophagus and the
endotracheal tube. A guide-wire passed through the trocar was brought out of the mouth
through the endotracheal tube. A dilator placed on the tracheal end of the guide-wire was
14
used to enlarge the fistula by withdrawing the guide-wire through the mouth. The prosthesis
was then inserted through the dilated tract.
2.2.2. Transnasal esophagoscopy (TNE) guided TEP
TNE guided TEP was first described in 2001 by Belafsky et al. [26]. In their case
report, TNE allowed the replacement of a poorly placed TEP under direct vision.
Subsequently, Bach et al. [18] described their technique in 2003. In their method, TNE was
used to visualize the puncture site under local anesthesia. The puncture position was
marked with a 22-gauge needle, and a stab incision was made along the same tract and
widened with a hemostat. Following this, a TEP prosthesis was placed using the gel cap
technique. Two additional series on TNE-guided TEP were identified in the literature. In 2007,
Doctor reported 11 patients undergoing TNE-guided TEP following TL [16]. The success rate
for secondary TEP placement was 91%. One patient was complicated by bleeding from the
puncture site which was arrested with silver nitrate cautery. Doctor described using a
straight needle to guide placement of the puncture site and performed the puncture with a
size 11 blade. In 2009, LeBert studied 39 patients undergoing TNE-guided TEP [23]. The
overall success rate was 97% and included patients who had undergone TL (64% of cases), TL
with partial pharyngectomy (21% of cases), and microvascular flap reconstruction (36% of
cases). Radiotherapy or cricopharyngeal myotomy did not significantly impact the success of
TEP placement, complications associated with TEP placement, TEP prosthesis usage or
speech intelligibility. Le Bert described making the puncture directly with a size 11 blade
after visualizing indentation of the posterior tracheal wall by ballotment.
The main advantage of TNE-guided TEP over earlier techniques is the ability to
visualize the esophageal lumen. An additional benefit is that the discomfort of swallowing a
15
dilator or endotracheal tube is avoided. Visualizing the esophagus during TEP has the
following advantages: 1) False tract formation can be prevented. 2) Viewing the needle tip
within the esophagus helps minimize trauma to the posterior esophageal wall [18]. Care
must still be taken during initial stab incision as the anterior esophageal wall can tent up
against the posterior wall despite air insufflation of the esophagus. However, trauma from
the initial insertion is usually insignificant, and once the needle tip is seen intra-luminally, its
position can be controlled. 3) The puncture can be directed to a more open part of the
esophageal lumen. Avoiding constricted areas may improve airflow during subsequent
voicing which may have implications on improving voice outcome. To achieve optimal
needle placement, the puncture may need to be directed sideways as esophagus and
trachea are sometimes off-centre in relation to the sagittal plane. 4) Finally, anatomical
distortion resulting from reconstruction may be easier to negotiate using flexible rather than
rigid esophagoscopy. In addition, Sidell et al. reported that inoffice TEP and voice prosthesis
sizing and placement were better and resulted in a reduction in follow up visits to resize the
prosthesis [63].
Figure 7 - Mini-Trach II – Seldinger Portex Minitracheotomy Kit [64]
16
In 2010, Lau et al. described the use of the mini-tracheostomy kit to perform TNEguided TEP [25], reporting the additional benefit of minimizing bleeding and trauma to
surrounding tissue by dilating instead of incising tissue [26]. The Seldinger technique used in
the paper dilates tissue over a guide-wire, practically eliminating the risk of creating a false
passage, which can still occur when inserting a tube or prosthesis through an incision
without guide-wire. The downward-angled Tuohy needle in the kit (Figure 7) helps ensure
the guide-wire is directed downwards into the esophagus, and the dilators in the minitracheostomy kit are curved and softened which minimizes soft tissue trauma. These
features allow the procedure to be completed safely and rapidly within several minutes.
Finally, nearly all instruments within the kit are utilized, making it a well contained unit and
minimizing wastage.
17
3. Bio-absorbable micro-clips for vocal fold wound closure
This chapter will focus on the design, implementation and evaluation of bioabsorbable micro-clips for vocal fold wound closure. First, the design requirements are
established and proposed solution is presented in Section 3.1. The implementation of the
micro-clips is then presented in Section 3.2. Experimental evaluation of the micro-clips is
then carried out in Section 3.3, concluding with the discussion of the feasibility of the
prototype micro-clips in Section 3.4.
3.1. Design requirements and considerations
As discussed in the background and literature review, there is a need to develop a
device that reduces the technical complexity of vocal fold wound closure and in turn the
procedure time. A summary of the main requirements of the micro-clips are thus listed
below:
1. Able to dissolve/degrade within 2 weeks
2. Non-toxic, little or no adverse tissue reaction, both on vocal fold or when inhaled.
3. Able to adequately secure edges of epithelial flaps and able to withstand high
vibration frequencies and shearing stresses during phonation.
4. No adverse mechanical effects such as mucosal tearing and injury to contra-lateral
vocal fold
5. Easy to apply and remove in case of mal-positioned flaps.
From the studies reported in the literature review, magnesium has been
demonstrated to have good bio-absorbability and biocompatibility. Wound healing by
primary intention takes approximately 1 week for collagen synthesis to occur and initial
wound strength to develop [65]. Based on this knowledge of wound healing, ideally the
18
micro-clip should retain most of its tensile strength for at least one week and be fully
absorbed by the end of the second week. In addition magnesium is a relatively soft, ductile
and malleable metal. Thus with requirements 1-3 in mind, magnesium could be used as the
core material to develop a small clip to be applied to close incisions on the vocal fold, with
comparable wound holding and healing properties to current methods. Use of additional
coating like PCL can possibly reduce inflammation. However, detailed design of the material
composition to be used in the micro-clip and its coating is not within the scope of this thesis.
Figure 8 - Initial shapes of clips.
Proper design of the micro-clips’ exterior shape is needed to fulfill requirements 4
and 5. Sharp corners in the design should be avoided as they attract fibrous growth around
the micro-clip and could antagonize the wound during vocal fold vibration, resulting in
chronic inflammation and prolonged healing. As discussed earlier, the vocal fold is a layered
structure and the depth from the epithelial surface to vocal ligament layer is approximately
1 mm [32, 33]. Surgical dissection is usually limited to the surface layers including the
epithelium and superficial lamina propria. Damage to the deeper layers including the vocal
ligament or muscular layer can increase fibrosis and scarring [66], with resulting disruption
of the mucosal wave and diminished voice quality [67, 68]. Hence the anchors of the microclip has to be less than 1mm deep to minimize penetration of the deeper layers. The overall
size of the micro-clip has to be as small as possible so as not to impede or dampen vibration
of the vocal fold, while having a opening large enough to cover the incision gap. Figure 8
shows the various shapes of clips explored. Each design was evaluated from its ease of
19
loading to application with a typical micro-laryngeal surgical forceps (2mm cupped, Jako) in
Figure 9.
Figure 9 - Loaded Micro-clips in a typical microlaryngeal forcep
The application procedure can thus be decomposed into a few steps:
•
Load micro-clip either manually or with the use of a clip holder designed for easy
loading.
•
Insert applicator through laryngoscope.
•
Orientate micro-clip over vocal fold wound, ensuring micro-clip width is
perpendicular to wound line and its ends do not poke into the wound.
•
Deploy micro-clip into vocal fold by squeezing handle.
3.2. Selected design and implementation
The selection of the shape was based on 1) the ease in which the microclip could be
loaded, 2) held within the cupped forceps, 3) the size of the opening between the distal ends
of the micro-clip, 4) the final shape of the micro-clip after application. Early experiments
with the various shapes of the micro-clips highlighted the dependence of the final shape on
the initial shape of the micro-clips, especially if the forceps is not closed fully. This in
20
particular is important as enclosing the forceps fully would obscure the application site,
possibly even resulting in misaligned epithelial flaps or over-compressing and damaging the
wound. The final elliptical shape seen in Figure 10 below was selected as it was found to
provide the best and most stable fit within an open 2mm microlaryngeal forceps, providing
enough friction preventing the clip from slipping and changing orientation when
transporting it to the application site. Upon clamping, it was found to deform into the most
desirable circular shape without sharp corners.
Figure 10 – CAD drawing of clip (Isometric view)
Rectangular strips (6.96mm long, 0.42mm wide and 0.35mm thick) of magnesium
(with purity of 99.5%) (Sigma Aldrich, 13103) were cold-sheared with a stainless steel paper
cutter at an incident angle of 30°. The implemented micro-clip design is shown in Figure 11
below. Specifications of the micro-clip are as follows – a semi-elliptical shape with major
diameter of 3.5mm and minor diameter of 2mm. When applied and enclosed, the micro-clip
should form a profile within a circle of diameter 2mm, with the lower half of the micro-clip
embedded within the vocal fold.
21
Figure 11 - Micro-clip design. (Left) Before application. (Right) After application.
For surface modification of the micro-clips, poly-ε-caprolactone (PCL) with molecular
structure -(COO CH2 CH2 CH2 CH2 CH2)n- and average molecular weight of 80,000 (Sigma
Aldrich, 440744) was used to coat some of tshe specimens. A 3% weight-volume
concentration of PCL was dissolved in methylene chloride and the magnesium specimens
were immersed in the PCL solution at room temperature for 45 seconds. The specimens
were then air dried at room temperature.
3.3. Experiments and results
3.3.1. In-vitro study
While the works mentioned earlier [53, 55, 57-61] show that magnesium degrades
rapidly, further investigation on the corrosion properties of pure magnesium and PCL coated
specimens in a simulated environment of the vocal folds was carried out to ascertain their
speed of degradation. Work done in this section was not of the author, but is summarized
here with permission from Choo Jun Quan for completeness of the study [69].
Magnesium, PCL coated magnesium samples were grouped and gravimetrically
weighed collectively in batches of 10 samples and averaged, up to precision of 0.1mg. The
immersion test was carried out in 1X concentration of PBS (Sigma Aldrich), added with
22
0.92g/L of Xanathan gum, as simulated artificial saliva. The concentration of NaCl is
maintained at 8g/L as compared to the documented concentration of Xialine1 artificial saliva
solution used as artificial saliva [70]. A minimum volume to surface area of specimen
exposed of 0.22mm2/mL was also ensured to nullify effects of oversaturation, according to
the ASTM-G31-72 [71]. A magnetic stirrer, calibrated at a rotation speed of 60rpm, was
placed at the bottom of the conical flasks to prevent limiting effects of concentration
polarization of the cathodic hydrogen evolution. Pure magnesium and PCL coated samples
were suspended in separate solutions in conical flasks via threads. The pH of the solution
was first recorded at 7.36 and the pH of the solutions containing various samples were
periodically recorded and replaced over the 2 weeks of the immersion tests. Specimens
were air dried before recording of weight.
150%
9
Passivation Zone
8
Weight Gain (%wt)
50%
6
5
4
pH- PCL Coated Mg
Clips
0%
0
2
4
6
8
10
12
14
3
16
2
pH value of solution
7
Average Weight Gain of
Magnesium Clips
Average Weight of PCL
Coated Clips
pH- Mg clips
100%
1
0
-50%
Corrosion Time (Days)
Figure 12 - The weight gain of specimens (%wt) and pH of m-PBS plotted as functions of corrosion time.
The normalized weight gain of the specimens and pH of the m-PBS is shown in
Figure 12. The uncoated magnesium strips experienced an initial increase in weight during
the first day but started decreasing thereafter, stabilizing at 50% weight loss by the first
23
week. The PCL coated strips continued to experience a large increase in weight up till the
third day, only decrease to approximately 10% weight loss at the end of the experiment.
3.3.2. Ex-vivo study
Garrett et al. [33] compared vocal fold structure across human and animal models,
concluding that dog vocal folds were the most suitable for studies on vocal fold surgery. In a
similar study, Jiang et al. [72] concluded that pigs models provided the most similarity in
vocal fold stiffness and was a reasonable alternative for phonation studies. As pigs are a
common livestock, the high availability of pig larynges from local abattoirs poses less of an
ethical concern for sacrificing animals for research purposes. Experimental evaluation of the
micro-clips was thus performed with a porcine model to evaluate the prototype’s ease of
application using microlaryngeal instrumentation, and to determine if its attachment to the
mucosa was secure.
Ex- vivo experimental evaluation of the micro-clip was performed using a cadaveric
porcine model to assess the ease of application using micro-laryngeal instrumentation, and
to determine if its attachment to the mucosa was secure. A modified micro-laryngoscopy
setup was used consisting of a standard adult laryngoscope (Promed 222mm operating
laryngoscope, Tuttlingen, Germany), custom suspension frame and operating microscope
(Zeiss OPMI, Oberkochen, Germany). Excised larynges were mounted on a frame, with the
laryngoscope inserted at its opening and oriented at an angle simulating an actual surgical
procedure. A binocular operating microscope with a 400mm lens was used to visualize the
vocal cords through the laryngoscope. A longitudinal incision was made on one or both vocal
cords using a sickle knife, creating an epithelial flap which was elevated using micro-forceps
and a dissector. The micro-clips were loaded with its distal ends facing forward, inserted
24
through the laryngoscope and orientated via the operating microscope. Once the location of
deployment was decided, the forceps was pressed down against the incision and clamped
close. Each larynx had 3-5 micro-clips implanted per larynx depending on space restrictions.
The ability of the clip to hold securely was assessed by subjecting the applied microclips to manual tensioning as well as vibration. To assess the effect of vibration, the
cadaveric larynx was secured to a frame (Figure 13) and the vocal folds were apposed to
simulate vocal fold adduction during phonation. Air was then pumped from below at 4 PSI,
through the trachea to simulate sub-glottic air pressure and induce vibration in the vocal
folds. The ability of the clips to hold securely with sustained traction or vibration was
assessed.
Figure 13 - Mounted trachea on ex-vivo setup
The ex-vivo micro-clip application procedure was carried out by a surgeon
experienced in laryngeal microsurgery techniques. Based on his feedback, the application of
the clip was found both to be significantly easier and less time consuming as compared to
25
his experience in suturing in human patients. Using the cupped forceps each clip could be
applied easily within a few seconds, with a consistent shape achieved after application.
The excised larynges were dissected and the positioning and security of the microclips was examined. Figure 14 below shows the applied micro-clips embedded in the vocal
fold. All micro-clips were found to have penetrated the epithelial layer and held the edges of
the micro-flap together securely. Tensioning of the clip resulted in considerable tenting of
the mucosa, until either the clip detached or the mucosa tore. Conversely, removal of the
implanted micro-clips was found to be difficult and required distraction of the two ends
using two pairs of forceps concurrently. A custom extractor for the clips may facilitate
removal in the event of an error in application. In the experimental setup where the vocal
folds in an excised larynx were subjected to vibration, the clips held securely despite
sustained vibration for 15 minutes.
Figure 14 – Ex-vivo experiment with excised larynx. (Left) Applied micro-clips within larynx. (Right) Tensioning
of micro-clips exhibiting their security.
3.3.3. In-vivo study
Results from in-vitro experiments may differ greatly from that of in-vivo experiments.
Witte et al. highlighted the large difference between in-vitro and in-vivo ASTM standards
26
(ASTM-D1141-98) by comparing degradation in synthetic seawater and phosphate-borate
buffer with in-vivo results [73]. The paper reported that the in-vitro corrosion rates were
approximately 4 orders of magnitude larger than that in-vivo, concluding that the current
standard in in-vitro corrosion studies may not provide adequate prediction of corrosion
rates in-vivo. Mueller et al. explored the influence of electrolyte composition in-vitro [74],
concluding that the concentration of chloride and organic molecules like proteins heavily
affects corrosion results.
By investigating the biocompatibility of our micro-clips in-vivo, we hoped to study
their bio-absorpability, correlating it with our in-vitro and ex-vivo results. In the in-vivo
studies, a similar setup to our ex-vivo studies was used. To simulate endoscopic laryngeal
microsurgery, pigs were anesthetised and positioned supine with the cervical spine slightly
flexed. The laryngoscope was inserted trans-orally and suspended on a custom made frame
that enabled adjustments to be made to the position of the scope’s tip, so as to optimize
visualization of the vocal folds. By combining this with a similar 400mm focal-length
binocular microscope used in the ex-vivo experiment, the setup was close to that expected
during surgery in an adult human as seen in Figure 15. A longitudinal incision was made on
one or both vocal folds using a sickle knife. An epithelial flap was elevated using microforceps and a dissector. The flap was then replaced and secured with either micro-clips (3-6
clips on one side), micro-suture or fibrin glue.
27
Figure 15 - In-vivo setup
All methods were carried out in a humane and ethical manner, in accordance with
guidelines set by the National Advisory Committee for Laboratory Animal Research (NACLAR).
Animal use protocol (045/08) was approved by the Institutional Animal Care and Use
Committee (IACUC), National University of Singapore (NUS). Animals were housed in the
animal holding unit at Department of Comparative Medicine (NUS) for the entire duration of
the experiment and were fed according to standard animal-care protocols.
Due to variations in size and access to the vocal fold, the number of micro-clips
implanted varied between subjects. Assuming each micro-clip experiences bio-absorption
independently, we compared three different clip modifications: unpolished magnesium,
polished magnesium and PCL coated magnesium while varying the thickness of the clips
between 0.35mm, 0.25mm and 0.2mm. The details and results are summarized in Table 1.
28
Table 1 – Summary of In-vivo Experimental Results
Pig
no.
1
2
3
Items placed on vocal fold
Ipsilateral
Contralateral
4 clips
4 clips
1 Nonabsorbable
suture
3 clips
1 absorbable
suture
Duration
Results after sacrifice
Ipsilateral
Contralateral
Remarks
2 weeks
1 clip found
0 clips found
Left
untouched
2 weeks
4 clips found
1 Nonabsorbable
suture found
0.35mm thick,
Unpolished
NA
0.35mm thick,
Polished
Left
untouched
3 weeks
2 clips found
NA
0.25 mm thick,
Polished
4 clips
4
3 clips
5 clips
3 weeks
0 clips found
1 clip found
5
4 clips
Flap redraped
3 weeks
1 clip found
NA
0.2 mm thick,
Polished
0.2 mm thick,
Polished, PCL Coated
The first pig was used primarily to investigate the rate of absorption of magnesium
as our choice material. In pigs 2 and 3, the micro-clips were implanted on one side of the
vocal folds over a created micro-flap, leaving the contra-lateral vocal fold intact so as to
investigate any adverse effects from the micro-clips. Pigs 2 and 3 also had sutures (7-0
prolene and 6-0 vicryl) placed in lieu of one of the clips, so as to compare healing results
between techniques. The thicknesses of the micro-clips were also varied between pigs 2, 3
and 4 to investigate its effects on the rate of absorption. PCL coated micro-clips were
implanted in Pig 5 and it was also utilized as a control by leaving the contra-lateral microflap
unclosed so as to compare the healing results with an un-approximated micro-flap. The pigs
were sacrificed 2-3 weeks post-surgery and their excised larynxes were fixed in 4%
formaldehyde before histological examination was carried out. Figure 16 shows the
microscopic view of the applied clips in the 3rd experiment.
29
Figure 16 – Microscopic view of the micro-clips after application in-vivo.
Feedback on the surgical procedure from the surgeon for the micro-clips was
generally positive. Implantation time was found to be less than a minute per micro-clip due
to the straightforward nature of the application technique. Due to the limited workspace
within the laryngoscope, micro-suturing was found to be more complex than applying the
microclips, requiring approximately 15 minutes per suture to complete. While the efficiency
of any procedure is dependent on experience and practice, the learning curve for microsuturing is still much steeper as compared to the micro-clips, which greatly simplified
approximation of the vocal fold wound edges, resulting in relatively large time savings per
micro-clip implantation.
From visual inspection of the excised vocal folds after sacrificing the 2nd and 3rd pigs,
there was no damage found on the contra-lateral vocal fold. Nevertheless, all excised vocal
folds were sent for histological evaluation. Figure 17 presents histological stains of the vocal
folds. In all pigs, significant numbers of neutrophils were identified around the region of clip
implantation. Neutrophils were also present when sutures were placed instead of clips, but a
slightly larger degree of inflammatory response was found from the clip implant sites. Both
macroscopic and histological examination showed no evidence of injury due to collision or
30
reaction in the contra-lateral vocal fold in the pigs undergoing unilateral vocal fold clip
insertion. Significant multinucleated giant cells and collagen was observed in the vicinity of
pure magnesium that had not been polished. This was unfavourable in healing and could
correlate to poorer phonation outcomes due to the stiffer collagen bundles that dampen
vocal fold oscillations. Healing outcomes were much improved in the 3rd and 4th pig which
had finer, polished micro-clips implanted. In the 5th porcine model, we compared the effects
of wound closure and healing of PCL coated magnesium clips. Only one of the PCL coated
magnesium clips remained in situ after three weeks and was removed during histology.
Relatively smaller numbers of neutrophils were observed surrounding the site of implant,
which may have been a result of the PCL coating on the clip reducing the degree of
inflammation.
Figure 17 – Histological results showing inflammatory reaction to the micro-clips. (Left) Un-polished
magnesium micro -clips. (Right) PCL coated micro-clips.
31
3.4. Discussion
3.4.1. Bioabsorption and biocompatibility of magnesium for the microclip
As noted earlier, magnesium degrades quickly in biological environments, especially
in well-vascularized regions of the body. However a number of factors can influence the rate
of degradation including the mass of the implant, its surface characteristics, and the nature
of the biological environment. Heublein et al. [75] estimated that total bio-corrosion of
magnesium alloy tube stents (wall thickness between 150–200 µm, length 10mm, diameter
2.5-3.5mm, weight 4 mg) occurs within 89.4 days. Zartner et al. [76] reported the
implantation of a magnesium stent (length 10mm, diameter 3mm) in a preterm baby, which
degraded fully within five months. While these degradation rates exceed our required
duration for the micro-clip, the average weight of our implant (0.66 mg) is significantly
smaller than the stents described. Our in-vitro experiments also suggest that the desired
degradation rates are achievable.
Based on the results in Table 1, surface modification of the clips has a larger effect
on the bio-absorption rate of the micro-clips than the thickness of the micro-clips. In the first
experiment, only one unpolished micro-clips was found remaining, compared to the 4
polished micro-clips inserted in the 2nd pig which persisted until its sacrifice at the end of 2
weeks. This could have been due to the larger pitting susceptibility and higher corrosion
currents of higher surface roughness [77]. The persisting polished micro-clips from the 2nd
pig however demonstrates that it was possible for the micro-clips to remain securely
attached to the vocal fold for more than 2 weeks, even though it is desirable that the microclips bio-absorb between 1 and 2 weeks after application. The large difference in results
32
from reducing the thickness of micro-clip from 0.25mm to 0.2mm in the 3rd and 4th pig
indicates that a thickness between these two values may potentially suit our requirements.
It has been shown that a high pH level of 9.23 severely reduces the survivability of
cells [78, 79]. From the histological findings in the 5th pig, the reduced scarring could be due
to a reduced inflammatory response, as the PCL coated micro-clips provide pH stability to
the implant’s environment. Despite our in-vitro finding of slower degradation of PCL coated
magnesium strips, the presence of entrapped pockets of hydrogen gas might have led to
embrittlement of the structure through the mechanisms of stress corrosion cracking which
may explain the similar rate of degradation in the 5th pig compared to the 4th pig.
Accumulation of hydrogen gas as a by-product of corrosion is a limitation to using
magnesium in certain biological situations such as for orthopedic implants, where formation
of gas pockets may need to be drained [52, 80]. However due to the surface-application
nature of the clips on the vocal folds, hydrogen gas can escape freely through the respiratory
tract and does not pose a problem in our situation. Likewise for vascular stents,
accumulation of hydrogen does not appear to pose a problem. Waksman et al. [81] studied
the degradation of magnesium alloy stents in porcine models, over a period of 3 months,
reporting the safety of using magnesium stents with no side effects.
There are also limitations in both the in-vitro and in-vivo studies that were carried
out. The in-vitro studies focused on pure magnesium specimens, comparing the effect of
surface modification on the degradation. However as replicating the environment of the
vocal fold is challenging, more popularly used electrolytes in degradation studies like Hanks’
Balanced Salt solution may be more applicable. There also exist many various alloys of
magnesium that have been reported to increase biocompatibility or modify degradation
33
speeds that were not studied in this thesis. Also, due to the low number of animals used in
the in-vivo study, the micro-clips were monitored only at the beginning and end. In-vivo
monitoring of the micro-clips over the entire length of degradation would require a much
larger sample size, with different end points for each group. Much work needs to be done to
characterize and control the rate of degradation of the micro-clips, in order to further
optimize the micro-clip for use.
Nevertheless, based on the overall histology findings from the in-vivo studies, the
lack of significant adverse tissue reactions to both the clips and the opposing untouched
vocal fold highlights its good biocompatibility and suitability of size and shape.
3.4.2. Recommendation for future work
In order to further simplify and speed up the application process, a custom
applicator was also designed to insert and compress the micro clip in order to secure the
epithelial flaps. Figure 18 below shows the designed applicator and its magnified tip.
Figure 18 – Applicator design.
34
Due to the limited view of the surgical field and the rigidity of the surgical setup,
depth perception within the laryngoscope is challenging. The applicator is thus designed to
be able to deform the micro-clip while pushing it forward, ensuring proper deployment of
the micro-clip. The addition of a rotary knob at the applicator handle can be used to rotate
and lock the orientation of applicator tip, providing the surgeon with an additional mode of
control over the tip orientation.
Currently the applicator neck diameter is approximately 5 mm, which is considerably
larger when compared to typical micro-laryngeal instruments with a neck diameter of less
than 2mm. While it obstructs a considerable amount of the view within laryngoscope,
reductions in its size can still be made by reducing the actuation shaft’s size. The applicator
tip can also be reduced by making one side rigid while actuating the other. Based on clinical
feedback, an additional yaw or pitching of the tool head needs to be included as sometimes
clip deployment needs to be carried out at an angle. Further work can be done to further
optimize the applicator and provide a complete system for deployment of the micro-clip.
35
4. Device for TEP and voice prosthesis insertion
This chapter will focus on the design, implementation and evaluation of a device for
TEP and voice prosthesis insertion. First, the design requirements are established and
proposed solution is presented in Section 4.1. The implementation of the propose solution
and its various embodiments are then presented in Section 4.2. Experimental evaluation of
the device is then carried out in Section 4.3, concluding with the discussion of the feasibility
of the prototype device in Section 4.4.
4.1. Design requirements and proposed solution
As discussed in the background and literature review, one shortcoming common to
the in-office techniques is that voice prosthesis is usually not inserted at the time of fistula
tract creation. This is firstly due to the difficulty of measuring the exact length of the
prosthesis required at the time of tract creation. Secondly, if the tract has been created
traumatically or by incising tissue, it requires time to heal. As a result, patients often are
subjected to the uncomfortable stenting of their fistula and their voice restoration process is
delayed. There is thus a need to design a device to allow for 1) immediate measurement and
2) insertion of a voice prosthesis at the time of TEP.
Inappropriate sizing of the voice prosthesis is of concern as it can lead to leakages or
complains from patients of irritation and obstruction [82]. While sophisticated medical
imaging solutions like ultrasound, x-rays and CT scans are often available in hospitals,
scheduling their use just to measure the length of the fistula may not be a feasible choice as
they may require patient movement after the initial TEP procedure. Portable versions of
these imaging devices may be more suitable, but the methods of acquiring and
36
reconstructing 3D images to identify and measure the length of the fistula are
computationally intensive and may extend the entire length of the procedure. A less
technologically complex method like introducing a physical measurement scale within the
tract may suffice.
The inspiration for immediate prosthesis insertion is drawn from the use of trocars
in surgery. Trocars are common instruments often used to drain fluid from the human body
or to create surgical ports for laproscopic surgery. These trocars are usually inserted through
hollow cannula and introduced into the body. The trocars are then removed, leaving the
cannula to maintain the opening for access. Hence for our application, we propose the
integration of a measurement scale together with a cannula for prosthesis insertion to be
used with the method reported by Lau et al. [25]. The next section details the various
embodiments of this solution.
4.2. Designs
An initial device based on adapting current tools used in [25] was first created. A
handheld device based on replacing the need for the tools used in [25] was also developed,
with an additional serial robotic manipulator capable of positioning and orientating the
handheld device.
4.2.1. Initial design
As the device design was to be built around existing equipment, the voice
prostheses to be inserted were investigated. Provox and Blom-Singer are two brands of
voice prostheses utilized in Singapore General Hospital (SGH) for voice restoration. Both
brands provide indwelling and non-indwelling voice prostheses. Indwelling prostheses have
37
been reported to provide a long-term solution, with a lengthier lifetime before requiring
change by clinicians [82]. On the other hand, non-indwelling prostheses can be easily
removed for cleaning and replaced by patients themselves. As many external factors like
inappropriate sizing or patient diet may affect the lifetime of the prosthesis, feedback from
speech therapist in SGH report that non-indwelling prosthesis are often recommended to
patients instead, due to their relatively cheaper pricing and ease of use. Non-indwelling
prostheses will be focused on for insertion in this work.
Figure 19 – Non-indwelling voice prostheses from (Left) Provox NID [83] (Right) Blom-Singer.
Non-indwelling prostheses from both brands have an external shape that is
relatively similar (Figure 19). The presence of flanges at both ends of the voice prosthesis
engages both the anterior oesophageal wall and posterior tracheal wall, keeping it in place
within the created fistula. The prostheses also come in various flange sizes (16 or 20 Fr.) and
the length (6 to 28mm). The cannula thus has to be able to fit onto the dilators from the
tracheostomy kit and yet al.low the selected prosthesis to be delivered through its body.
Based on these considerations, a prototype design is shown in Figure 20. The
prototype consists of two metal cannulae, an inner adaptor cannula and an outer
measurement cannula, that fit over the short dilator found in the short dilator used in
Portex’s minitracheostomy kit. As the smallest inner diameter to accommodate a 16 Fr voice
prosthesis (approximately 6.5mm) is larger than the widest dilator in the mini-tracheostomy
38
kit (approximately 5.3mm), an adaptor cannula was created to bridge the gap between
dilator and measurement cannula. The adaptor cannula has two advantages: First, with its
chamfered end, it allows smooth transition between the dilator and measurement cannula,
avoiding a step. Second, it enables the overlying measurement cannula to slide off more
easily compared to if the measurement cannula was directly on the dilator.
Figure 20 – Initial design. (Left) CAD drawing of 1) the measurement cannula and 2) its adaptor cannula. (Right)
Fabricated prototype used to test solution concept.
Similar to the in-office TEP procedure described earlier, puncture and prosthesis
insertion with the new device is carried out under TNE control. The device is mounted on
short dilator and is inserted after the serial curved dilators, dilating the tract further. Once in
place, the measurement cannula is left behind, and the inner adaptor cannula is removed.
External markings on the measurement cannula are visualised within the esophageal lumen
(using TNE) allowing the appropriate prosthesis length to be determined. The selected
prosthesis is then inserted directly through the cannula. Figure 21 shows the fabricated
prototype device with markings on its surface in divisions of 2mm.
A more complete version of this device was designed after preliminary tests found
that there was a need to develop a handle to aid in the insertion of the voice prosthesis.
Figure 21 shows the finalized design, which consists of an additional handle, a plunger and a
voice prosthesis loader. The handle provides grooves in which the wings of the modified
measurement and adaptor cannula can be mounted, to provide the necessary strength to
39
push the dilator through the fistula. The plunger is designed to allow controlled introduction
of the voice prosthesis through the measurement cannula and has a blunt end to avoid
damaging the voice prosthesis. Once the intra-luminal flange unfolds in the esophageal
lumen and is brought back flush with the esophageal mucosa, the measurement cannula
can be withdrawn over the prosthesis, which is kept relatively immobile by pressure from
the plunger. This push pull motion ensures that the flanges open at either end of the
tracheo-esophageal fistula and not within it. The loader helps to guide the prosthesis into
the measurement cannula and ensure the proper deformation of the flanges, so that they
unfold properly when pushed through the measurement cannula. This finalized design was
fabricated and tested in-vivo.
Figure 21 – The finalized design. From left to right, the modified measurement cannula, handle, loader and
plunger.
4.2.2. Handheld device
In addition to the initial design, a handheld device which could electromechanically
carry out the TEP procedure and insertion was also explored. As TEP and prosthesis insertion
40
share the same path, a single axis mechanism with interchangeable tools could be designed
to carry out both operations. The current version is presented in this section.
Figure 22 illustrates the design of the handheld device, consisting of a main body,
puncture tool and insertion tool driven by a rack and pinion actuator. The main body of the
device has a 3-tiered channel in which either the puncture tool or insertion tool is loaded
into the top most tool channel. The tool channel also acts like a guide, limiting motion in a
single axis, and preventing the tool from overextending through the plastic front cannula.
The top rear portion of the tool channel can be lifted for tool loading. The middle tier within
the main body allows the actuation mechanism to travel freely while the bottommost tier
houses the retraction mechanism for the measurement cannula.
Figure 22 – 3D CAD drawing of the handheld device.
The rack and pinion actuation mechanism consists of a dc motor with an encoder
that is used to actuate the loaded tool that is placed within the tool channel. The loaded tool
is attached to the actuator with an interface that allows quick interchanging of tools and
contains a force sensor that measures the tool-tissue interaction. Similar to the initial design,
the measurement cannula is a 0.5mm thick hollow tube that is engraved externally with
markers spaced at 2mm intervals. Its inner diameter of 6.5mm is large enough for a standard
41
sized voice prosthesis (16Fr, Blom-Singer) to be slid through. The measurement cannula is
engaged during the forward actuation of both puncture and insertion process.
The plastic front cannula is designed to allow the engravings on the measurement
cannula to be seen, allowing the depth in which the measurement cannula has been
inserted to be seen from outside. It also serves to allow the posterior tracheal wall to be
palpitated so that the puncture location can be confirmed through TNE.
Hurd et al. found that conical tips separates the tissue with little damage and results
in reduced bleeding [84]. Thus a 25° conical tipped trocar (shaft diameter 6.5mm) was used
as the puncture tool. It is designed to engage the measurement cannula during its forward
actuation, puncturing and carrying the measurement cannula into the fistula. Alternatively,
the tool can be modified to house a needle tip that is used for the initial puncture in TNE
guided TEP.
Similar to the plunger design in the previous section, the insertion tool is used to
introduce the voice prosthesis through the measurement cannula and into the fistula tract.
The insertion tool has a blunt end to avoid damaging the voice prosthesis and its lower half
is designed to engage the retraction mechanism on the forward stroke of the actuator.
4.2.2.1. Puncturing system
The loaded puncture tool within the measurement cannula is shown in Figure 23a.
During the forward stroke of the puncture process, the puncture tool and measurement
cannula is propelled through the plastic front cannula, penetrating the posterior tracheal
wall and anterior esophageal wall, creating the tracheoesphageal fistula Figure 23b. During
42
the retraction stroke, the measurement cannula is left within the fistula while the puncture
tool is removed for replacement with the insertion tool Figure 23c.
a
b
c
Figure 23 – (a) Loaded puncture tool before puncture. (b) Loaded puncture tool after the puncture stroke. (c)
Measurement cannula after retraction stroke. Main body is concealed for better view.
Voice prosthesis length is selected based on the width of the tracheo-esophageal
dividing wall. As the motor encoder provides position data, measurement can be performed
by subtracting the insertion depth from the marking seen with TNE within the oesphagus.
Alternatively, in event of slippage, the external and intra-luminal markings of the
measurement cannula can also be visualized to obtain the appropriate length manually,
similar to the method described for the initial manual design.
4.2.2.2. Voice prosthesis insertion system
When an appropriate voice prosthesis is selected, it is loaded on the insertion tool
and placed in the tool channel. A single forward stroke pushes the voice prosthesis into
place. Simultaneously, the lower half of the insertion tool pushes against the retraction
mechanism. The force is transferred along the flexible tubing within the U-channel, pushing
43
against the measurement cannula, in the opposite direction of the insertion tool. Figure 24
illustrates the process just before and after insertion respectively.
Figure 24– Loaded insertion tool with measurement cannula (a) just before voice prosthesis insertion. (b) after
the insertion stroke.
The insertion stroke thus results in the removal of the measurement cannula from
the fistula while pushing the prosthesis into place, allowing the prosthesis flanges to expand
and engage the anterior oesophageal and posterior tracheal wall.
4.2.2.3. Implementation
The handheld device automates the surgical procedure and its overall operation
process is outlined below:
1.
Load puncture tool, securing with interface attachment.
2.
Use tip of puncture tool to palpitate posterior tracheal wall for confirmation of the
puncture site through TNE.
3.
Activate trigger for puncture and wait for retraction.
4.
Disconnect puncture tool and remove tool while maintaining measurement cannula
within fistula.
5.
Discern length of fistula.
6.
Load selected voice prosthesis on insertion tool and secure insertion tool to actuator.
7.
Activate trigger for prosthesis insertion.
44
8.
Remove handheld device.
A modified version of the proposed design was fabricated to evaluate the feasibility
of the voice prosthesis insertion system in-vivo. To simplify actuation, a pneumatic actuator
(CDJ2B6-60R-B, SMC) was utilized instead to drive the tool with a fixed insertion depth. The
fabricated main body of the system with the puncture and insertion tools is shown in Figure
25 respectively.
Figure 25 – Fabricated main body of the handheld device with the measurement cannula and puncture tool. (Left) After the
puncture stroke. (Right) After the insertion stroke.
4.2.3. Manipulator system
In addition to the handheld device, a robotic manipulator system was also designed
to aid in its orientation and positioning. Based on a macro-micro positioning concept, the
manipulator is illustrated in Figure 26 below.
45
Figure 26 - 3D CAD drawing of manipulator system with handheld device mounted.
The manipulator is an 8 degree of freedom (DOF) serial manipulator consisting of 3
passive links and 5 motorized axles, and can be mounted on the side rail of a standard
surgical bed. The 3 passive joints in R-P-R configuration are responsible for the initial macro
positioning of the manipulator. The 5 DOF (P-P-R-R-P configuration) sub-manipulator system
located at the distal end provides the final micro positioning and orientation of its end
effector.
4.2.3.1. Forward Kinematics
Figure 27 - Frame assignment for the manipulator with an alternate end effector for gripping a trocar.
46
In order to be able to define the position of the end effector, a kinematic model is
established. Figure 27 depicts the assignment of frames to the serial manipulator based on
the Denavit Hartenberg convention described by Fu [85] in order to generate the
transformation matrix of the system.
Table 2 ̶ DH parameters for the manipulator
Link Parameters
3
4
5
6
7
θ
90
90
q6
q7
0
d
q4
d5+q5
0
d7
d8+q8
a
0
a5
0
0
a8
α
90
0
-90
90
0
Table 2 displays the joint variables and link parameters of the manipulator system
obtained based on the frame assignment. Hence the kinematic equation of the manipulator
is represented in the transformation matrix as shown in (1). Detailed calculation of the
forward kinematics is shown in the Appendix.
𝑑5 + 𝑞5 + (d8 + q8)cos 𝑞7 − 𝑎8 sin 𝑞7
𝑥
−𝑑7 cos 𝑞6 − (d8 + q8)sin 𝑞6 sin 𝑞7 − 𝑎8 cos 𝑞7 sin 𝑞6
�𝑦� = �
�
𝑧
𝑎5 + 𝑞4 − 𝑑7 sin 𝑞6 + (d8 + q8)cos 𝑞6 sin 𝑞7 + 𝑎8 cos 𝑞6 cos 𝑞7
(1)
4.2.3.2. Hardware Implementation
The fabricated submanipulator is shown below in Figure 28. High precision
translational stages (Ezlimo, Oriental Motors) are used for joints 3 and 4, with positioning
accuracy of 0.02mm. Two stepper motors (ARseries, Oriental Motors) provide the actuation
for joints 5 and 6, with positioning accuracy of 0.018˚/pulse. Due to the high accuracy of the
hardware, open loop control was found to be suitable for the requirements. The
manipulator system is approximately 48cm long, 28cm wide and 28 cm in height.
47
Figure 28 – Fabricated manipulator system for handheld device
4.2.3.3. Software and operation interface
The software for motion control was developed in Labview’s graphical programming
environment. Two modes of operation were developed – teleoperation and predefined. In
teleoperation mode, each individual joint of the sub-manipulator is controlled manually by
the operator. In predefined mode, the operator is able to key in a predefined distance or
angle before commanding the manipulator to move, allowing minute and controlled
adjustments to be carried out. Figure 29 shows the visual interface of the system in both
teleoperation and pre-defined mode.
Figure 29 – User interface of manipulator system. (Left) Teleoperation mode and (Right) predefined mode.
48
Using a National InstrumentTM M series multifunction DAQ module (USB-6221), the
control signals to the motor drivers are generated in the form of 5V TTL pulse trains. In
addition to the software interface, a simulated environment was developed in Matlab to
monitor the positioning of the system (Figure 30). Based on the inputs of the operator, the
final position of the end efffector can be estimated and viewed in the environment.
Figure 30 – Simulated environment. (Left) Matlab simulation of the configuration of the manipulator. (Right)
Sub-manipulator mounted with an earlier version of the handheld device
49
4.3. Experiments and results
The devices were tested in-vivo to investigate their feasibility. Due to its similarity
with human larynx dimensions [72, 86], a porcine model was used for experimentation. In
order to mimic an actual surgical procedure, the pig’s neck tissue had to be dissected to
expose the trachea. A section of the anterior tracheal wall was removed and its edges were
sutured to created a simulated tracheostome (Figure 31). Similar to a typical in-office
procedure, a TNE system was then inserted for visualization of the insertion site within the
esophagus before TEP was carried out
Figure 31 – In-vivo experiment. (Left) Simulated tracheostome. (Right) TNE system.
All methods were carried out in a humane and ethical manner, in accordance with
guidelines set by the National Advisory Committee for Laboratory Animal Research (NACLAR).
Animal use protocol (018/09) was approved by the Institutional Animal Care and Use
Committee (IACUC), National University of Singapore (NUS).
4.3.1. Manual device
The initial manual device was first tested to evaluate the feasibility of the design
concept.
50
A
B
C
D
E
F
G
H
Figure 32 - Experimental evaluation of the manual device. (A) Palpitation of anterior tracheal wall. (B) Initial
puncture with needle. (C) Guide wire insertion. (D) Removal of needle. (E) Insertion of dilator with manual
device. (F) Insertion of prosthesis after remove of dilator. (G) Removal of measurement cannula. (H) External
view of the surgical site.
Figure 32 depicts the various stages from TEP creation to voice prosthesis insertion.
First, the posterior tracheal wall was first palpitated to confirm the location of the initial
puncture (A). A 14g needle was then used for the initial stab puncture(B). Some slight
51
trauma was inflicted on the posterior oesophagus wall. Next, the guide wire was inserted
through the needle (C) and the needle was removed (D). The measurement cannula
together with the adaptor cannula and the short dilator was then inserted with the
assistance of the guide wire (E). The dilator and the adaptor cannula were removed and a
voice prosthesis (16 Fr, 8mm length) was inserted with the help of the plunger (F). Finally the
measurement cannula was removed (G) and the prosthesis was found to fit snugly in place
(H). The entire procedure was found to take less than 30 minutes, with feedback from the
surgeon that using device was not difficult and could be integrated into the current
procedure without extensive training.
4.3.2. Handheld device
The voice prosthesis insertion system for the handheld device was also tested invivo. A duckbill voice prosthesis (16Fr, 10mm length, Blom-Singer) was chosen and inserted.
Figure 33b depicts the inserted duckbill voice prosthesis, which was found to fit tightly.
Figure 33– Handheld device used to Inserted the voice prosthesis within the fistula. (Left) Measurement cannula within
fistula. (Right) Inserted duckbill voice prosthesis.
While only the voice prosthesis insertion system was tested, it was noted that the
voice prosthesis insertion process had a large amount of recoil. This is undesirable during the
52
puncture process, as it can lead to erroneous positioning and fistula creation. This may be
mitigated by the use of a robotic manipulator arm designed in Section 4.2.3 which is stiffer
and more stable than a human arm.
4.4. Discussion
The results of the in-vivo evaluation of the device have shown the potential of this
relatively simple but effectively solution to the limitation in current procedures. Another
advantage of the cannula concept is that as the size of the fistula is dependent on the
cannula that is used for dilation, a standardized flange size can be chosen for implantation.
Although fistulas tend to shrink spontaneously [63], one of the primary complications after
voice prosthesis insertion is still leakage. Usually the result of a poor choice in prosthesis size,
the same device can be used to re-dilate the fistula and inserted a newer and more suitable
prosthesis.
As discussed in the earlier section 4.2.1, the device was specifically designed to
accommodate a 16Fr non-indwelling voice prosthesis from Blom-singer. With the large
variation in voice prostheses type and dimensions available in the market, the serial
cannulae will need to be designed around the size of the prosthesis if other brands or
versions of voice prostheses are to be used. Nevertheless, the device will work with all
length variations of the 16Fr voice prosthesis.
4.4.1. Recommendations and future work
While a large amount of work has been done to evaluate the cannulation for
insertion of the voice prosthesis, there remains some improvements that can be
implemented in the handheld device. Currently, the handheld device is pneumatically
53
actuated and does not have a feedback system. A possible schematic diagram of the
handheld is illustrated in Figure 34.
Force sensor
Force
Encoder
Amplifier
/filter
Computer
Stoma
Trachea
Motor Driver
Esophagus
Figure 34 – Schematic diagram of the handheld device.
Due to the viscoelastic properties of soft tissue, tissue deformation can be reduced
by increasing puncture velocity [87]. This is of particular interest to us as the diameter of the
esophageal lumen is between 15 and 20mm [88]. In order to minimize trauma to the
posterior esophageal wall, the puncture tool needs to be halted and retracted before
puncturing the anterior esophageal wall.
Force data from the force sensor within the tool actuation mechanism can be used
to identify the puncture event. Due to the lack of data in the literature specifying the range
of force required for the creation of a tracheoesophageal fistula, a preliminary in-vivo
experiment on a porcine model was carried out to provide an estimation of the
requirements. A force sensor (Nano17, ATI) was attached to a 14g needle and was inserted
at 2mm/s at 5 locations along the posterior tracheal wall of a pig. Figure 35 shows the plot of
the force. The measured force at time of puncture varied from 0.1N to 0.2N, and dropped at
least 0.05N after puncture within 0.25s. This abrupt drop in force can be used to identify the
puncture event.
54
Figure 35– In-vivo force data of 14G needle insertion through posterior tracheal wall and anterior esophageal wall.
Puncture detection can thus be carried out by differentiating the force data
obtained by the force sensor. When the difference rises above a preset threshold, it is
identified as a puncture event and the actuation mechanism drives the needle in the reverse
direction to prevent overextension of the puncture tool.
Based on our preliminary in-vivo results, detection of tissue puncture in our context
has to be performed within 0.5s so that the insertion can be stopped in time, preventing
injury to the posterior tracheal wall. This window shrinks the higher the puncture velocity is
increased. Saito et al. [89] described the use of a second-order low pass filter for automatic
puncture detection, reporting a delay of less than 0.3s. However, force data obtained from
manual experiments were used in his system to optimize parameters in order to reduce
delay in the automated puncture detection. This may not be achievable in implementation
due to the increased tissue trauma and the limited space of the tracheostome.
55
Online estimation models can be used to predict puncture events. Barbe et al. [90]
utilized a recursive least squares (RLS) algorithm with covariance resetting to model the
force response of the tissue during needle insertion. Their estimation model used fault
detection principles to identify force transitions, obtaining detection results with a time
delay of approximately 30ms. In the same vein, Kasahara et al. [91] used RLS to estimate
environmental stiffness. Changes in stiffness identified by preset thresholds were used in
their puncture detection algorithm.
The described methodologies above can be adapted for the handheld device to
further enhance the safety of the puncture process. Also, as an initial palpitation of the
posterior tracheal wall is required for confirmation of the puncture site through TNE, force
data measured through this initial step could be utilized to obtain initial parameters for the
online estimation model, possibly reducing convergence time. The force required for
puncture may also be reduced with the use of a beveled tipped puncture tool [92], which
may reduce the recoil of the system.
56
5. Conclusion
In this thesis, the research and development process of two projects has been
reported. For vocal fold wound closure in voice microsurgery, novel bio-absorbable microclips have been developed. Constructed from magnesium, these C-shaped micro-clips can be
applied easily by microlaryngeal surgical forceps to reapproximate epithelial flaps of vocal
fold wounds. Experimental results from in-vivo survival studies with a pig model have shown
the potential of the clip for use as an alternate wound closure technique in vocal fold
microsurgery. Further work still needs to be carried out to optimize exact material
composition of the clip, with the possible use of coatings to enhance biocompatibility.
Customized micro-clip insertion and removal tools can further aid in its application.
Similarly for voice restoration, a device consisting of two concentric metal cannulae
have been developed. The external cannula is inscribed with a measurement scale, while the
inner cannula is used as an adaptor. Together with TNE and tools from a commercially
available tracheostomy kit, the device enables immediate sizing and insertion of a voice
prosthesis after TEP. A handheld device based on the similar cannulation concept has also
been developed which enables both TEP and prosthesis insertion within a single device. A
robotic manipulator has also been developed to carry out the TEP and voice prosthesis
insertion, providing a more stable and accurate solution. The device and its various
embodiments were also tested in-vivo to evaluate their feasibility. Experimental results
show that with the device, an appropriately sized prosthesis can be easily and quickly
inserted at the time of TEP. Immediate voice restoration is possible, with little additional
procedural time added to the current in-office procedure.
57
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62
7. Appendix I –Technical drawings
7.1. Micro-clip
63
7.2. Manual TEP device
64
65
66
67
68
7.3. Handheld TEP device
69
70
71
72
7.4. Calculation of the end effector position for the robotic manipulator
Equation 2 below is used to generate the transformation matrices between frames based on DH convention:
𝑖
𝑇𝑖−1
cos θi
sin θi
=�
0
0
−sin θi cos 𝛼𝑖
cos θi cos 𝛼𝑖
sin αi
0
sin θi sin αi
− cos θi sin αi
cos 𝛼𝑖
0
Based on the link parameters in Table 2, hence
0
1
𝑇34 = �
0
0
𝑎 cos θi
𝑎 sin θi
�
𝑑𝑖
1
(2)
0 1 0
0 0 0
�,
1 0 𝑞4
0 0 1
0 −1 0
1
0 0
𝑇45 = �
0 0 1
0 0 0
0
𝑎5
�,
𝑑5 + 𝑞5
1
cos q6 0 − sin q6 0
sin q6 0
cos q6 0
𝑇56 = �
�,
0
−1
0
0
0
0
0
1
73
𝑇67
cos q7
sin q7
=�
0
0
1
0
𝑇78 = �
0
0
0 sin q7
0
0 −cos q7 0
�,
1
0
𝑑7
0
0
1
0 0
𝑎8
1 0
0
�,
0 1 𝑑8 + 𝑞8
0 0
1
8
𝑇38 = 𝑇78 𝑇67 𝑇56 𝑇45 𝑇34 = �𝑅3
0
where
𝑅38
𝑃𝑖8
𝑃38 �,
1
− sin q7
0
cos q7
−cos
q7
sin
q6
−cos
q6
−sin
q6 sin q7�,
=�
cos q6 cos q7 − sin q6 cos q6 sin q7
𝑑5 + 𝑞5 + (d8 + q8)cos 𝑞7 − 𝑎8 sin 𝑞7
−𝑑7 cos 𝑞6 − (d8 + q8)sin 𝑞6 sin 𝑞7 − 𝑎8 cos 𝑞7 sin 𝑞6
=�
�.
𝑎5 + 𝑞4 − 𝑑7 sin 𝑞6 + (d8 + q8)cos 𝑞6 sin 𝑞7 + 𝑎8 cos 𝑞6 cos 𝑞7
74
[...]... puncture and leveraging on the visual advantages TNE provides, it is hoped that such a device allows immediate voice restoration for patients, reducing recovery time and thus translating to lower costs 1.3 Research scope and organization of thesis This study focuses on the design and development of two separate surgical devices to aid the restoration of voice in patients in both voice microsurgery and total... apposition of epithelial flaps, it is hoped that such surgical micro-clips have the potential to reduce procedure time and vocal fold scar, cumulating in better surgical outcomes and cost savings for patients 5 For voice restoration, an improvement in the current voice restoration method of voice prosthesis insertion is required By developing a device to insert the voice prosthesis immediately at the time of. .. the background of the research topic as well as the motivation and objectives of the project Chapter Two reviews the current state of the art and related topics Chapter Three presents the development of the bio-absorbable micro-clips for would closure and their evaluation in ex-vivo and in-vivo experiments Chapter Four presents the development of various versions of the device for TEP and voice prosthesis... trachea for breathing (Figure 2) Figure 2 - Before and after Laryngectomy Images courtesy of InHeath Technologies [8] which supplies BlomSinger voice prostheses There are a number of options available for voice rehabilitation, ranging from oesophageal speech, electrolaryngeal speech and prosthetic valve speech Prosthetic voice restoration provides the closest approximation to normal laryngeal voice and. .. After which, the patient returns to have a voice prosthesis sized and inserted, restoring his ability to speak 1.2 Motivation and objective Our ability to express and communicate our thoughts and ideas is one that many of us cannot afford to lose The disabling psychosocial and economic consequence of losing one’s voice is an ordeal for many patients and it is of great interest to reduce or mitigate such... - voice microsurgery and voice restoration For voice microsurgery, the main objective is to develop a small clip to be applied to close incisions on the vocal fold, with at least comparable wound holding and healing properties to current methods Based on combining the ease and efficiency of using fibrin glue with the precision and security of micro-sutures by specifically designing the micro-clip and. .. esophageal perforation, and oral injury [28] It enables cannulation of the esophagus in patients with limited neck extension or stenosis of the neopharynx [29], allows rapid recovery and decreases the need for patient monitoring Also, performing the procedure in an outpatient, office-based setting reduces patient cost A stent in the form of a nasogastric tube or catheter is often left in the fistula for one... the reduction or loss of voice capabilities In moderate cases like the growth of benign vocal fold lesions, voice microsurgery is commonly used for treatment In more severe cases like total laryngectomy, voice restoration methods are required instead 1.1.1 Voice microsurgery One of the most common causes of voice disorders are benign vocal fold lesions such as nodules, polyps and cysts While these... after removal of benign lesion and (Right) redraping of microflap The microflap technique has been accepted as the standard approach for cold surgical removal of benign vocal fold lesions [37, 39, 40], achieving the main principles of vocal fold surgery by minimal tissue excision and minimal trauma to SLLP and epithelium This technique typically involves the initial creation of an epithelial incision beside... limitation of instrument movement to 4 degrees of freedom, reduced force feedback and loss of stereopsis High level of skill is required during suturing and surgeons must exercise care not to grasp the deeper structures of the vocal folds Fleming et al [35] also identified the length of time required for suture placement as the main disadvantage of this technique, suggesting that practice and familiarization ... and thus translating to lower costs 1.3 Research scope and organization of thesis This study focuses on the design and development of two separate surgical devices to aid the restoration of voice. .. complete system for deployment of the micro-clip 35 Device for TEP and voice prosthesis insertion This chapter will focus on the design, implementation and evaluation of a device for TEP and voice prosthesis... fold scar, cumulating in better surgical outcomes and cost savings for patients For voice restoration, an improvement in the current voice restoration method of voice prosthesis insertion is required
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