1697 E.117th Street
Cleveland, Oh, 44106
Professor Eric Earnhardt
Department of English, Case Western Reserve University
Guilford House
11112 Bellflower Road
Cleveland, OH, 44106
April 18th, 2014
Dear Professor Earnhardt,
Attached you will find a proposal that I have drafted for a multidisciplinary research
project of which I plan to conduct while in the Case Western Reserve University School
of Medicine. The proposal is entitled “Mechanical and Biological Verifications of
Optimal Sternal Reconstruction Method”. As the title suggests, the proposal intends to
utilize both mechanical and biological methods to validate the efficacy of the optimal
sternal reconstruction method, which is selected based on an exhaustive literature search.
Specifically, the project will verify the material biocompatibility, material and implant
mechanical property in sequence.
The importance and relevance of the research is highlighted throughout the proposal,
based primarily on previous case studies and background research. In general, sternum
serves an important role in maintaining chest wall stability, which is critical at sustaining
the normal breathing motion. Many medical procedures and adverse health conditions
may lead to sternal resection, which effectively disrupts the chest wall stability. Thus,
proper sternal reconstruction is central in restoring chest wall stability and associated
physiological functions. The goal of this research proposal is to further our understanding
of current reconstruction method, and possibly formalize an optimal method for future
references.
The main difficulty I have had in writing this proposal has been appealing to a diverse
audience body. This project is foremost tailored to medical professionals, especially those
working with sternal resection and reconstruction. It is my intention to describe the
medical procedure and testing protocols in detail to offer a comprehensive understanding
of the topic for medical experts. On the other hand, I do believe that medical research
should be understandable by average people so he or she can properly educate him or
herself before undergoes the said procedure. Thus, a conflict of audience knowledge level
deemed the writing difficult. As a result, you can probably observe a redundancy
throughout the proposal --- it is an effort to help average reader to better comprehend the
proposal.
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In addition, I have opted to not include a picture in this proposal, other than the Gantt
chart. The reasoning is that the pictures associated with sternal reconstruction surgery are
often too explicit for most audience. Thus, I omitted the picture section.
Both Dr. Xin Yu and Dr. Zijian Xie deserve recognition for my training and previous
research opportunities. Without their selfless support, I could not have established myself
as an aspiring medical researcher.
I look forward to any and all feedback you may have of this proposal, and appreciate
your time in doing such.
Sincerely,
Xin Li
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Mechanical and Biological Verifications of Optimal Sternal
Reconstruction Method
Xin Li
Case Western Reserve University
Cleveland, Ohio 44106
Abstract
Sternal reconstruction is a highly relevant topic in the medical field. Open chest
surgeries often involve the resection of sternal matter and the surrounding ribs, which
effectively interrupts the chest cage integrity. In essence, sternum is critical in
maintaining the rib cage stability, and plays a crucial role in sustaining normal breathing
motion. Improper sternal reconstruction could lead to medical complications, most
notably the flail chest, which could cause patient mortality. However, to date, only
anecdotal evidence of sternal reconstruction has been reported in the form of case studies.
There has been a consistent lack of scientific, controlled studies of different
reconstruction methods. Given the relative importance of sternal reconstruction, it is
necessary to formalize an optimal method for both patient well-being and medical
purposes. Therefore, this study aims to comb through the existing case studies to
determine an optimal sternal reconstruction method. Furthermore, the author intends to
utilize both mechanical and biological testing to validate the efficacy of the said method.
The author would also like to request assistance in both fields due to the relative
unfamiliarity. With the support of the Case Western Reserve University community, the
author hopes to advance the research to clinical trials and long term follow-up studies.
The following pages include an overview of past and current research trend, a brief
description of methodology, a proof of researcher qualification and a timetable.
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Table of Contents
Abstract ........................................................................................................................................... 3
Project Description .......................................................................................................................... 5
Project Plan...................................................................................................................................... 6
Areas of Improvement ................................................................................................................ 6
Material Mechanical Property ................................................................................................. 6
Material Biocompatibility ........................................................................................................ 6
Surgical Methods ..................................................................................................................... 6
Controlled Research ................................................................................................................ 7
Relevance .................................................................................................................................... 7
Plan of Work ................................................................................................................................ 8
Hypothesis ............................................................................................................................... 8
Human Sternal Model ............................................................................................................. 8
Biocompatibility Test ............................................................................................................... 8
Mechanical Testing of Material Property ................................................................................ 9
Mechanical Testing of Implant Property ............................................................................... 10
Schedule of Work .......................................................................................................................... 10
Qualification of Researcher ........................................................................................................... 11
Anticipated Audience Involvement ............................................................................................... 11
Works Cited ................................................................................................................................... 12
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Project Description
This project intends to determine an optimal sternal reconstruction method from the
current case studies. In addition, mechanical and biological experiments are planned to
validate the efficacy of the proposed reconstruction method.
Sternal reconstruction is of great medical relevance. Traditionally, open heart
surgeries require sternal resection to reveal organs underneath, namely the heart and the
lungs. In addition, in the case of malignant or benign tumor metastasis, parts of the
sternum and attached ribs have to be removed to prevent further tumor development. The
resection effectively disrupts the chest wall stability. It is also widely understood that
stability is important in maintaining normal breathing motion. In essence, the lung
expands due to a negative pressure in the pleural space, which is bounded by double
membrane between the rib cage and the lungs. The integrity of such space is safeguarded
by the rigidity of the chest wall [1]. Thus, a lack of chest stability due to sternal resection
could result in medical complications, including the flail chest. The missing sternal
component causes an inward motion of the rib cage due to the pressure difference across
the chest wall. The consequence, in the worst case, is a perforated lung, which is fatal.
Patients who suffer from flail chest often complain about long term chest pain, and
motion impedance as chest wall stability is critical to upper body functions [2]. Various
case studies claim that the poor sternal reconstruction results in a 10% - 40% mortality
rate [3].
Given the relative importance of the sternal reconstruction, it is perplexing to observe
that there has not been a formalized material choice or surgical method. A myriad of
materials have been reported to manufacture the implant, including metal, ceramics,
plastics, synthetic mixture, and graft [4, 6, 7, 12]. On the other hand, a wide range of
surgical methods have been documented, including mesh, shaped implant, and graft [6-8.
13-15]. In addition, only case studies have been reported to provide anecdotal evidence of
the reconstruction efficacy. It is bewildering to see only a few scientific studies have been
conducted in relevance to sternal properties. Thus, a controlled research with proper
experimental design is required to validate the effectiveness of the current reconstruction
methods to prod for an optimal procedure.
This study is projected to be multidisciplinary. It will include both biocompatibility
and mechanical tests to examine how well the implant material can integrate with the
surrounding tissue. In addition, the author would like to request for permission to conduct
animal studies. It is anticipated that the author will request for assistance from both the
Department of Mechanical Engineering and the School of Medicine to help with
experimental setup. The study intends to explore the current reconstruction methods, and
formalize the surgical protocol by using controlled studies. The following sections
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include a brief overview of the current research shortcomings, a hypothesis based upon
the research trend, a plan of action, a time table, and author’s qualification.
Project Plan
Areas of Improvement
Material Mechanical Property
Traditionally, sternal reconstruction has been performed with implants of various
compositions. The material properties demand a balance between rigidity and
malleability --- the implant needs to be rigid enough to withstand the pressure difference
across the chest wall, and support the upper body movement. On the other hand, it needs
to be flexible enough to prevent the bone abrasion due to the difference in Young’s
modulus, which measures the relative hardness. In addition, the implant must be pliable
to conform to the shape of the chest wall [4]. Titanium offers a great balance between
rigidity and malleability, and is often buttressed with rigid plastic such as PTFE to
achieve structural stability [12]. Recently, there have been dissenting voices over
titanium. Milisavljevic et al. reported in a case study that the traditional titanium mesh
would lead to chronic pain, tissue erosion, and hematoma. In turn, they proposed a new
sternal implant composed of 75% methyl methacrylate-styrene copolymer and 25%
polymethyl-methacrylate [6]. On the other front, there have been promising reports on the
usage of autograft (transfer of partial large bony structures), which theoretically induces a
minimal immune response, and offers an excellent platform for bone regeneration [7].
Material Biocompatibility
Other than the mechanical properties, it is widely understood that the implant
biocompatibility is important in the sternal reconstruction. Biocompatibility measures
how well the cells can tolerate the presence of a foreign body, namely the implant. Poor
compatibility would lead to loose connections between implants and bony structures. In
addition, immune response ensues to further erode the tissue-implant interface [5]. There
have been various reports on the biocompatibility of the titanium implant. Interestingly,
they often offer contradicting views --- Sanchehz et al. claim that titanium is
biocompatible while Wanatabe et al. insist that titanium does not provide optimal
osteoconductivity [2, 5]. Various materials have also been tested for biocompatibility
including ceramics and polymers [5, 8]. However, the results vary.
Surgical Methods
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Apart from the apparent ambiguity on the material choice, there appears to be an
over-abundance of surgical methods. The broad categories can be summarized into mesh,
shaped implant, and graft. Mesh method has been proven to be easy to use [13]. It could
be bent or reshaped to conform to the chest wall. However, it has been reported that
improper mesh insertion could lead to insecure contact between the implant and the
underneath bony structure. The result could be chronic pain and hematoma, which is a
slow local accumulation of blood due to disrupted tissue structure [6, 14]. In response,
shaped implants are created to mimic the exact geometric shape of the missing sternal
matter. The customized system is predictably more complicated. A few commercialized
methods have been reported [7, 8]. All variations of shaped implants nonetheless involve
complex adjustable gadgets. Recently, allo- and auto-graft has been utilized sporadically.
Grafts involve transplanting bony structures from the host and animal or human donors
[7, 15]. The long term effect is yet to be determined.
Controlled Research
Aside from the technicality, the biggest problem in sternal reconstruction lies in the
lack of controlled, scientific studies. So far, case studies have been widely documented
but very few controlled studies have been conducted. Various case studies have detailed
the material selection and surgical method. Sanchez et al. reported a series of case studies
after patients suffered from malignant tumor [2]. Liu et al. also recorded in detail the
implantation of titanium plates after patients underwent en bloc sternal resection [9].
However, the lack of controlled studies makes it difficult to compare and contrast results
from two different approaches. Interestingly, there have been attempts to utilize scientific
experimental design to assess the sternal structural integrity. A report from 2010 used
mechanical testing to monitor sternal response of repeated cyclical loading, which
simulated the physical condition of the normal breathing motion [10]. Baleani et al. went
even further to test the sternal loading for sternal resection [11]. However, to date, there
have been no studies that employ controlled experimental design to examine the current
treatment options.
Relevance
In conclusion, it is clear from previous studies that there is a disconnection between
case studies and controlled research. Various case studies have documented an abundance
of treatment options and material choices. However, few rigorous studies have been
performed to compare and contrast the different treatment options. It is worth noting that
scientific, controlled studies have already been incorporated into examining the sternal
structural integrity. Thus, the time is ripe for a combination of both scientific
experimental design and traditional case studies. This study aims to sift through existing
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case studies to identify an optimal treatment option, and validate such method with
mechanical tests and a biocompatibility test.
Plan of Work
Hypothesis
From the current literature review, it is understood that titanium offers a great balance
between rigidity and malleability. Despite its potential detrimental long-term effect on
bony structure, titanium has been among the most widely used materials. On the other
hand, apart from a few reports, titanium has been generally reported to have sufficient
biocompatibility. And it is evident from the literature review that shaped implant
achieves the best long-term effect on the patient’s well-being --- it induces better bone
integration. Thus, it is hypothesized that titanium, shaped implant will provide the best
surgical outcome, and benefit the patient in the long run.
Human Sternal Model
Ideally, the study should be performed on human patients to obtain optimal data.
However, this approach is unattainable due to both ethical and economical limitations.
Thus, the author intends to adopt an alternative from previous studies. Cohen et al.
described a method to approximate the human sternum with 20 lb/ft^3 rigid polyurethane
foam. The model also includes the surrounding rib cages [16]. The ribs will be embedded
into specially designed cups using polymethylmethacrylate and secured transversely by
three cotter pins. The initial casting mold for the sternum implant will be fabricated with
3D models created in SolidWorks®, and printed on a 3D printer. The initial mold will be
replaced by a polyurethane plastic mold. The implant will then be created by filling the
mold with rigid polyurethane foam. The completed human sternal model will be
subjected to mechanical testing described in section “mechanical testing of material
property” to determine whether it closely simulates the actual human sternal specimen.
Biocompatibility Test
For the purpose of an exhaustive approach, a wide range of materials will be tested in
this section: titanium, methylmethacrylate, ceramics, Crylate (75% methyl methacrylatestyrene copolymer and 25% polymethyl-methacrylate), and lamb sterna. The selection
aims to cover the major categories in this study: metal/alloy, plastic, ceramics, synthetic
mixture, and graft. The material specimen other than sheep sterna will be reshaped into a
5 by 5 by 0.5 cm square to offer sufficient surface area for cells to lodge. Note that the
lamb sternum is obtained from freshly sacrificed animal sample, and the specimen has to
be preserved in 0 degree temperature [17]. All material specimens will be immersed in
TEP, a fixing agent, and irradiated with a ultra-violet light for 17 hours to sterilize the
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samples. The human cell strain used in this experiment will be the S HeLa cell, which is a
commonly used cell line. Consequently, the S HeLa cell is placed onto the sample
material specimen. Note that confluence should be vigorously checked prior to the
experiment by using hand-click counter. The standard for uniform confluence should be
at least 100 cells per square millimeter. The extraction procedure will be modified from
the process described by Nakamura et al. [18]. Extraction was made by immersing the
loaded cell module in MEM, a common cell culture medium, in a tightly sealed
Erlenmeyer flask for 2 weeks. The nutrition is supplied by MEM and oxygen is ensured
by the filtered air pump through Y-tubes. At the end of the 2 week period, the extraction
from the cell colony is examined to inspect the health of the cellular growth. The
relationship between the surface area of a specimen and the volume of medium for
extraction will be maintained at 1 square centimeter versus 10 ml throughout the entire in
vitro biocompatibility check-up. The total experiments will last for 20 weeks, with 10
extractions during the process. The extraction will be carried out in a gyratory shaker at
200 rpm at 37 Celsius. The dynamic extraction allows the cells to move freely in the
flask. By the end of the 20 week period, the cellular content will be sacrificed with high
concentration of trypsin, a typical cellular agent which aims to dislodge the cell from the
mounting surface. The cellular content is then fixed with 5% paraformaldehyde. The
specimen along with fixed cellular content will then by stained by Mason’s Trichrome
protocol. The cellular density will be examined by using a confocal camera to image a
circular area with radius of 17 millimeters. The number of cells within the said area is
manually counted. The same procedure will be repeated five times for each specimen to
minimize the impact of random variables. On the other hand, the histological data will be
supported by the analysis of extraction following each of the 2-week periods.
Mechanical Testing of Material Property
The same material basket will be tested for this section. The author adopts a
procedure described by M. Simon [19]. The testing subject will be bolted on a 500 mm
thick concrete foundation wall with an oil cushioning pillow in between. The method
requires sensors to be placed on the fixed considered position, and interested area. This is
particularly important in the sheep sterna testing as they assume an irregular shape
compared with the standard 5 by 5 by 0.5 centimeters square of the other testing
materials. Notice the sensor is not directly attached to the specimen in order to avoid
damage from direct impact. Instead, the sensors are connected to the specimens by a
force-transiting probe. The sensors are connected with a 12 gauge wire to the force
analyzer. The signal will be amplified with a two-stage op amp circuitry to filter the high
frequency noise. The signal will then be filtered through a band-limited filter to eliminate
the static noise due to electronics, and processed by mathematical software. The proper
software is currently still to be determined. The impact hammer is mounted on an
articulated arm from the ceiling of the room, and calibrated by keeping the same
9
polyurethane tip during tests, and a constant height. The direction of the impact test and
positions of the sensors are adjusted continuously throughout the experiment to
counteract the impact of phase shift due to the normal force produced by the hammer tip.
After the data is recorded and processed, the shock impulse and the impulse response of
the material will be thoroughly analyzed to determine the rigidity and malleability of the
given materials. In addition, the measured rigidity and malleability will be cross-checked
with the values from the Case Western engineering handbook to verify the validity of the
experiment.
Mechanical Testing of Implant Property
Upon the completion of mechanical testing for each of the candidate materials, the
author intends to proceed to test the mechanical property of the implant under
physiological condition. The human sternal model will undergo a resection from the
manubriosternal joint to the xiphoid process, which are two bony land markers in human
sternum. In addition, 2 centimeters of ribs will be sectioned on either side to reveal an
oval area of approximately 30 square centimeters. This type of sternal resection is
commonly used in case studies [1-12]. The missing sternal component is fixed with each
of the three major surgical methods: mesh, shaped implant, and graft. The mesh will be
fixed in place by using stainless steel wires to the remaining bony structure. The shaped
implant tested for this experiment is the Ley’s prosthesis, which can be fixed to the bony
remaining by pre-determined screws. The sheep sterna graft will be performed by fixing
the tissue-graft interface by titanium transverse slate. The human sternal model along
with the implant will then be subjected to cyclic loading to approximate the rib cage
movement under normal breathing motion. The cycling loading protocol is adopted from
Losanoff et al. [20]. The module is attached to a biomechanical testing device (TAHDi
Texture Analyzer; Texture Technologies Corporation, Scarsdale, NY) set for repetitive
cyclic loads of 400 and 800 N and speeds of 0.04 and 0.5 mm/s. Preliminary assessment
of the sternal failure is measured after 12 hours to examine the difference among three
surgical methods. The sternal displacement is measured, specifically at the manubrial and
xiphoid ends. In addition, the tissue-implant interface is carefully examined to prod for
potential erosion of ribs and loose connection between ribs and the implant. Note that the
simulation is an expedited process. Thus, the experiment only serves as a reference.
Schedule of Work
This research project will take approximately 6 months to complete. The author would
spend approximately one to two months doing an exhaustive literature search. Needless
to mention, the current material basket and surgical methods will be updated to reflect the
current research interest. Upon the completion of literature search, both biocompatibility
10
test and mechanical testing for materials can be carried simultaneously. The mechanical
testing for the implants will ensue. The author expects to finish all preparations in the
summer and run the testing during the school year. A Gantt chart has been attached.
Task
Jun Jul Aug Sep Oct Nov
Literature Search
Manufacture Human Sternal Model and Test
Preparation of Material Mechanical Testing Site
S HeLa Cell Culture
Approval Usage of Animal Model and Ethical
Conduct
Obtaining Testing Materials from Manufacturer
Biocompatibility Test
Material Mechanical Test
Implant Mechanical Test
Table 1. Time Table of the Planned Experiment
Qualification of Researcher
Mr. Xin Li has extensive experience in the field of histology and microbiology. Mr.
Li is familiar with cellular fixation and staining. During his time in Dr. Xin Yu’s lab in
the Department of Biomedical Engineering, Mr. Li has completed hundreds of photoquality slides. On the other hand, Mr. Li is familiar with microbiological wet lab. For two
consecutive summers, Mr. Li has worked in Dr. Zijian Xie’s lab in the University of
Toledo, and mainly in charge of cell culture, cytotoxicity test, and cell count.
Although Mr. Li cannot claim to be an expert in the field of mechanical testing, he has
done a similar procedure for his senior design project --- he tested the tensile strength and
rigidity of ABS plastic for his helicopter model. Mr. Li is familiar with the basic process,
and understands the relevant physical laws. Mr. Li is a fast learner. It took him less than
two weeks to be proficiently familiar with the sectioning protocol using a microtome,
which is considered to be a difficult procedure.
In the end, Mr. Li has planned and organized experiments for almost three years. He
has been an active member of the Case Western community and demonstrated qualities
of a team player. Mr. Li has successfully collaborated with colleagues from multiple labs
in both Case School of Engineering and University Hospital.
Anticipated Audience Involvement
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The author would like to request for help in the area of both biocompatibility and
mechanical testing. The author would request to use the equipment in mechanical testing
lab from the Department of the Mechanical Engineering. The author would also like to
ask for permission to use the biocompatibility testing facility in Dr. James M. Anderson’s
lab from the School of Medicine.
The author believes that this study will advance our understanding in the field of
sternal reconstruction. The outcome of the study would possibly be used to formalize the
surgical method and material choice. In essence, this study will not only strengthen the
existing working relationship between the School of Engineering and the School of
Medicine, but also pushes our boundary of knowledge further.
Works Cited
1. S. Y. Lee, S. J. Lee, and C. S. Lee. (2011, Jan.). “Sternum resection and reconstruction
for metastatic renal cell cancer.” International Journal of Surgery Case Reports.
[Online]. 2.(4), pp. 45-46.
2. J. M. Galbis Caravajal, L. Y. Sanchez, C. A. Fuster Diana, R. G. Jorge, P. F. Ortiz, and
P. J. Deaville. (2009, Feb.) “Sternal Resection and Reconstruction after Malignant
Tumours.” Clinical and Translational Oncology. [Online]. 11.(2), pp. 91-95.
3. D. J. Cohen, and L. V. Griffin. (2002, Feb.). “A biomechanical comparison of three
sternotomy closure techniques.” The Annals of Thoracic Surgery. [Online]. 73. (2), pp.
563-568.
4. I. Sunil, S. Bond, and H. Nagaraj. (2006, Nov.). “Primitive Neuroectodermal Tumor of
the Sternum in a Child: Resection and Reconstruction.” Journal of Pediatric Surgery.
[Online]. 41.(11), pp. 5-8.
5. A. Watanabe, T. Watanabe, T. Obama, H. Ohshawa, T. Mawatari, Y. Ichimaya, N.
Takahashi, and T. Abe. “New material for reconstruction of the anterior chest wall,
including the sternum.” The Journal of Thoracic and Cardiovascular Surgery. [Online].
126.(4), pp. 1212-1214.
6. S. Milisavljevic, N. Grujovic, S. Mrvic, D. Stojkovic, M. Arsenijevic, and B. Jeremic.
(2012, July). “Sternum Resection and Chest Wall Reconstruction with Metaacrilate
Implant in Tuberculosis.” Indian Journal of Surgery. [Online]. 75.(1), pp. 257-260.
7. L. Prantl, S. Gehmert, M. Nerlich, C. Schmid, and E. M. Jung. (2011, Nov.).
“Successful Reconstruction of Sternum with a Scapular Autograft Segment: 5-Year
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8. T. Pedersen, H. Pilegaard. (2009, Apr.). “Reconstruction of the Thorax with Ley
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87.(4), pp. 31-33.
9. H. Liu, Y. Qin, S. Li, L. Li, Y. Cui, and Z. Zhang. (2011, Dec.). “Surgical Resection of
Sternal Tumors and Reconstruction with Titanium Mesh.” Chinese Medical Sciences
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10. J. R. Kerrigan, D. Bose, Z. Li, C. Arregui-Dalmases, E. Del Pozo, J. Ash, and J.
Crandall. (2010). “Response of the Sternum under Dynamic 3-point Bending.”
Biomedical Sciences Instrumentation. [Online]. 46. pp. 440-5.
11. M. Baleani, C. Peroni, L. Cristofolini, F. Traina, M. Silbermann, S. Sawaed, and M.
Viceconti. (2006, Jul.). “Multiaxial Miniaturized Load Cell for Measuring Forces Acting
Through a Sternotomy.” Experimental Techniques. [Online]. 30. (4), pp. 23-28.
12. V. Singh, R. Mir, and S. Kaul. (2010, June). “Aneurysmal Bone Cyst of Sternum.”
The Annals of Thoracic Surgery. [Online]. 89.(6), pp. 43-45.
13. K. Koto, T. Sakabe, N. Horie, K. Ryu, H. Murata, S. Nakamura, T. Ishida, E.
Konishi, and K. Toshikazu. (2012, Oct.). “Chondrosarcoma from the sternum:
Reconstruction with titanium mesh and a transverse rectus abdominis myocutaneous flap
after subtotal sternal excision.” Medical Science Monitor: International Medical Journal
of Experimental and Clinical Research. [Online]. 18.(10), pp. 77-81.
14. B. Voss, R. Bauernschmitt, G. Brockmann, and R. Lange. (2007, April).
“Osteosynthetic thoracic stabilization after complete resection of the sternum.” European
Journal of Cardio-Thoracic Surgery. [Online]. 32.(3). pp. 391-393.
15. A. Dell’Amore, A. Nizar, G. Dolci, N. Cassanelli, G. Caroli, G. Luciano, D. Greco,
A. Bini, and F. Stella. “Sternal Resection and Reconstruction for Local Recurrence of
Breast Cancer using the Sternal Allograft Transplantation Technique.” Heart, Lung and
Circulation. [Online]. 22.(3), pp. 234-238.
16. D. J. Cohen, and L. V. Griffin. (2002, Feb.). “A biomechanical comparison of three
sternotomy closure techniques.” The Annals of Thoracic Surgery. [Online]. 73. (2), pp.
563-568.
17. F. Kucukdurmaz, I. Agir, and M. Bezer. (2013, Jul.). “Comparison of straight median
sternotomy and interlocking sternotomy with respect to biomechanical stability.” World
Journal of Orthopedics. [Online]. 4. (3), pp. 134-138.
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18. Nakamura, M. Kawahara, H, Imai, K, Tomoda, S, Kawata, Y, and Hikari, S. (1983,
May). “Long-term Biocompatibility Test of Composite Resins and Glass Ionomer
Cement (in vitro).” Dental Materials Journal. [Online]. 2. (1), pp. 100-112.
19. Simon, M. (2013). “Method for testing the rigidity of large mechanical parts.”
Procedia Technology. [Online]. 12, pp. 334-338.
20. J. E. Losanoff, B. W. Richman, and J. W. Jones. (2004, Jun.). “Lower sternal
reinforcement to improve median sternotomy closure.” The Annals of Thoracic Surgery.
[Online]. 77. (6), pp. 2261.
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