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Dynybil |
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Home
Institution
Medizinische Hochschule Hannover
Host
Institution
Laboratory
for Soft Tissue Research, Weill Medical College of Cornell University
and Hospital for Special Surgery (HSS), New York
Mentor: Scott A. Rodeo, M.D.
E-Mail
cdynybil@hotmail.com
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Research
Topic
see Abstract |
Personal
Reactions to the U.S. Experience
Differentiating between the locations of the United States, I think that
a stay for a period of several months in a (The!) city like New York teaches
you to manage your day very well. I had already been in NY three times before,
but this was the first time that I got the feeling of really being involved
during the week-day, doing my "job", and staying "cool" with regard to the
mass of attractions and events in this city, knowing that there would be
enough time, especially on weekends, to do what I wanted to do.
I cannot agree with what people say at home in good old Germany, that people
in the U.S. are "superficial." When I came back to the Hospital for Special
Surgery after two years, I got such a warm welcome. On the first weekend
there was a dinner that the staff organized for me, a party after that,
and the rest of that weekend to recover.
Staying in the USA after September 11, one cannot ignore the atmosphere.
Even four months after that dreadful attack you see American flags on cars,
buildings, and stores everywhere and the slogan "United We Stand" becomes
manifest. Sometimes it is a little overdone, but it is meant honestly and
it is easy to understand, especially when you are in New York. |
Greatest
Difficulties Encountered
: The same old story: start to deal with the bureaucracy as soon as possible.
The American embassy may not be the problem, but rather the officials of
your host institution. It is not that they might have something against
you but it is sometimes very hard to make them understand that you did not
expect that the drawing up of the IAP-66 would take over three months. The
visa itself I got within four days from the American embassy. |
Most
humorous incident
One of many humorous incidents happened when some guys and I came home at
4 AM after intensively researching local spirits. The accommodation we lived
in was the Catholic Kolping House, a very serious institution. When we tried
to get in, the keyhole seemed to have a life of its own at this time of
night. A car stopped and the driver asked me about the requirements for
living in the Catholic Kolping House, because he was searching for accommodation
in NY. When he asked me for my name, I told him "I am Christian"; "No",
he said, "I am not interested in your religion." Being not quite clear-headed,
I said, "but this is true." It took a quite long time to clear up that misunderstanding.
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Helpful
Hints for Future Students
1) Ms Birgit Heller and Mrs Laurie Williams
2) Catholic Kolping House, 165 East 88th Street (for stay in NY)
3) Start early to save money for your stay, especially for a stay in NY!
4) There are three main points you should remember in order to spend a nice
time in the US: be friendly, motivated, and open-minded to the sometimes
crazy manner of the people in the States. |
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Abstract
on Research Topic:
Studies of the Cellular and Molecular Mechanism of Tendon-to-Bone Healing
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Introduction
and hypothesis:
Despite generally favourable results with ACL (Anterior Cruciate Ligament)
reconstraction, instrumented testing of knee stability demonstrates frequent
mild residual anterior laxity, which may lead to recurrent instability.
Failure of secure healing of the tendon in the bone tunnel prior to return
to activity can result in graft slippage in the tunnel with resultant
laxity. Impaired healing may occur in circumstances in which there is
excessive motion at the graft-tunnel interface, such as may occur with
non-isometric graft placement . Recently, expansion of the bone tunnel
following ACL reconstruction has emerged as a clinical concern, with radiographic
evidence of bone resorption. The etiology of tunnel widening is not currently
known but may be caused by graft-tunnel motion, synovial fluid influx
into the tunnel, or inflammatory cytokines. Although tunnel widening has
not been related to recurrent knee laxity to date, there is concern about
its effect on long-term graft fixation. Furthermore, bone resorption around
the bone tunnel is likely to complicate graft revision surgery. A better
understanding of the basic mechanism of tendon-to-bone healing and tunnel
widening may allow development of methods to improve healing in these
situations. To allow a better insight to this mechanism Dr. Rodeo (Orthopaedic
Surgeon and Principal Investigator in this area at the Hospital for Special
Surgery) developed an animal model of tendon healing in a bone tunnel
to study the healing process at macrostructural level. Following studies
intend to provide new insights into the cellular and molecular mechanism
at the microstructural level. For these we set three major hypothesis:
1) osteoclastic bone resorption causes expansion of the bone tunnel, and
thus limits tendon-bone interdigitation (healing);
2) healing (interdigitation) can be enhanced by increased osteoblastic
bone deposition at the tendon junction;
3) enhancement of healing will result in improved attachment strength
between tendon and bone
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Specific
aims and experimental strategy:
As a basic background we are using an established rabbit model of anterior
cruciate ligament reconstruction in which a tendon graft is transplanted
into bone tunnels in femur and tibia. As controls we are using the same
rabbit model without tendon graft transplantation to differ the effect on
the development of tendon-bone interface tissue induced by the transplanted
tendon graft. The histologic and molecular analysis is distributed due to
the sacrification of the rabbits after one, two, three, four, eight and
sixteen weeks. Histologic analysis is done by Haematoxilin and Eosin staining,
looking for the development of cellular tissue in the interface and ectopic
bone and interdigitation of bone to tendon respectively and by von Kossa
staining to detect mineralised tissue. For histochemical localization of
tartrate-resistant acid phosphatase (TRAP) to identify osteoclasts the sections
will be stained after the procedure described by Minkin. Quantitative histomorphometry
is carried out using computerized image analysis using Sigmascan Pro software.
The femoral and tibial bone tunnels will be isolated and high resolution
radiographs will be made of the bone tunnel. The bone tunnels containing
the tendon graft will then be fixed in 2% paraformaldehyde plus 0.5% glutaraldehyde
in 0.05M cacodylate buffer, pH 7.4 at 4°C. Fixation time will be limited
to no more than 18 hours in order to preserve phosphatase activity and tissue
morphology. The sections will then be embedded in JB-4 resin. The tissues
will be dehydrated to 100% ethyl alcohol in step-wise dilutions and then
transferred to JB-4 Solution A. The tissues will be put through two changes
of this resin at 4° C for 12-24 hours and then new JB-4 resin with accelerator
will be used for embedding. The samples will be placed into the freezer
(-20°C) to polymerise. Sections will then be cut using JB-4 microtom and
glass knives. Five-micron thick sections of these tissues will be cut and
stained with haematoxilin and eosin for routine histologic ealuation using
light microscopy. The sections for TRAP examination will be incubated on
slides in following solution: 5 mg of Naphtol AS-BI phosphatase, 4 rops
of DMSO, 25 ml sodium acetate buffer, 0.1M, pH 5.0, and 25 ml water. Immediately
prior to use 20 mg of Fast Garnet is added, followed by 485 mg of tartaric
acid. The slides will be incubated at room temperature for 2 hours. After
incubation, the sections will be counterstained with methyl green. The positive
TRAP reaction is rust or dark red in color. With regard to the first hypothesis
we intend to apply Osteoprotegerin to the tendon and bone at the tendon-bone
interface. Osteoprotegerin servs as an osteoclast inhibitor, which proposes
improved healing by closer apposition of new bone to the tendon graft. Osteoprotegerin
ligand (OPGL), which stimulates osteoclast development , will be used as
positive control. The mechanism of this hypothesis will be examined by using
histomorphometric and histochemical analysis and additional quantitative
mRNA analysis. The second hypothesis will be tested by using bone morphogenetic
protein-2 (BMP-2), which stimulates ossification, to restrict tunnel expansion
and increase ingrowth of bone into he tendon. The third hypothesis we will
examine by using macrostructural criteria of ultimate load-to-failure testing
to evaluate the agent (Osteoprotegerin or BMP) that resulted in the best
healing by microstructural criteria in first and second hypothesis. This
will be accomplished using biomechemical testing to measure the strength
of the healed tendon-bone attachment. |
Final
aim:
The pharmaclogic agent (OPG or BMP-2) that results in the best enhancement
of healing will be used in future studies to evualuate a factor separately
in order to understand its effects, and to gain further insight into the
molecular and mechanical signals which regulate tissue regeneration, the
intracellular pathways that result in healing of tendon-to-bone, and how
the tendon insertion site is formed in the skeleton bone. For the pharmacologic
agent that is effective in this application future studies will be designed
to establish efficacy in a larger animal model. |
