Saving Cyrano - how EOS additive manufacturing helped create a one-of-a-kind knee joint for a cat

1. Customer Case Study Medical
Facts
Cyrano the cat (above) is the first feline in the U.S to receive a Total Knee Arthroplasty (TKA). Femoral and tibial
components were created with a Direct Metal Laser Sintering (DMLS) system from EOS (Source: NC State University).
Saving Cyrano: How Additive Manufacturing
Helped Create a One-of-a-kind Knee Joint for a Cat
Challenge
Developing customised leg
prosthesis for a cat after
successful cancer treatment.
Solution
Manufacturing of prosthesis
with surface structures that
promote bone ingrowth.
Results
• Versatile: surface structure
depends on the intended use
• Customised: design of the
prosthesis considers bone
condition
• Biocompatible and resilient:
Cobalt chromium material
• Filigree: small prosthesis with
complex design

2. Cyrano escaped a leg amputation thanks to
laser sintered prosthesis
Short profile
The North Carolina State
University was founded in
1889 and is the state’s largest.
Its College of Veterinary
Medicine (CVM) is a dynamic
community whose members
are dedicated to preparing
veterinarians and veterinarian
scientists while advancing
animal and human health from
the cellular level through entire
ecosystems.
Address
NC State University
Raleigh, NC 27695 (USA)
www.ncsu.edu
For quite some time, Mr. Cyrano L. Catte II, an orange-and-white cat, had the perfect life. He had
a nice home in Upperville, Va., U.S.A., more than adequate food, and owners who loved him very
much. Then, at the age of nine, he got bone cancer in his left hind leg. Cyrano’s owners spared no
expense or effort. They took him to the University of Colorado, where he made instant veterinary
history by being the first cat to receive stereotactic radiation (focused beams aimed at the tumor)
therapy. Two sets of radiation cured his cancer – full remission – but one of the side effects was
bone deterioration of his distal femur and some on the upper end of the tibia as well. The normal
procedure for such a condition would be to amputate the leg. In Cyrano’s case, that was not recom-
mended: he weighed 26 pounds, and movement on three legs would be difficult.
Challenge
One potential alternative would
be a complete replacement
of the cat’s knee (stifle) with an
artificial one – a first in the U.S.
for felines. Cyrano’s intrepid
owners took him to the veterinary
facility at North Carolina State
University in Raleigh to met
with Dr. Denis Marcellin-Little,
a veterinary surgeon and
a professor of orthopedic, and
Professor Ola Harrysson of
the Industrial and Systems Engi-
neering (ISE) department.
Right away they recognized the
challenges: The implants have
to be very small and because of
the poor quality of the joint’s
bone structure stems were
needed to anchor the implant
components with the bones.
Just as quick, they decided using
Direct Metal Laser Sintering
(DMLS) from EOS to make the
two main components of the arti-
ficial knee. The addition of the
stems and the incorporation of
features to match up with custom
drilling and cutting guides gave
the metal components shapes that
were not readily manufacturable
by traditional molding or subtrac-
tive cutting processes.
There was also the issue of the
varied surface textures of the
final device. “From an orthopedic
standpoint, we wanted to include
different types of surfaces,”
Marcellin-Little says. The two
stems that extended inside the
hollowed-out femur and tibia
were slightly textured to promote
bone ingrowth. Further up on
the femoral and tibial components
was an area of porous mesh to
facilitate strong osseointegration.
While the stems provided short-
term stability for the implant, the
textured and meshed surfaces
would promote long-term stability.
Finally, the bearing surface at the
end of each cobalt chrome piece
had to be extremely polished
to enable smooth motion against
the polyethylene tibial mobile
The assembled
implant shows the
stems that insert into
the leg bones and the
bolts that fix them in
place. The complex
shapes of these
components would be
difficult to make with
traditional processes
(Source: NC State
University).

3. bearing surface, which would
rotate during leg movement.
Solution
Design started with 3D data from
CT scans of Cyrano’s good and
bad hind legs. 3D design models
of the implant components were
made using MIMICS software
from Materialise. “We started from
one of BioMedtrix’s knee implants
for dogs and miniaturized it,”
Marcellin-Little says. “We added
the stems, the bolts that hold the
stems in place, and other features
unique to this design.” The result
was very sophisticated compared
to other feline implants currently
in use. “We incorporated features
from human devices,” Harrysson
says. “The trick was in making
them small enough for a cat –
think of a finger joint prosthesis,
which would be about the right
size.”
The metal component models were
manufactured at EOS’ global
headquarter in Krailling, Germany,
sent to BioMedtrix for finishing
and then the DMLS parts were
ready for handing off to the sur-
gical team.
Results
DMLS can work with a number of
different metals. Titanium is great
for bone ingrowth but it is much
softer than cobalt chromium.
“The loads on a titanium femoral
head would wear the metal down
eventually. Because the implant
components would already be
thin in some places, they might
be subject to breaking or cracking
if they eroded still further. Cobalt
chromium was our best choice,”
Marcellin-Little points out.
All these textures were possible,
and fairly easy to create, by using
Additive Manufacturing. “The
EOS technology not only gives us
design freedom for orthopedic
implants,” Harrysson says. “It also
offers the means to build osseo-
integrated surfaces directly into
the part.” Traditionally manu­
factured implants often have
surfaces added in post-processing,
such as multiple layers of beads
sintered on manually. Plasma
spraying and other surfacing
techniques are not as accurate as
DMLS, which allows designers to
specify the pore size, density, and
the layout of the porous section.
Key to the project was assembling
a multi-talented design and manu-
facturing team, which consisted
of 16 experts and spanned five
states and two continents. “This
kind of implant had never been
made before, and this surgery
never attempted,” Marcellin-Little
says.
The surgery, which took six hours,
went smoothly. “As we suspected,
Cyrano’s distal femur had very
poor bone quality,” Marcellin-
Little notes. “Without the stems
that we had designed in, the
femoral component would not
have been stable at all, even if we
had used polymethylmethacrylate
bone cement.”
Afterwards Cyrano began the
long road of rehabilitation and
therapy that would lead to his
recovery. He did well. Besides
his observable limp, he is able to
use the leg and joint. “Cyrano
was a perfect patient, very cool
and very calm,” Marcellin-Little
says. “He is much more comfor-
table than he had been since
the cancer developed, and he’s
pleased, and his owners are
pleased.”
“The main change this techno-
logy has brought is that the
manufacturing process is no
longer a barrier to the imagina-
tion of an orthopedic clinician
who needs to create something
very specific.”
Dr. Denis Marcellin-Little,
Veterinary Surgeon and
Professor of Orthopedic
Surgery in the College of
Veterinary Medicine at
NC State
“What we learned from the
Cyrano project is transferable
to other animals and even to
human medicine. Now that we
know how to miniaturize a
joint this sophisticated there
are a number of potential
applications, in hands or jaws,
for example.”
Ola Harrysson, Professor of
the Industrial and Systems
Engineering (ISE) department
at NC State

4. Status 4/2013. Technical data subject to change without notice. EOS is certified according to ISO 9001.
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