ADDITIVE MANUFACTURING feature
FAR LEFT:
Design as given to the Surgeon
prior to build
LEFT:
Mesh seen in Computed
Tomography image (CT scan)
RIGHT:
Mesh as seen in Magnetic
Resonance Imagery (MRI scan)
BELOW:
The Arcam EBM S12 system
porous polyethylene. Once the opening becomes large enough,
“
should contaminate it, we can find ourselves in the operating
or incorporates an area of compound curvature, a custom room with the patient ready for the implant, but unable to
implant becomes a necessity for protection and long-term continue with the surgery. This puts the surgeon in an
maintenance of contour.
The requirement
impossible position and endangers the patient unnecessarily.
For many years, the standard implant for these areas was the
for sterility is
In addition to sterilisation, we faced the issue of removal of the
custom PMMA (polymethylmethacrylate) implant. These are
absolute, but
infected implant in patients with recurrent infection, followed by
currently produced using a stereolithography produced master, months of healing, then creation and implantation of a new
which is embedded in a two-part flask, then removed and without the ability prosthesis. The cost of these new surgical procedures and
replaced with PMMA resin, which is laboratory processed with hospitalisation is extremely high, and does not take into
pressure and heat. In large implant cases, the flask can weigh
to re-sterilise a
account the additional risk and discomfort placed on the patient
over 50 pounds and is limited in contour complexity.
custom implant if
involved.
Polishing, drilling for dural fixation and gas sterilisation using
something should
A solution was required to these problems. As part of our
Ethylene Oxide (EtO) are also carried out prior to delivery. decision matrix, we pooled all of our knowledge resources for
These implants are successfully used on many patients around contaminate it, both the manufacturing of implants and surgical implantation of
the world. However, the EtO sterilisation equipment is not the finished device. The surgeons requested the following:
available in many locations and is being phased out or banned
we can find
standard available, non-gas sterilisation methods; porosity to
in many hospitals because of its environmental effect.
ourselves in the
reduce trapped fluid pooling under the implant; compatibility
with tissue ingrowth to reduce the free space for infection;
Another alternative to PMMA is PEEK (polyetheretherketone).
operating room
ability to conform to complex contours and thickness changes,
PEEK
1i
can be purchased as a medical grade plastic, which is regardless of location; and lastly, the implant must be visible on
normally injection moulded, but in our case must be milled to
with the patient
radiographs without causing radiographic artifacts and be safe
the correct shape because of the high cost of the custom to use with MRI (Magnetic Resonance Imaging).
tooling. Due to its high temperature characteristics, it does not
ready for the
require gas or EtO sterilisation, and can be autoclaved in any
hospital operating room steriliser. This has distinct advantages,
implant, but
The only material available to us for this purpose was titanium
alloy, with its proven biocompatibility, strength and, most
but because of the extremely high cost of the initial block, it is
unable to
importantly, its ability to promote fibrovascular ingrowth. The
cost prohibitive. only manufacturing method capable of producing such a
continue with the
complex geometric structure is additive-based.
In both of the previous cases, there is an additional factor that
must be taken into account, which is that human tissue does
surgery
The primary implant we have produced since we began using
not bond to plastic. This results in loss of muscle attachment to direct metal manufacturing is the 3D mesh, titanium cranial
the skull replaced by the implant, and the formation of scar plate. The reason for our choice of mesh versus solid is well
tissue that encapsulates the implant provides an area for
bacterial growth that cannot be reached by antibiotics. In
patients with a history of antibiotic resistant infections, this can
result in the loss of the implant if a recurrence of the infection
appears. These factors do not affect most recipients of PMMA,
PEEK, or porous polyethylene implants, such as MedPor
2
, which
does encourage fibroblast ingrowth.
”
defined above and medically specific for a particular group of
patients, but the simple fact is that the 3D mesh could not be
produced using any other technology. The surgical cases we are
dealing with, particularly in the cranial injury patients, require
very large, complex curvature implants to close the surgical
opening in the bone of the skull. The large craniectomy, or
surgical cranial bone removal — done immediately after the
injury to allow decompression of the damaged brain tissue —
The aforementioned issues of sterilisation are becoming more results in extremely good survival rates for injured patients, but
important as the environmental issues become more of a factor requires a massive implant to close the area and provide
in our processes. The requirement for sterility is absolute, but aesthetic contours once the patient is ready for the permanent
without the ability to re-sterilise a custom implant if something repair of the skull. Many different materials have been used for
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