rates for American soldiers with head wounds are improving significantly
because of new technology to quickly produce custom cranial implants that are
more resistant to infection.
More than 70
cranial plates have been produced using the new process at Walter
Reed Army Medical Center (WRAMC) in Washington, D.C., with an average
surgical time of 90 minutes from first incision to completion of suturing. Previously,
the same types of surgeries took from two hours to more than six hours.
savings can be directly attributed to the improved implant design and attached
fixation," says Stephen L. Rouse, DDS, a government contractor working in the 3-D Medical Applications Lab at Walter Reed Army Medical Center. "Large implants were previously multi-piece constructs,
and were slower to place and fixate."
At the heart
of the process is advanced application of 3-D digital scanning and high-powered
additive manufacturing equipment that can make highly accurate custom shapes in
medical-grade titanium alloys.
systems were based on lasers that created 3D shapes in processes called
stereolithography (SLA) and selective laser sintering (SLS). Both are owned
today by 3D Systems of Rock Hill, SC.
prototyping market gravitated to inexpensive 3D printers that can quickly make
models from a wide range of materials, mostly plastic.
additive manufacturing equipment is increasingly focusing on dental, medical
and aerospace applications, where engineers greatly value the ability to create
precise, complex, strong parts often not possible with injection molding
because of high costs or process limitations.
The work at
Walter Reed improves life expectancy and quality of life for wounded soldiers.
breathing example is Paul Statzer, who was a world champion weight lifter in
2000. He was a veteran of the first Gulf War and decided to re-enlist. His unit
was sent to Iraq, and in 2005 he was investigating craters created by roadside
bombs. An improvised explosive device detonated near Sgt. Statzer, removing
much of his skull, his eye and parts of his larynx.
emergency treatment in Iraq and Germany, and doctors told his family he might
Warren, the surgeon who did the initial brain surgery on Sgt. Statzer at the
332nd Air Force Theater Hospital in Balad, Iraq, says: "My memory of Paul
Statzer was of a man so desperately injured that even while operating on him I
gave him no chance for survival."
emergency surgery and a transfer to Germany, Sgt. Statzer was taken to Walter
Reed where Rouse's lab performed a 3D scan of the cranial opening and made a
plastic implant to replace the missing bone. Bone grafts and skin grafts
replaced the missing area around his left eye.
of rehabilitation, Sgt. Statzer learned to walk again and recovered most of his
Last year, Warren
had a tearful reunion with his former patient in Pittsburgh near Sgt. Statzer's
home. He recalls the surgery in a recent book: "Called Out: A Brain Surgeon
Goes to War."
cranial implant is made from PMMA (polymethylmethacrylate). A
stereolithography-produced master is embedded in a two-part flask. The master
is then removed and replaced by PMMA resin, which is then processed in a
laboratory with pressure and heat.
implant cases, the flask can weigh over 50 pounds, and is limited in contour
complexity," says Rouse. Polishing, drilling for fixation and gas sterilization
using ethylene oxide (EtO) is done prior to delivery to the operating room.
significant problem with that approach is that EtO sterilization equipment is
not available in many locations, and is being phased out or banned in many
hospitals because of environmental issues.
alternative material used for transplants is PEEK (polyetheretherketone). The
great advantage of PEEK is its high-temperature tolerance (its glass transition
is 143C). PEEK can be autoclaved in any hospital operating room sterilizer,
eliminating the requirement of gas or EtO sterilization.
implants must be milled to exact shapes because of the expense of tooling.
Rouse says that the cost of medical-grade PEEK blocks is very high.
industry sources, medical grade PEEK costs close to $400 per pound compared to
about $44 per pound for industrial-grade PEEK. A leading medical-grade PEEK
producer declined to comment on the cost issue.
problem, however, is that human tissue does not bond to plastic.
results in loss of muscle attachment to the skull replaced by the implant, and
the formation of scar tissue which encapsulates the implant provides an area
for bacterial growth that cannot be reached by antibiotics," says Rouse. "In
patients with history of antibiotic-resistant infections, this can result in
the loss of the implant if a recurrence of the infection appears."
cranial implants at Walter Reed needed to be removed about 12 percent of the
time to save the patient's lives.
the surgical teams at Walter Reed brainstormed the implant problem.
from surgeons included:
Standard available non-gas
Porosity in the implant to reduce trapped
fluid pooling underneath;
Material compatibility with tissue
ingrowth to reduce the free space for infection;
Ability to conform to complex
contours and thickness changes, regardless of location; and
The implant needed to be visible on
radiographs without causing radiographic artifacts and be safe to use MRI
(magnetic resonance imaging).
material available to us for this purpose is titanium alloy, with its proven
biocompatibility, strength and most importantly, its ability to promote
fibrovascular ingrowth," says Rouse. "The only manufacturing method capable of
producing such a complex geometric structure is additive-based."
officials selected a new technology developed in Sweden by a company called
Arcam using the electron beam melting technique (EBM).
In the EBM
process, fully dense metal parts are built up layer-by-layer as metal powder is
melted by a powerful electron beam. Each layer is melted to the exact geometry
defined by a 3D CAD model.
takes place in a vacuum at elevated temperatures, resulting in stress-relieved
parts with material properties better than cast and comparable to wrought
material, according to Magnus René, CEO of Arcam.
system is designed to provide a base pressure of 1x10-4 or better throughout
the entire build cycle. The EBM machine produces precise titanium mesh shapes
that allow bone ingrowth and prevent fluid pooling under the implant that can
lead to infection.
technology is also used to make off-the-shelf orthopedic implants. René says
that pores can be engineered to improve bone fixation. The goal is to improve
bone ingrowth compared to current technologies of coating cobalt-chrome
implants with titanium beads or other materials.
implant technology is working well at WRAMC.
rates in the past three years have dropped to 4 percent. "None have had to be
removed following the healing process," says Rouse.
such as Selective Laser Melting (SLM by MTT Technologies, Staffordshire, UK),
and Direct Metal Laser Sintering (DMLS by EOS, Munich, Germany), were not
available in the U.S. when Walter Reed began its testing.
are designed after segmenting CT scan data using Mimics software from
Materialise that allows engineers to bridge 2D data to 3D. 3Matic, also from
Materialise, and/or FreeForm Modeling Plus, from Sensable, are used for the
actual implant design.
be built in both mesh and solid, and the implant design includes the fixation
plates. A skull model is created using a stereolithography machine and is sent
with the completed implant to the surgeon for approval.
Seven Day Limit
Speed is a
"Our goal is
to keep the entire process, from CT scan to delivery of the finished implant,
to seven days," says Rouse. "In most cases, we are successful. Some of the
issues, or problems that we have experienced include intermittent build
failures, machine availability and shipping delivery delays."
Rouse has faced is lack of space for a program that is rapidly growing due to
its huge success.
additive manufacturing machines are scattered across the Walter Reed campus
where space permits. That changes soon under the Base Realignment Program
(BRAC), which is designed to make more efficient use of military assets.
group will soon move to a medical campus in Bethesda, MD, about six miles from
WRAMC, which is located near the outer border of Washington, D.C. The new
campus will be called the Walter Reed National Military Medical Center at
equipment and three-person staff will be in one location at the new medical center. That
equipment includes an SLA 7000, SLA 500, Z Corp. 650, Z Corp. 450, and an Arcam
A-1. On order is a Connex 500 from Objet Corp.
equipment serves a myriad of roles, ranging from pre- and post-surgical medical
models to custom cranial implants, subperiosteal dental implants, facial bone
implants and custom fixation devices.
Use of the
additive manufacturing machinery is not necessarily simple, unlike milling
machines, which can be left unattended.
monitoring to make sure there has been no warpage of the part. It's also
important to ensure that the part is being produced to specification
the Ti6Al4V powder must be monitored for oxygen content. The final part must be
tested to ensure that metallurgy is within specifications. Vigilant preventive
maintenance is required to make sure machines are available when needed. Units
like the EBM machine are too expensive to have backups on hand.
line for this entire process is the ability to build an implant that is
designed for a specific patient's needs, that reduces the operating room time
requirement significantly, and provides better outcomes with more resistance to
infection," says Rouse.