Recovery 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.
"The time 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.
The original 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.
The rapid prototyping market gravitated to inexpensive 3D printers that can quickly make models from a wide range of materials, mostly plastic. High-End Focus
Higher-end 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.
One living, 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.
He received emergency treatment in Iraq and Germany, and doctors told his family he might not survive.
W. Lee 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."
Following 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.
After months of rehabilitation, Sgt. Statzer learned to walk again and recovered most of his memory.
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."SLA Master
The standard 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.
"In large 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.
One 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.
An 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.
PEEK 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.
According to 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.
The biggest problem, however, is that human tissue does not bond to plastic.
"This 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."
The plastic cranial implants at Walter Reed needed to be removed about 12 percent of the time to save the patient's lives.