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Imagine a Soldier amputee whose prosthetic device is more than an extension of his body, it’s a part of it. That’s what a team of Army and Navy experts are working toward.

Walter Reed National Military Medical Centre in Bethesda, Maryland, is not only a centre of excellence for medical care, but also a hub of research and technological development. The most recent development out of the Orthopaedic Oncology Service is the Osseointegration Program, which began clinical trials in February.

An example of the lower-extremity osseointegrated prosthesis. In European studies the device is reported to have strengthened the bone it is attached to and give the patient a better sense of their limb in space, improving balance. (Photo courtesy of the Naval Medical Research Center)

“Osseointegration is the process of attaching an external prosthesis directly to the skeleton,” Navy Dr. (Cmdr.) Jonathan A. Forsberg said. “The term is really defined as a metal which is rigidly attached to bone, without any intervening soft tissue.”

While clinical trials have been ongoing in Europe for several years, this new program — a collaboration between the Army and the Navy — will be one of the first to perform clinical trials in the United States. It hopes to establish a network of patients at Walter Reed who have undergone OI procedures, and in doing so, build a referral center for the Department of Defense, Forsberg explained. They would be able to keep patients close and monitor their progress, and prove that OI benefits patients who have suffered combat-related limb loss.

Forsberg, the head of the Regenerative Medicine Department and an orthopedic oncologist, is working with U.S. Army Dr. (Lt. Col.) Kyle Potter, chief orthopedic surgeon for amputee patient care, to manage and implement the program. The two physicians work together on a daily basis, so collaborating on the program was a natural extension of their professional lives.

Though the two joke that Potter is the brain and Forsberg is the mouth, they both perform research and operate on patients. “(But) if you break things down into primary roles, I’d say that he’s the research guy and I’m the clinician,” Potter explained.

The program began when Forsberg and Potter observed a higher rate of heterotopic ossification — the formation of sand-like particles of bone in muscle tissue — in patients with combat-related injuries, Forsberg explained.

“(Potter) saw this phenomenon in amputees at Walter Reed and published a paper, and I published a series from this institution from all the patients with combat-related injuries, and we found an identical prevalence in about 63 to 64 percent of patients. That’s three times higher than the civilian sector,” he said.

Socket-based prostheses depend on the soft tissues around the bone to function, Forsberg continued. Many service members don’t have enough soft tissue, or durable soft tissue, to comfortably support a prosthesis, or they have developed complications like HO, making the prosthetic painful to wear. “Osseointegration relieves the pressure on the soft tissues, transferring it directly to the bone,” he said.

Potter said there are two main benefits to an osseointegrated prosthesis, the first of which is comfort. The prosthetic doesn’t hurt, sweat or feel heavy because it is pulling on a patient’s skin or soft tissue, and won’t cause rashes or skin breakdown, which are all problems associated with socket use, he explained.

“In addition to the added comfort … patients report that they have better control over their residual limb, and it’s more a part of them because the experience something called osseoproprioception, which is part of that altered perception. They can better feel where their limb is in space,” Potter said. Patients with lower-extremity prostheses also have better balance because they receive better feedback from the artificial limb.

A third advantage is that the bone the prosthesis is attached to will become stronger, Forsberg said. “We then restore the energy that is transmitted to the bone and improve bone health, which means increased bone-mineral density,” he explained.

Potter and Forsberg have engineered the OI program to test two prostheses simultaneously. One will come from the manufacturer Zimmer-Biomet, and the other from a Swedish company, Integrum, which developed the first truly osseointegrated implant — a dental implant now used all over the world.

“It’s a two-year process to enrol and treat the patients in both studies, and then we have two years of follow-up for that particular study,” Forsberg explained. “Since we have two options available to patients, one made by Integrum and one made by Zimmer-Biomet, we will really have four clinical trials, two in the upper, two in the lower, with two different implants, so that’s going to take us into the next five years, at least,” he added.

The two-implant approach lends flexibility to the study, particularly in the long term, as it enables them to customise the device to the patient, Potter explained. It also builds redundancy into the system, in case one device proves to be a dud, though the hope is that both implant brands will perform well.

“(People may) think that this is either crazy and barbaric,” Potter said, or ask ‘Why has this taken so long?’” Ten to 15 years ago, while he was still in training, he read about OI in Europe and found it interesting, but felt it wasn’t a good time to get on board with the technology.

An example of the upper-extremity osseointegrated prosthesis. In addition to the clinical trials of the OI devices that began in February, doctors at Walter Reed National Military Medical Center will be opening complimentary technology trials to test how to integrate things like myoelectric implants and provide patients with precise control of their limbs. (Photo courtesy of the Naval Medical Research Center)

“But over time, I think compelling evidence has developed, based upon European experience, and importantly, with more than just one implant,” Potter continued. “If it were just one implant in just one surgeon’s hands, then it’s probably not a sustainable technology, or somebody is fraudulently publishing results. So the track record has accumulated to the point that we think the safety profile is now acceptable in terms of the risk-benefit ratio for the appropriately selected patients.”

A December 2015 steering meeting helped establish the way ahead for OI clinical trials and prioritised studies of complimentary technologies, like myoelectric implants, which provide control signals for artificial limbs. One of the patients at the meeting, a man named Magnus, was wearing an upper extremity osseointegrated prosthetic with myoelectric implants that controlled it.

“What’s interesting about Magnus … is that not only did he come from about as far north in Sweden as you can get for the day to show us this, he also spends 100 percent of his time in that prosthesis. He never takes it off,” Forsberg said. Magnus feels as though the prosthetic is a part of him. Most patients only wear upper extremity prostheses for part of the day because they become so frustrating, Forsberg added.

Myoelectric implants and other technologies will help make osseointegrated devices state-of-the-art and increase patient function. With that in mind, Forsberg and Potter hope to open complimentary technology arms of the clinical trials within the next 12 to 18 months.

The Army is providing research, leadership and guidance for the way ahead as the program is built, Potter said. Support from the force is important because it not only enables the OI trials, but also helps build research infrastructure that makes any future expansion of the program cheaper and easier to facilitate, he explained.

There are several other organisations pursuing the development of osseointegrated prostheses, but Potter emphasises that they are not in competition. He wants everyone involved in the technology to do well in order to advance the state of the science and improve lives.

Forsberg said that in the future, they hope to be able to coat the entire prosthesis in living tissue, much like Luke’s robotic hand from the “Star Wars” franchise. There is also a sensor in development that can both detect infection in the tissue around the device and treat the infection using electrical current.

Potter emphasised that the OI program is not for everyone. Many amputees, for example, thrive with socket-based prostheses in daily life or when competing in professional sports — osseointegration devices are not for those people. Rather, they are for those who struggle with socket-based prostheses or have poor function.

“For those patients, I think the risk-benefit ratio makes the most sense. I think as osseointegration comes to the United States, we would have become leaders in amputation surgery and rehabilitative care over the global war on terror,” Potter said. “I think it’s not only advisable, but also incumbent on the Army and the Department of Defence to lead the way on this so we can advance the state of the science … and really improve this for the next conflict, whenever and wherever that should be.”

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