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Johnny Matheny, a former commercial baker from Redhouse, Virginia, lost his left arm to bone cancer in 2008. He now wears a hook-style prosthesis strapped onto his chest; he can laboriously open and close the hook and move the arm up and down by flexing certain muscles. But he is avidly awaiting new technology that he thinks will work much better: a surgically implanted device that attaches directly to bone, potentially enabling superior range of movement and more precise control.

The devices have been tested in people for more than a decade in Europe, but they carry significant risks. Because they require a connection that protrudes through the skin, infections are fairly common, often requiring secondary surgeries. Scientists in Europe and the U.S. are trying to develop ways to better integrate the device with the body—creating stronger connections between metal, bone, and flesh—in order to reduce this risk.

“We are very hopeful. The fact that folks who received the implants are ambulatory means that their quality of life is obviously much better than it was,” says Grant McGimpsey, director of the Bioengineering Institute at the Worcester Polytechnic Institute. “But we need to think about [infection risks] before implementing it in large numbers of people. We are looking for a prosthetic solution that will last 70 years.”

The prostheses currently available to amputees fit over the wearer’s stump. While they can vastly improve quality of life, allowing many people to walk, for example, they also have serious disadvantages. Walking can be quite painful, and friction between the stump and the socket of the prosthesis can lead to chronic sores and infection. “Overwhelmingly, the biggest reason people can’t walk after amputation is because they can’t wear a socket,” Richard McGough, an orthopedic surgeon at the University of Pittsburgh.

With so-called osseointegrated implants, which attach directly to bone, a cylindrical device is surgically inserted into the hollow of the remaining bone. The goal is to encourage the bone to grow into the metal, similar to what happens after joint replacement surgeries. The artificial limb itself attaches to a short connector that protrudes from the skin, eliminating some problems of socket prostheses.

To date, many of the implants of this type have been performed in Germany, under the guidance of Horst Aschoff, director of the department of Plastic, Hand, and Reconstructive surgery at the Sana Clinic, in Lubeck. His team has treated more than 50 patients over the last decade. Aschoff’s research shows that people with the lower-limb implants move more naturally than those with traditional prostheses, have a more symmetrical gait, and use less energy to perform the same movement.

But the procedure is still quite risky. “The biggest hurdle is fear of infection,” says McGough, who has collaborated with Aschoff. “There are not a lot of other systems in medicine where you deliberately have a hunk of metal sticking out of skin.” According to a survey of 40 of Aschoff’s patients who received implants between 2003 and 2009, about half had to undergo a second surgery to deal with infections or other complications. Five had their implants removed. However, 38 of the 40 said they would undergo the original surgery again.

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Credit: Gordon Blunn, University College London

Tagged: Biomedicine, biomedical devices, prostheses, prosthetic arm, artificial limb

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