Intern, Spring 2015
As with many
important innovations, the use of prosthetics did not begin as recently as people
might assume. In fact, the world’s
oldest prosthesis dates all the way back to at least 710 BCE, when the Egyptian
daughter of a priest lost her right toe, possibly due to gangrene, and was in need
of a replacement. It was well crafted from wood and leather, and had holes for lacings
to attach directly to the foot or fasten to a sandal. Needless to say, prosthetic
technology has come a long way since then.
When most people think of prosthetics, they likely think of
a hunk of plastic that’s basically lifeless, much like the Egyptian toe—and
they wouldn’t be wrong, especially as that’s what many prosthetics are, particularly
for upper-limb amputees. As a result, up to half of these amputees choose not to
wear a prosthetic device because the replacement limb is too uncomfortable and doesn’t
bring back what many amputees really desire: sensation.
However, at Case
Western Reserve University, Dustin Tyler is seeking to change that. As the
research director and associate professor of biomedical engineering, he and his
team developed a hand system that allowed their two amputee testers to feel
normal hand sensations. The prosthetics are so sensitive, in fact, that the
amputees could even identify textures and pick up objects as small as grapes
and cherries with the correct amount of force, so as not to squish them. The
hand system also caused phantom limb pain to essentially disappear, an
unexpected but not at all unwelcome side effect.
How is this possible? Tyler and his team used ideas similar
to those behind the treatment known as targeted muscle
reinnervation (TMR), developed by scientists at the Rehabilitation
Institute of Chicago (RIC). This treatment involves a surgery that takes the nerves
that once controlled the amputated limb and reroutes them to another place, such
as the chest, so that when an amputee thinks about moving their arm, the signals
move the chest muscles instead. Electrodes attached to the chest register this movement
and move the prosthetic.
Pretty cool, right? While TMR focuses on the nerves used
for movement, Tyler’s team worked with the nerves used for sensation—by
connecting them to a machine through electrodes to establish the signals
necessary for the brain to process sensory feedback. Unfortunately, at the moment,
Tyler’s system requires the electrodes to penetrate the skin, which can easily cause
an infection. However, Tyler hopes to develop a fully implanted system that
will allow the wearer to connect to the prosthetic arm via Bluetooth, which takes
the prosthesis to a whole new level by using a wireless interface.
Several states away, Leslie Baugh
made history at Johns Hopkins University’s Applied Physics Laboratory (APL) by becoming
“the first bilateral shoulder-level amputee to wear and simultaneously control”
the lab’s Modular Prosthetic Limbs (MPLs). Baugh also underwent TMR surgery. After
only ten days of training, Baugh could move small objects like cups, demonstrating
the intuitive nature of the control.
Both types of prosthetic devices are still in the testing phase
but might be on the market in as little as ten years. Perhaps they could even
be combined into a single device that enables both movement and sensation. Either
way, it’s starting to look like a brighter future is finally here for amputees.
Did
You Know?
If amputees aren’t completely satisfied with the current options
for prosthetics, they do have another option: transplant
surgery. Although it is an experimental procedure for many hospitals, there’s
been success with hand, arm and even leg transplantation. As with organ transplants,
the patient receives the limb from a deceased donor and must commit to extensive
rehabilitation and a lifetime of taking immunosuppressive medications that prevent
rejection. However, it can be worth it. Brendan
Marrocco, an injured soldier who received a double-arm transplant in 2013, reported
movement in his arms only a month after the surgery.
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