Late Breaking News
For Upper Limb Amputees, the Real Advances Lie in the Future
- Categorized in: June 2009 Issue
WASHINGTON, D.C.—There is no wound that more boldly speaks to a person’s service in the military than the loss of a limb. While they still draw stares from the general public, men and women conﬁned to wheelchairs due to the loss of a leg, or with shirt sleeves pinned up to accommodate the loss of an arm, are not an uncommon sight in the halls of Department of Veterans Affairs hospitals and veterans halls. And, in the past, limb-loss would mean an irreversible loss of mobility and freedom. However, recent years have seen lower-limb amputees walking with the aid of robotic legs, or running full-sprint in track and ﬁeld events, thanks to the aid of ﬂexible metal prosthetics.
For upper limb amputees though, the real advances lie in the future. Fortunately, that future might not be too far away. A robotic arm currently being developed by the Defense Advanced Research Projects Agency in partnership with DEKA Research and Development Corporation is now being ﬁeld-tested in VA facilities with the goal of restoring functionality to amputees who have lost their arm up to their shoulder.
The Need for a New Prosthetic
“Historically upper limb amputation is relatively rare. Only about 3% of amputees have lost an arm or part of an arm,” explained Linda Resnick, PhD, a research scientist at the Providence VA Medical Center, and one of the lead investigators of what is being referred to as the DEKA arm, at a VA research press conference on Capitol Hill last month. “Those statistics have changed since the beginning of the conﬂicts in Iraq and Afghanistan. Today’s soldiers wear body armor that protect their core, but leave their extremities vulnerable. Twenty-two percent of new military amputees have lost an arm or part of an arm.”
“VA’s prosthetics and sensory aid service is the largest and most comprehensive provider of prosthetic devices in the world. But for upper limb prosthetics, there hasn’t been much available to veterans to date,” Dr. Resnick noted. As many as 25% of upper-limb amputees choose not to use any device at all because they are dissatisﬁed with them.
“The DEKA arm promises great advances in function,” she said. Those advances include an active socket that promises to be more comfortable, a mechanism that allows the user to choose the grip on the arm, and freedom of movement that mimics its ﬂesh and blood counterpart.
“Our upper limb has the most movement of all the limbs because we need to use it in space for ﬁne activity and skill. So replicating an upper arm is so difﬁcult because we have such degree of movement in the extremity,” Dr. Resnick explained.
But the DEKA arm promises to do that, she said. “This project will help position VA prosthetic and sensory aid and amputee care at the very cutting edge of technology,” she added.
Redeﬁning the Cutting Edge
The move towards that cutting edge began nearly 3 years ago when DARPA began its Revolution Prosthetics program—a $100 million investment in creating new prosthetic technology. The goal was to restore function to those that have lost it, not just to create a “neat robotic arm,” explained Col. Geoffrey Ling, MD, PhD. “How do you return function? That’s the goal of this program. It’s a far-reaching goal. We believe it pushes the extreme of technology and neuroscience,” Col. Ling explained. “As we set out to do this, we create for ourselves two large deliverables: building the ﬁnest electronic arm that we can, and restoring full function.”
The ﬁrst goal has been achieved. The second is distant, but not so distant that it is not in sight. “After only 30 months, we have had this great success,” Col. Ling declared.
The boast of “ﬁnest electronic arm” is not an empty one. The device looks like something cooked up in a Hollywood special effects studio, not something that could function on a practical level. But, function it does, and at a level not seen before in prosthetics. It rotates at the shoulder, elbow, wrist, and ﬁnger-joints. It can lift as much as 40 lbs and it allows the wearer to perform tasks far outside the scope of conventional prosthetics.
“One of the things we’ve done is, from a control perspective, create a number of different grasps. We have a grip here that’s equivalent to the hand,” explained Stuart Coulter, PhD, general manager at DEKA. Along with a partner, he demonstrated the performance of the arm, showing how it allows the wearer to pick up the smallest objects, and comfortably shake hands with someone.
“It’s possible to grip quite hard, so to make sure we don’t have a lot of veterans out there crushing other people’s hands, we’ve provided feedback,” Dr. Coulter said. “So when you grip, the veteran will get feedback about how much pressure he’s applying. This feedback is what allows you to pick up a grape without crushing it, and also pick up something quite heavy and hold onto it as well. The ability to do these things in parallel is a big advantage.”
The arm also allows the wearer to lift heavier objects, and to control the pressure exerted by the robotic ﬁngers. Dr Coulter demonstrated how the arm could pick up an electric drill and change the speed of the drill by changing the pressure exerted on the trigger. “Veterans always get a big smile on their face when they see this. You can hold onto the drill and adjust the speed of the drill as you go. With the current arms, the elbow lift capacity is only three or four pounds and [could not even hold the drill].”
The arm is still being tested for optimization in VA facilities with the goal of working out as many kinks in the device as possible before wider trials on veterans begin. Some of those kinks include making the arm light enough for female veterans.
“The weight/functionality trade-off is a big thing for prosthetics,” Dr. Coulter explained. “But part of that is perceived weight rather than actual weight. If you can bear the weight better, it seems lighter. We’ve worked on the socket in particular so the [patient] can bear the weight better. That’s a high bar to jump over from a weight to functionality perspective.”
Currently the whole arm weighs only 8 lbs. “And we’re constantly trying to ﬁnd ways to bring that weight down,” Dr. Coulter said.
The demonstration at the press conference utilized a fully functional assistant who had the controls strapped to one of his arms. However, such a method is untenable for amputees. “We don’t want to do what we’re doing here and have somebody follow you around with a good arm to run it,” Dr. Coulter quipped. “We’ve had to ﬁnd other ways to achieve control. One of the things that we do quite a lot of is a footpad. If you see somebody using the arm, you see their foot move back and forth.”
Wearers will rock their feet back and forth, using the relatively precise control provided by the muscles in the foot to guide the robotic arm, hand, and ﬁngers. The researchers have also been experimenting with using the contraction of muscles to trigger the arm’s controls—a method that has been utilized in previous robotic arms.
“The control problem is a very difﬁcult problem to solve,” Dr. Coulter admitted. Currently, the arm is exceptionally convenient considering how complex it is. “We’ve been calling it the strap-and-go arm, because you can just strap it on and go,” Dr. Coulter said. So, any control method should be similarly easy and noninvasive.
“We’re looking at how you can get a high degree of functionality by using noninvasive approaches, but it’s still limited,” Dr. Ling said. An amputee will not be able to use the arm to type on a computer, or play the piano or guitar. That will require the kind of interface that exists between the human brain and the nerves that control non-robotic limbs. “That interface exists between your brain and your central core. If you just think about the movement, you move,” Dr. Coulter said. And that is one of the next goals of the program: to create a control system using an amputee’s own thoughts to move the prosthetic.
“It’s an ongoing effort [to look] at ways to get true brain control of these assisted devices, as well as ways to get a sense of touch, a sense of temperature, a sense of vibration back in to the nerves,” Dr. Ling explained. “At this level of maturity at this time, this is where the program is. But we hope that we’ll soon have nerve controls.”