SEATTLE (Ivanhoe Newswire) - There are two million people with amputations in the U.S. For many of these patients, prosthetic devices offer greater mobility. Now, researchers are testing a new generation of prosthetics that are like nothing you've seen.
Not much slows down Zac Vawter. Not even an amputated leg.
"I lost my leg in a motorcycle accident," Zac told Ivanhoe.
Zac received this prosthetic. It helps him get around, but has its limitations.
"If I were to sit down and leave the knee locked, it would stay locked," Zac explained.
But this thought-controlled myoelectric leg does what Zac's prosthetic can't. Before Zac could use it, orthopedic surgeon Doug Smith took nerves from his lower leg and redirected them to his hamstring muscle.
"Instead of firing when you think about bending your knee, it would fire when you think about raising your ankle," Doug Smith, MD, Orthopedic Surgeon, Harborview/UW Medicine, told Ivanhoe.
When Zac wants to move the leg, the brain signal travels down his spinal cord, through the nerves; electrodes in the prosthetic pick up signals from the muscles.
"You can have a prosthetic device that actually works according to your thought," Dr. Smith said.
The device is still being studied, so Zac can't take it home, but he looks forward to the day he can.
"Stairs with that leg, the ‘bionic leg,' is really phenomenal," Zac said.
Until now—only thought-controlled arms were available. Although the cost of the "bionic leg" hasn't been determined, researchers say a version could be available for consumer use within three to five years.
BACKGROUND: Prosthesis is an apparatus that is used to restore the function of a limb with a prosthetic replacement. A prosthetic replacement can reinstate the use of the legs, arms, joints, eyes, and hands. When a person needs a prosthetic limb usually it is because of a tragic accident or disease. When a person has to have an amputation, they are losing the function of that body part. Thankfully, doctors have created prosthetic body parts to replace the function of their biological body part. (Source: http://www.nlm.nih.gov/medlineplus/ency/article/002286.htm)
BENEFITS: Those who have undergone the process of having a prosthetic limb have been known to have more energy. Those who decided to continue to use crutches and a wheelchair did not have the same amount of energy that prosthetic limb recipients had. Patients who have prosthetic limbs also have more mobility. Those who have prosthetic legs have the ability to go up and down the stairs and reach places that are not wheelchair accessible. Prosthetic limbs also offer a sense of independence that others do not have. (Source:http://www.livestrong.com/article/36509-advantages-prosthetic-legs/)
MODERN PROSTHETIC LIMBS: Prosthetic limbs have advanced throughout the years. They have grown to be lighter, more realistic, and stronger than older prosthetics. They are also easier to grip and walk in, and they provide more comfort. Although prosthetic limbs have evolved from earlier days, each prosthetic is tailored and specific to the person receiving it. (Source:http://science.howstuffworks.com/prosthetic-limb2.htm)
"BIONIC LEG": The latest technology for prosthetics is the "bionic leg." Scientists have designed a bionic prosthetic leg that can reproduce a full range of ambulatory movements by communicating with the brain of the person wearing it. The prospects for such connections between a patient's prosthetic and their peripheral nerves are generally dim. In most amputations, the nerves in the thigh are left to die. A neurosurgeon at UW Medicine, Dr. Todd Kuiken, pioneered a practice called "reinervation" of nerves severed by amputation. Dr. Doug Smith was trained to conduct the operations. He rewired the severed nerves to control some of the muscles in Zac's thigh that would be used less frequently in the absence of his lower leg. Within just a few months of the amputation, those nerves had recovered from the shock of the injury and began to regenerate and carry electrical impulses. When Zac thought about flexing his fight foot in a specific way, the rerouted nerve endings would consistently cause a distinctive contraction in his hamstring. When compared with prosthetics that were not able to "read" the intent of their wearers, the robotic leg programmed to follow Zac's commands reduced the kinds of errors that cause unnatural movements, discomfort and falls by as much as 44 percent, according to The New England Journal of Medicine. (Source:http://www.orthop.washington.edu/?q=bionic-leg-is-controlled-by-brain-power-article-in-la-times-featuring-dr-douglas-smith.html)
Doug Smith, MD, Orthopedic Surgeon, Harborview/UW Medicine, talks about a new type of prosthetic.
Let's talk about the bionic leg first. What made Zac special and what did you have to do different?
Dr. Smith: Zac is a very unique young man. He had a horrible motorcycle accident and had a horrible knee injury. His ligaments all torn, the blood vessel tore, a lot of the muscle that bypasses the knee was all torn. He had initial attempts to save his leg. They did a vascular repair, but the muscle damage was extensive and if we had continued on the salvage pathway, the muscle that was dying would have been overwhelming and would've actually been life threatening. The difficult decision was made, boy this was back in July of 09 when he had his accident, that an amputation was needed and we had talked to him and did the initial open amputation. Traditionally in leg prosthetics, nerve management is identifying the nerves and then just shortening them so that the nerves are not near the end of the amputation, near where there are a lot of excessive pressures from the socket and the fitting.
Is that when the nerves aren't short enough? Is that where a lot of the ghost pain you hear of comes from?
Dr. Smith: Well, the whole concept of phantom pain I think is the computers that run our limbs, our arms, our legs, is our brain; and the brain is still there and the nerves that go from the brain to the part that's amputated are still there and they're trying to talk. They're trying to connect to what's not there anymore. Your brain is struggling to figure out what these signals mean. Patients definitely have a sense that the parts gone. There is a phantom feeling that the part's still there and then there is unfortunately these jolts or zingers of pain that a lot of people would call the phantom pains and both of those phenomenon happen. We hope that with improved nerve management that that might be less, but it's still a problem that amputees face.
What is an open amputation?
Dr. Smith: Zac, he had an open amputation, meaning that the part that was severely damaged is removed. We wanted one more surgery to wash, clean up, debride, and then finalize everything where we really do the final management of the muscles and the bone. We do the final management of the nerves and blood vessels and we really sew things up with the hope that they will heal and not get infected. Many people with trauma will have two or three surgeries before their final or definitive amputation. Zac had an open amputation and traditionally we do very standard nerve management in leg amputees and most of our work towards this evolving concept of newer nerve management has been an arm amputee primarily to try and get our thoughts to the prosthetic devices.
What's that risk for him to not dead end it? Does it cause him more pain in the short term?
Dr. Smith: Well, the surgery is a little longer and we have to go kind of upstream. We have to make our incisions higher up his leg to go to areas that weren't initially involved in his trauma to actually get the nerves to healthy muscle. It's a little longer surgery; it's a little more dissection; a little more risk, not overwhelming, and he really wanted that done, so we went ahead and actually transferred his nerves. I think he was educated enough to understand the pluses and minuses, and so, what we do is actually take a nerve that would go to your lower leg that was not involved and at that point in time you're sciatic nerve is split into two.
There is a peroneal portion of your nerve, which is really involved in brining your ankle and your toes up or your foot kind of out to the side and the tibial part of the nerve which is involved in bringing your foot down like you're stepping on the gas. The peroneal portion, we transferred to a bit of muscle on the lateral hamstrings, meaning the outside of his distal thigh and we first find a bit of that muscle where one of the nerves going into it is directing it what to do and your hamstrings really work to stabilize your hip and bend your knee. We remove that nerve, so all of a sudden now you have some muscle that doesn't have a communication to it, and we put a nerve onto it that grows into the muscle, arborizes and now connects that bit of muscle to your brain, but with different thoughts. Now that bit of muscle instead of firing when you think about bending your knee, it would fire when you think about raising your ankle. Similarly the other nerve, the tibial nerve, we put on the medial side so again, medial hamstrings or muscles that typically work to stabilize your hip and bend your knee, but that bit of muscle, we took that nerve away that directs it to do that and put a nerve on it that would direct it to fire when you're thinking about bringing your foot down like stepping on the gas.
With Zac, he didn't require anymore surgeries. He went through a lot of traditional prosthetic fitting, and his unique circumstance is now he has the ability to give muscle signals, but there was no prosthetic device that could yet talk to what he had. I'm very fortunate and blessed; I've known Dr. Kuiken in Chicago for probably 20 years now, and Dr. Kuiken and the team at Northwestern were some of the first people to really kind of start moving forward with these nerve transfers and I've been working with them for quite a while. We had a conversation that they were hoping to start doing nerve transfers in legs as we had been their group and our group doing in arms and I said well actually, we have a young man that we've already done it on because he asked for it; and he was like really I gotta talk to this guy. Interestingly, Zac became the first person in that research group, because they were designing the software to read the signals from the muscle and they had a lot of funding from federal and military and veteran programs to help advance prototype limbs that could interpret these signals. Their research got jump started because they already had a patient who had had the surgery; because the patient had asked for the surgery; because he read on the Internet what we were doing in arms. Zac kind of started the whole thing from his research and what he wanted.
Is this something that you think in a few years will be how amputees will go?
Dr. Smith: I mean there are always a lot of different reasons for amputation. I think young people with trauma, a lot of this nerve management, the risks and benefits make sense. For people that have a lot of infection, unfortunately people have a lot of vascular disease, or some of the other situations that lead to amputation, the extra work probably puts them at a higher risk of infections or problems. For many of our young injured people, I think this evolving nerve management has some real benefits. The first benefit is the one that we've learned from arms that you're giving a way for our thoughts to talk to bits of muscle that are remaining to allow prosthetic devices to do new things that they could never do before. For Zac, most people who have an amputation at or above the knee have no way to get the thoughts of moving your ankle up or down to the prosthetic device. If you have the nerve transfers, now you have bits of muscle that can respond to those thoughts and then you can have a prosthetic device that actually works according to your thoughts. I think that was kind of huge that we are moving in that direction for leg prosthetics as well as arm prosthetics.
Okay, so let's talk about nerve transfer. How are you doing it with arms and what would we see if we see a patient and how is that different?
Dr. Smith: I was part of the team initially that was trying to understand how to do this. If someone has an amputation in their forearm, they still have some of these forearm muscles that fire when you think about closing your hand; the remaining parts of those muscles fire when you think about opening your hand; these muscles fire. So someone with an amputation below the elbow doesn't really need nerve transfers to get thoughts to the device. We can put sensors over that muscle and read when you're thinking about closing your hand; and make an electronic prosthesis do it. If however, you lose your arm above the elbow, you have signals from biceps and triceps that control elbow up and elbow down, but when your brain says close your hand, there is no more close your hand muscles left. So you think hard as you want about closing your hand and there is nothing that fires; there is nothing that moves; there is nothing we can read to talk to an electronic device. So we have two biceps which are pretty amazing and you can keep one of them with its normal nerve, so it fires when you think about elbow up. If you take the nerve off of the other one, and shorten that nerve, and then put the nerve that used to go to close your hand on that biceps, within 2, 3 months, the nerve grows in, reinnervates the muscle, and starts talking to that muscle with a new thought. Now, one of your biceps fires when you think elbow up; the other one fires when you think close your hand. Now you have a whole new signal to run a hand on electronic device, and in the back, we can actually do a transfer to the triceps with the nerve that used to open your hand. A traditional above elbow amputee would only have two signals; elbow up and elbow down. They would have to really do a convoluted mechanism that doesn't make sense to try and get the hand to open and close. We took a two signal arm and made it a four signal arm and now they have elbow up, elbow down, and hand open, hand close. We've given them a way to get those thoughts…so we've given them four signals now, so they have the two signals the normal above elbow amputate has elbow up and down, but now they have two new signals, which when they think about hand open and hand close, bits of muscle fire; our sensors can read that and make the electronic device do that. We have now, arm amputees above the elbow that can control that. As you can imagine, if people lose their arm all the way up to the shoulder, they don't even have elbow up, elbow down, hand open, hand close; they have no real active signals, but fortunately, we have muscle on our chest wall, our pectoralis muscles that we can reinnervate and so we can give people that had no real signals, now we can give them elbow up, elbow down, hand open, hand close.
So nerves can be put any other parts of your body and learn new ways to do things?
Dr. Smith: Well, interestingly they don't need to learn anything new, because that nerve started at a part of your brain that had a thought. The nerve that used to do hand close, just dead ended. Now, we put that nerve on some muscle and so it has something to talk to. It doesn't actually have to learn anything new. You don't have to have a new thought. An above elbow amputee used to think hand close and nothing happened. Now, they think hand close and a muscle fires, and that muscle can talk to our electronic devices to make actually the hand close. It's actually not relearning; it's natural. Instead of the nerve dead ending, it now communicates with a tissue, muscle, which we can use to interface with our electronics.
Do you do these nerve transfers with amputations?
Dr. Smith: When it's safe with arm amputees, we are pretty much doing it routinely now for arm amputees, if they don't have overwhelming infection, have actually muscle that can do that, and if the nerves are intact.
And the only time you don't do it, is when?
Dr. Smith: Severe infections, massive zone of injury where the tissues are just too damaged. We are doing it in arm amputees probably half to 2/3 of the time now.
Where do you see this going?
Dr. Smith: I think, the first thing is that we're trying to understand is for a long time, traditional nerve management was just shortening the nerves. We are learning that potentially doing nerve transfers to keep the nerves physiologic, to keep them working talking to muscle, definitely has some benefits; one is getting thoughts to devices, but interestingly there is a strong suspicion that these people might have less pain. Traditionally when you just cut a nerve it forms a very tender lump of nerve endings and scar that's called a neuroma. When you do a transfer, there is less neuromas. There is potentially less neuroma pain. We hope people have less pain. We definitely know that they get more signals and ability to work with more modern prosthetics. Traditionally leg prosthetics are not electronic. There are some things that leg prosthetics or electronics adjust the mechanical motion, but having the ability now to get more thoughts to devices is really spawning a lot of people to say what if we could take what we've learned in arm prosthetics and actually give leg prosthetics motors and functions that connect to our thoughts.
Would this ever end up with feeling prosthetics?
Dr. Smith: That's a great question because when the nerves ingrown, it's not just the motor fibers of the nerves that direct the muscle that ingrows, but sensory fibers ingrown. When people rub a muscle that's been reinnervated, they actually get a sense in the part that's gone. They actually are getting feeling in the muscles so there might be a way and there's people working on it now to get some sensory feedback, back upstream to the brain in a better way than happens now.
Is it just a real nerve sitting on the sensor?
Dr. Smith: Yeah, the interesting part is how do we connect with machines and some people call it a man machine interface, other people have talked about would we ever actually get nerves to grow into machines, currently we have to talk to machines in some way; whether it's mechanical, we move little switches; whether we have a sensor that reads an electrical current in a muscle. There are people that have put skull caps on people trying to read the brain waves and make our electronics work, and that is working to a degree. There are other people wrapping coils around nerves to get the signal that comes down a nerve to go to electronics. Currently, the best way we have to talk to our electronics is through muscle. When muscle moves according to thoughts, we can, we can read how fast it's contracting, how strong it's contracting, whether it's contracting or relaxing, we can get a lot of information out of what that muscle does and then use that information to kind of interpret the thoughts and make our electronics work. At this moment, the best way to talk to our electronics is through transferring nerves to muscles to get those thoughts into a bit of muscle we can talk to. In the future, we may well be able to read brainwaves; we may well be able to read the electronic current of a nerve, but right now, we can't.
How does the machine read it though? So you have your arm on, how does it read?
Dr. Smith: You're required to actually have a sensor over the muscle that's firing and when a muscle fires, it generates wave patterns of electric currents, EMG signals. The sensor sends those to a computer that interprets the signal to decide how strong a contraction, how fast a contraction, was it contracting or relaxing, but it can interpret a lot of information that it can then use to make the prosthesis move in unique ways.
And that sensor is on the outside of the skin?
Dr. Smith: Currently, the sensor is on the outside. There are people looking at tattooing sensors into your skin so they are there all the time. There are other people that have invented little sensors that go into the muscle that might be a little more accurate, so you would eventually have something implanted. There are people looking at all kinds of sensors to actually get the whole concept, which are thoughts through some body tissue to electronics and all of those interfaces are improving rapidly, but right now, the best is getting nerves to muscle and listening to that muscle.
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