TMR Surgery

The main reason for Kuiken and his partners to develop the TMR was to enable patients to have a more intuitive and natural movement of their prosthetic. The current available prosthetic technology makes use of different muscles to command a bionic limb. As an example for the current system, if a patient has an amputation passed the elbow, he/she will have to be trained with the prosthetic to learn how to control it. The required contractions to move a wrist, for example, would be to flex the biceps. This causes the patient’s interaction with the prosthetic to be slow, jerky, and unnatural. The following short video is part of the TED talk mentioned in the previous post. Here you can see that the patient, Jesse Sullivan, who had both arms amputated, moves almost twice as fast after the TMR surgery. It is also worthwhile to mention that he had been wearing the original prosthesis for 40 months, while the other one was only worn for 2 months, showing the extreme difference between the two.

Original (wearing for 20 months) VS Nerve Transfer (wearing for 2 months)

In Sullivan’s case, he had a shoulder disarticulation on both arms due to trauma, which resulted in a surgical amputation. This means that his entire arm was separated from the shoulder joint. In more technical terms, the humerus bone was removed from the scapula and the clavicle, which are respectively the shoulder blade and the collar bone. The target muscles for Sullivan’s reinnervation were the ones in the pectoral area. As seen on the drawing below, different nerves are assigned different muscle areas, so when rooted, the nerves will control just that area.

Shoulder Disarticulation Drawing

If you recall what I wrote a few lines ago, the objective of this technique is to amplify the signal for improving a myoelectric prosthesis. Now, the unexpected and exciting discovery they made changed the course of the research. If you stop to think about the process that goes on with reinnervated muscles, you will realize that it doesn’t act differently than any other muscle in your body. Your brain simply sends a message through your nerves to your muscles saying “contract” or “extend”, and that’s exactly what was done… so what? So if it works on the path brain-nerve-muscle, shouldn’t it work the same way around? YES, it should and it does! Three months after the patients were submitted under the TMR surgery, they started a series of tests. And when they were touched in their reinnervated muscles, they could feel as if they were being touch in their lost limbs! Not only that, but they could also feel temperature, pressure, and texture as well. This is very exciting because it means that when researchers have the means for it, a fully functional limb that “feels” could be created. An immense drawback to the development of this “perfect” limb would be the absurd cost of such a device. Michael McLoughlin, the lead designer of bionic arms at Johns Hopkins, estimated that the price for a device like these would fall under the cost range of $50,000-$60,000. Although bionics with such a high pricing would be economically unviable for many people, it is usually easier for engineers and researchers to cut down the cost of something that has everything it needs to offer.

The information and pictures on this post were based off the academic paper published by Kuiken and his partners. For further understanding and direct access to the paper, click here.


What are body-powered and myoelectric prosthetics and how do they work?i

There are many types of prosthetics available in the market today for all kinds of disabilities. The type of device that a patient may choose is going to depend on his/her needs and desires. Today I am going to talk about the two main types of mechanical prosthetics that are currently available and how the contrast. These devices are the body-powered, and the myoelectric prosthetics!

Body-powered Prosthetics

As its name indicates, this prosthetic is powered by the patients body. It usually uses the remaining extensions of the patients limb to function the device. They are fairly simple and most of the time make use of wires and bolts. As you can see n the middle picture below, the device sits on the forearm and the remaining part of the patients limb. When the patient bends their hand, the wires you see in the picture work as tendons and make the hand close. This is a very specific application for a body-powered prosthetic, but since each case is different it’s very complicated to mass produce prosthetics. This is one of the reasons why they can be so expensive.

Curtesy of E-nable (Click for website)

Myoelectric Prosthetics:

On the other end of the spectrum from the body-powered devices are the myoelectric prosthetics. They are the current state of the art prosthetic devices and are also known as bionic limbs. The main characteristics of these devices are that they are electronically equipped. They are composed of a motor, a control unit, a battery, and electrodes. The way it works is that the electrodes capture the muscle movement in the patient’s arm, send that information to the control unit, and from there it moves the motor accordingly to the patient’s desire. Some of the problems with these devices are that they are usually heavier than what the patient’s limb would weigh, and they are slow to process commands due to the method utilized to pick up the signals.

Recently, a group of researchers with the hope of improving bionic arms, have experimented with what is called a TMR (Targeted Muscle Reinnervation) surgery. The leader of the research was Todd Kuiken, the director of the Center for Bionics Medicine. This surgery is very promising for the improvement of the the signal amplification through biological means. In a brief summary, this surgery moves the nerve endings that would control the patient’s arm muscles and root these nerves into the patient’s chest muscles. The surgery performed by the researchers was successful and a few very exciting and unexpected discoveries came out of this experiment.

In the next post I’m going to talk a little bit more about the outcome of the surgery, and its discoveries. I’m also going to explain the TMR surgery in a little more depth . Click here if you would like to watch Kuiken’s TED talk A prosthetic arm that “feels”  and get a head start on the subject of the upcoming post.

The challenge of being physically disabled

I am sure all of you have seen a person with a physical disability before, but have you ever thought how your life would be in their place? Have you ever thought about how that disability would keep you from going on with your current and future plans? Imagine how woeful it would be to give birth and not be able to carry your own child, how depressing it would be to not be capable of teaching you son how to play baseball, or how sad it would be to a be a brother and play all sorts of games, but have your sibling just watch. It can be painful to imagine, but if you do, you will realize how hard all of that would impact on your life. According to the U.S. Census Bureau, in 2012, about 19.9 million of Americans above the age of 15 have some kind of upper body physical disability, and 30.6 million suffer with lower body disability. These numbers are equivalent to 20.8% of the entire American population. This percentage could be extremely reduced if more time was spent on prosthetic research to make them cheaper and more efficient, allowing the 1/5 of the American population to have a normal life.