Prosthetics and the Violin

Dr. Gregory A. Dumanian and colleagues investigated the possibility of reinnervating neural connections for the enhanced use of prosthetic limbs, more specifically, arms. The motivation behind this research resulted from the lack of prosthetic movement due to physical and technological limitations. In one of the studies, a female participant with a left arm amputation went under surgery to isolate and relocate the ulnar, median, distal radial, and musculocutaneous nerves; the same nerves that were severed during the amputation. Before the reinnervation, the nerves were in one large bundle with nothing to pass an action potential to. These free nerve endings may hint to an answer a part of the phantom limb phenomenon. During the surgery, the one bundle was separated into four distinct bundles. The ipsilateral pectoral muscle was separated into four muscles, in order to assign a nerve bundle with a separate pectoral muscle. This process was termed Targeted Muscle Reinnervation (TMR) by Dr. Dumanian. In his presentation, he demonstrated the results of TMR in a video comparing the movement of the same prosthetic before and after the surgery. The difference in fluid motion was astonishing, the results showed a promising future in this field of research. The difference in the two movements was the ability to simultaneously move the arm in multiple directions. For instance, before the surgery, the prosthetic was limited to movement in a vertical, horizontal, or diagonal direction at once. After the surgery, the arm was able to move in circular motions if the patient wished. Obviously, this closely resembles the fluid motion that natural joints allow in upper limbs.

The reason behind this difference was because of TMR. The separation of the one disconnected bundle into four bundles allowed the participant to isolate desired movements, which made them “smarter” signals as Dr. Dumanian described them. One could imagine this like a joystick on a video game controller, one input results in one direction of movement, but a combination of joysticks adds more dimensions into a single movement, i.e. bending at the elbow while rotating the arm. In such a manner, the prosthetic sensors have more input signals from the participant to better interpret the desired combination of motions. Of course, the ability to execute complex motions is the motivating force behind prosthetic research. This is so normal arm function can be restored to the patient. Recently, undergraduate students have created a prosthetic arm for a little girl so she can play violin.

In Fairfax, Virginia, undergraduate students of George Mason University were called upon by an alumnus to work on this project. Isabella Nicola, a fifth-grader at a local elementary school, was born without a left hand, and a disformed forearm. Coincidentally, this group of bioengineer majors were on a hunt for a capstone project to complete for graduation, so this was the perfect opportunity to help both parties. The final prosthetic that the group constructed was made by a 3-D printer, weighing at about 11 ounces. She could play the violin much better thanks to the new arm. They even gave her extra attachments so she can grip a handlebar to ride a bike. The technology used in the prosthetic was not completely described, but it is evident that the complexity of it was enough to allow Isabella to play the violin. With advancements like Dr. Dumanian’s findings, complex prosthetics will be much more common than an undergraduate project taken last second. Hopefully, it will be properly funded and promoted to the point that complexity is not an issue.

    

References:

https://www.nytimes.com/aponline/2017/04/21/us/ap-us-girl-violin-prosthetic.html?_r=0

http://www.sfgate.com/news/education/article/Prosthetic-arm-designed-by-undergrads-lets-girl-11091145.php 
https://www.youtube.com/embed/TJaGzXle8uA?ecver=2