The Doctor behind the latest orthopedic surgical procedure explains history behind the technique of building bionic hands.
Last month, a team of surgeons in Vienna reported on their experience replacing injured hands in three patients with a mind-controlled prosthesis dubbed a “bionic hand.” In this article, the team leader tells some of the backstory.
For about 25 years, I have been dealing with patients with all sorts of nerve injuries. The most devastating are those whose brachial plexus has been severely injured. My very first teacher in nerve surgery, Prof. Hanno Millesi, taught me the art of nerve reconstruction, and even in the worst-case scenarios, he seemed to have a solution, whether these were anatomical reconstructions using nerve grafts, intra- and extraplexual nerve transfers, or secondary reconstructions using tendon transfers, tenodesis, or arthrodesis.
However, with time I realized that there is an unfortunate group of patients in whom, for various reasons, biologic reconstructions would not result in any meaningful hand function. The hands of these patients presented a biologic wasteland, beyond the hope of ever being repaired given existing reconstructive methods.
Some years later I got involved in a research project to improve control mechanisms in prosthetic limbs. The research and development department of the prosthetic company was just a few subway stops away from the university campus, and thus an exciting collaboration developed. Quickly, I realized that mechatronic hands have tremendous capabilities, and if the biotechnological interface could be improved, could indeed provide substantial help to the patients who had little or no hand function.
A normal upper extremity is supplied with about 250,000 nerve fibers with about 10% being dedicated to moving the arm and hand. If these are either torn out of the spinal cord or damaged somewhere along the way, the arm and hand will become paralyzed. Even if some motor fibers will eventually make it to the forearm and hand after reconstructive surgery, in many cases the muscles there have undergone irreversible atrophy and fibrosis.
Thus these regenerated nerve fibers will not be able to provide enough power to move a stiff hand. But even then, they may still transmit signals that are intuitive and intimately connected with hand movement.
Since the muscles in the forearm had withered irreversibly, and the language and signal intensity of these nerves could not be read by electronic sensors, we transplanted fresh muscle from other parts of the body as a translator and bioamplifier of these faint nerve signals. Once these axons made successful contact and the muscle started to contract, patients began a process called TechNeuroRehabilitation to train their brain.
Since some patients had not thought of controlling their hand for many years, the corresponding central motor centers also needed to be strengthened. This process was mediated by virtual reality or with real, but temporary, prosthetic means. This alone provided a tremendous motivation for the patients, as they realized that they could, in fact, move a hand with just the power of thought alone.
When Milo came to my office in the fall of 2009 for a follow-up examination after a global plexus injury about 8 years earlier and a number of reconstructive surgeries, he had good shoulder and elbow function but very poor forearm and hand function. He asked what else could be done to improve this poor state of affairs.
As luck would have it, we had just started to begin the exploration of the bionic reconstruction concept, and thus I invited him to come to our lab to see whether we could identify some myoelectric signals that could be useful for prosthetic control. And indeed, even that day we were able to identify two distinct signals which he could use to control a virtual hand.
A few months later, and after a considerable amount of discussion and hybrid hand training, both Milo and myself were convinced that a prosthetic hand replacement was the right path to pursue.
Today, 5 years later, he tells me that losing his hand was beyond a shadow of a doubt the right decision. I saw him again just a few days ago about 15 years after the initial accident and was, once more, thankful for having the opportunity of bionic extremity reconstruction.
Originally published in Med Page Today
Written by Oskar C. Aszmann MD