Nerve Reapplication in Amputee Rehabilitation

 Nerve Reapplication in Amputee Rehabilitation

Prosthetics have been in common use for an extremely long time, starting very rudimentarily, such as the peg leg. In the ages gone by, huge developments in the technology of the artificial limb have occurred. While there’s no claim that prosthetics are just as accurate as the natural limb, recent advancements have gotten far closer than ever anticipated in the past.

In the research article “Robotic Leg Control with EMG Decoding in an Amputee with Nerve Transfers” by Levi J. Hargrove et al, a case study is addressed of a man who lost his knee and below due to a motorcycle accident. During the amputation surgery, medical doctors completed two nerve transfers to prevent the formation of neuromas -- benign tumors of nerve tissue, also known as pinched nerves -- which is standard practice in amputation surgeries today, whether the limb lost is an arm or leg. After recovery from his surgery, the patient was able to ‘move his foot’, which tensed certain parts of his remaining thigh, due to the transferred nerves naturally reinnervating themselves into the thigh muscles during the healing process. In the study completed from 2010 to 2012, after he healed from amputation, researchers used electromyography (EMG) to gather and process the nerve signals present in his thigh. Differentiation between natural nervation and surgical reinnervation was completed through a virtual environment with direct tracking of muscles known to be naturally innervated, and those known to be surgically innervated. The virtual simulation contained a pattern-recognition system that allowed the patient’s data to be compared with other amputees’ who did not receive targeted muscle reinnervation (TMR) during their amputations. The results of this comparison showed that reinnervation decreased the inaccuracy of the pattern recognition system by up to 44%, a drastic and impressive drop in error. The major importance of this error decrease shows itself in the use of robotic prostheses. The EMG data from the residual limb in addition to the mechanical sensors within the prosthetic leg allowed the error rate of movement classification to drop from 12.9% to 1.8%. Even when demonstrated in a single example, the benefit of TMR is extremely noticeable for amputees in need of advanced prosthetics.

Another article, released in 2020 from the University of Michigan called “‘It’s like you have a hand again’: An ultra-precise mind-controlled prosthetic” proves the possibility and value of TMR for patients with residual arms, rather than residual legs. Because of how much smaller, more delicate, and more advanced the movement of the hand is, the exact methods used previously are not quite as effective. So, the team at UMichigan wrapped small muscle grafts around the residual nerve endings in patients arms, called regenerative peripheral nerve interfaces (RPNIs). These RPNIs not only prevent neuroma formation, but also act as amplifiers for the signals from the nerve endings. There was also the implantation of electrodes with the RPNIs, that allow a connected prosthetic hand to receive and utilize the nerve signals in real time, returning advanced use of the fingers to the amputees. 

The advancement of prosthesis has been ongoing for ages-- but seeing valuable progress in the span of ten years is a very good sign. With the quick advancement of technology in our world today, it’s nerve wracking to think that maybe some of the valuable uses of technology may not have been able to keep up-- but this has! TMR and RPNI are both huge accomplishments for neuroscientists and roboticists. As our world continues, maybe we will even see innervation into permanent prosthetics for amputees.

Sources

Casal Moore, Nicole. “‘It’s Like You Have a Hand Again’: An Ultra-precise Mind-controlled Prosthetic.” University of Michigan News, 10 Mar. 2020, news.umich.edu/its-like-you-have-a-hand-again-an-ultra-precise-mind-controlled-prosthetic.

Hargrove, Levi J., et al. “Robotic Leg Control With EMG Decoding in an Amputee With Nerve Transfers.” The New England Journal of Medicine, vol. 369, no. 13, Sept. 2013, pp. 1237–42, doi:10.1056/nejmoa1300126.