Revolutionizing Prosthetics

The Challenges of Current Prosthetics

             The problem with existing prosthetics is that, along with visual feedback, they are mostly controlled with the residual muscles and nerves that are left in the amputated limb. Some specific challenges of operating a prosthetic, with the remaining and sometimes mangled nerves, are that they allow for a very limited range of motion. Most often movements can be robotic and slow. Additionally, and most importantly, current prosthetics lacks sensory feedback. Moving the amputated limb (in this case will assume the amputated limb is a hand) does not have the natural intuitive feel for motor function,  and on top of that a plastic metal based prosthetic does not feel. Thus, scientists have focused their energy on improving this field and the lives of amputees.

            In a recent study at the Rehabilitation Institute of Chicago, Kuiken et al. (2007) conducted an investigation that used targeted muscle reinnervation as a way to improve the function of prosthetic arms. Kuiken and colleagues (2007) developed the targeted muscle reinnervation method as a way to solve some of the difficulties with current prosthetics, and overall increased motor skills for  individuals with amputated limbs

What is TMR?

            To begin with, the goal of this experiment was to develop new motor and sensory signals in the chest as a way to provide sensory feedback for a missing limb. The method used by Kuiken and colleagues (2007) to accomplish this was targeted muscle reinnervation (TMR). This approach transfers functional nerves from the amputated limb and sews them together into a larger group of muscles that are located in the chest. In the case explained by Kuiken et al., the ulnar, median, musculocutaneous, and distal radial nerves were removed from the amputated limb, and places into the pectoral muscles of chest. The neural connections to the brain still exist in the pectoral nerves, but since the distal ends of these nerves are missing (located in the amputated limb), the pectoral muscles remains non-functional.  Think about how difficult it must be to  want to make a fist with your hand but not have any fingers. The neural connections are still there, the forearm muscle will contract but there is no end point  because there is no hand.  With the TMR technique, the motor nerves from the amputated limb are sewn together with the remaining pectoral muscles. The pectoral muscles will act as neural amplifiers for motor control and are necessary for this experiment because they have the established neural connections to the brain.  (Kuiken et al., 2007) Although the TMR method may seem very complex and slightly remind one of Frankenstein, the results for targeted muscle reinnervation have been able to return many fine motor skills to the patient at a rate that is four times faster than the normal prosthetics. This is because the pectoral muscles with the neural connections have been connected to neurons that control fine motor skills. With the attachment of a modified prosthetic, the patient will think about making a fist, the message will travel through the neural pathways to the pectoral muscles, that now have fine motor nerves attached to them, and synapse on specialized electrode located in the prosthetic. The electrode will encode the neural activity into the prosthetic, and the action will terminate with the prosthetic  making a fist.

            Furthermore, a similar but different method used by the investigators was targeted sensory reinnervation (TSR).  The TSR method was done by placing some sensory nerves from the amputated limb in the TMR area. The results showed that TSR also brought back some of the sensations that had been lost such as: pressure, temperate, and texture. (Kuiken et al., 2007) Moreover, the implications of these findings have opened up new doors in the world of prosthetics.  Now that the neural connections have been properly established prosthetics must also be adapted with new myoelectric signaling pathways. In all, it is clear that Kuiken and colleagues (2007) have revolutionized the world of prosthetics, and neuroscience.

New Doors

            Moreover, it is not just scientists at the Rehabilitation Institute of Chicago that are working on improving prosthetics, but also researchers at Case Western Reserve University. In the article, A Prosthetic Hand That Can Feel, by Andrea Tsai and Alexandra Sifferlin, the journalists explain the technological advancements being done at Case Western Reserve University.

            The obvious goal for these scientists is to develop a prosthetic hand that can feel, and has a natural intuitive sensation to it. Similar to the Kuiken et al., TSR technique that brought back some sensory sensation, the researchers at Case Western have worked on a sensory approach of their own.  In the Case Western approach the prosthetic hand is equipped with specialized sensors that measure variations of pressure.  The sensors convert the mechanical stimulus into a neural message that it sent through wires up to electrodes that have been surgically implanted in forearm or upper arm (distal end of the body where limb was amputated). The electrodes  encoded message into a neural message that is transmitted to healthy neurons with established connections,  that send the message to the brain. (Tsai & Sifferlin 2015)

Compare and Contrast

            Although very similar  Kuiken et al., and the researchers at Case Western seem to be approaching the problem of prosthetics from different angle. Kuiken and colleagues were focused on motor function that is controlled from the brain to the hand. TMR is connecting muscles to muscles, and involves a prosthetic that can transfer the message from the neurons to the hand, so that the prosthetic can execute the command. They also performed TSR, except because the sensory nerves were sewn into the pectoral muscles; the chest is the area that can feel. Think about it this way, poking someone in the chest may feel like to the patient that you are touching his or her right finger. Interestingly enough, the researchers at Case Western are working on a different approach that goes from the prosthetic to the brain instead. Case Western has specialized sensors that encodes the information to electrodes, which transmits the information to neurons and the brain. In the future, the researchers at Case Western hope to create a wireless system for their prosthetic. Wouldn't it be crazy for  patients to control motor movements through the wifi? 

 If only the both approaches could be implemented together this would create a new frontier for the world of prosthetics.

Bibliography:

Kuiken, T. A., Miller, L. A., Lipschutz, R. D., Lock, B. A., Stubblefield, K., Marasco, P. D., Zhou, P., & Dumanian, G. A. (2007). Targeted reinnervation for enhanced prosthetic arm function in a woman with a proximal amputation: a case study. The Lancet Journal, 369, 371-380. doi:10.1016/S0140-6736(07)60193-7.

Tsai, Diane, and Alexandra Sifferlin. "A Prosthetic Hand That Can Feel." Time. Time, 16 Nov. 2015. Web. 01 May 2017.

Images:

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