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To learn more about upper extremity prosthetics, AAOS Now spoke with Douglas T. Hutchinson, MD, author of “The Quest for the Bionic Arm,” appearing in the June issue of the Journal of the AAOS. Dr. Hutchinson is associate professor of orthopaedics and adjunct professor of bioengineering at the University of Utah where he has been involved in upper extremity prosthetic research for 15 years.

AAOS Now

Published 6/1/2014
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Maureen Leahy

Perfecting the Artificial Arm

Research focuses on creating prosthesis with full motor and sensory function

Due to wounds sustained during military operations in Iraq and Afghanistan, more than 1,600 American service members have required extremity amputations, 14 percent of which were upper limb. However, current body-operated and myoelectric upper extremity prosthetics lack the sensation, durability, and function that patients desire.

AAOS Now: How have upper extremity prosthetics evolved over the years? What is the current state of the technology?

Dr. Hutchinson: Both body-operated and myoelectric prostheses have been available for quite some time without many significant changes. For example, most patients still use a body-operated hook that was invented during the Civil War and refined during World Wars I and II.

First developed 50 years ago, myoelectric prostheses allow residual muscles to act as natural batteries that create transcutaneous signals to control the movement of the terminal device. However, the muscles used most often are the biceps and triceps, which do not naturally translate to the opening and closing of the hand. All types of prostheses used clinically today also employ inefficient, uncomfortable, hot, and often joint-eliminating sockets to interface with the amputated arm.

Research is currently focused on creating a complete prosthesis with full motor and sensory function that will provide amputees with a near-normal human arm. Specific metrics include increased durability and strength, two-point discrimination, pressure sensitivity, and 4 degrees of freedom of motion in each digit, all in a waterproof form. Several new generation prostheses have already been developed, but their ability to interface with the nervous system and to be directly implanted to the bone has not yet been fully realized.

AAOS Now: What must happen before such a device becomes reality?

Dr. Hutchinson: Several challenges must be overcome before a functional, so-called bionic arm is a reality. For one, osseous integration—direct implantation to bone—will contribute to a more comfortable, lightweight, and stronger prosthesis. It will also provide proprioceptive feedback through the bone, giving the user the sense that the prosthetic arm is part of his or her body.

Although prosthetic osseous integration has been used successfully in dental reconstruction, translating this technology to leg and arm prostheses has been difficult, secondary to infection risks. If advances in controlling infection of osseous-integrated prostheses can be achieved by manipulating the skin interface, the use of such devices will likely increase.

In addition to improving degrees of freedom and sensation, better inputs are required to provide maximum function. Categories of input include muscle, central nervous system, and peripheral nerve. Acquiring signals via muscle or nerve inputs will require either a reliable wireless device or direct wiring through an osseous-integrated implant; percutaneous wires will not be sufficiently durable.

With targeted reinnervation—a surgical technique developed by researchers at the Rehabilitation Institute of Chicago—residual nerves of an amputated limb are transferred to a chest wall muscle or a spared distal muscle to control the prosthesis in a more natural way.

To learn more about upper extremity prosthetics, AAOS Now spoke with Douglas T. Hutchinson, MD, author of “The Quest for the Bionic Arm,” appearing in the June issue of the Journal of the AAOS. Dr. Hutchinson is associate professor of orthopaedics and adjunct professor of bioengineering at the University of Utah where he has been involved in upper extremity prosthetic research for 15 years.
Intraoperative photograph of a nerve cuff in vivo, demonstrating the size of the cuff in centimeters (Reproduced with permission from Weir RF, Troyk PR, DeMichele GA, Kerns DA, Schorsch JF, Maas H: Implantable myoelectric sensors (IMESs) for intramuscular electromyogram recording. IEEE Trans Biomed Eng 2009;56[1]:159-171.)

How best to use the patients’ nervous system as an interface for prosthetic electrical inputs has yet to be determined. Two possibilities include being able to tap directly into the central nervous system via open brain surgery, and another less invasive method utilizing the peripheral nerves of the amputated arm.

AAOS Now: How does transplantation affect bionic arm research?

Dr. Hutchinson: Arm transplantation and all of the science involved will benefit many patients in the future. However, I believe the advances in prosthetics will eventually make the results of transplantation obsolete and, similar to heroic attempts at proximal level replantation, transplantations will no longer be performed. Advances in both areas are scientific positives that will help well beyond their intentions. It’s fair to say, however, that advances in one could easily affect advances in the other.

AAOS Now: What implications will upper extremity prosthetic advances have for orthopaedic surgeons?

Dr. Hutchinson: Hand surgeons who perform peripheral nerve surgery will obviously be part of the team that places these devices into patients. But perhaps more relevant will be the different way we treat severe near or complete amputations. We will need to preserve muscles and nerves even more than we already do to make later reconstruction more successful.

AAOS Now: How will prostheses further evolve in the future?

Dr. Hutchinson: I believe we will be able to make artificial arms function better than the injured arm that may be salvageable today. We currently spend a lot of time, energy, and money saving hands and arms that have a poor prognosis because the alternative—an amputation and an insensate myoelectric prosthesis attached by a socket—is even worse. As we improve the prosthesis, the options for patients with severely injured upper extremities will increase. Similar to the present situation with the lower extremity, a prosthetic may well become a better answer for many patients with crush injuries.

Disclosure information: Dr. Hutchinson reports no conflicts.

Maureen Leahy is assistant managing editor of AAOS Now. She can be reached at leahy@aaos.org

JAAOS article
The Quest for the Bionic Arm

Bottom Line

  • Research is currently focused on creating a complete prosthesis with full motor and sensory function that will provide amputees with a near-normal human arm.
  • Several challenges—including osseous integration and better input signaling from bone, muscle, and nerves—must be overcome before a functional bionic arm becomes a reality.
  • As they develop, upper extremity prostheses may supplant transplantation and limb salvage to become the desired treatment in cases of crush injuries.