A US study shows that a new type of surgery called pattern recognition technique with targeted muscle reinnervation (TMR) appears to help patients with amputations to gain better control of prosthetic arms.
The research comes from the Rehabilitation Institute of Chicago (RIC) and is published as a paper in the February 11 issue of JAMA, Journal of the American Medical Association.
Current technology for patients who have had an arm amputated are body-powered: the prosthetic arm captures remaining shoulder motion with a harness and transfers it through a cable to enable the patient to operate the hand, wrist or elbow. This only partially restores the ability to use an arm and hand because the patient can’t operate more than one joint at a time, wrote the authors in their background information.
The challenge is to restore the nerve-control that is lost when the arm is amputated. This is where TMR comes in: it transfers remaining arm nerves to chest or upper arm muscles that don’t work any more because the limb is no longer there, and special prostheses can use electromyogram (EMG) signals (electrical signals used in muscle contraction) from the residual limb muscles to control motorized arm joints.
The idea is that once nerve function is restored, the TMR reinnervated muscles give the right EMG signals to control the elbow, wrist and hand of the artificial arm. However, what is somewhat new territory is whether the reinnervated muscles can give stable and accurate EMG signals that enable the patient to control the artificial arm in “real time”: can they just think what they want the arm to do and it responds almost immediately, with the right movement?
For the study, which took place between January 2007 and January 2008, Dr Todd A Kuiken, who is director of the RIC Center for Bionic Medicine, and colleagues, assessed the performance of five participants with upper limb amputation who had had TMR surgery. They also assessed five participants who did not have amputations for comparison (the controls).
The researchers asked the participants to move their arm in various ways, and assessed their ability to control their arm and speed of movement selection and movement completion, as well as their ability to complete the movement.
The results showed that:
- The average motion selection times for elbow and wrist movements such as flexing and extending the elbow, rotating, flexing and extending the wrist, was 0.22 seconds for TMR participants and 0.16 seconds for the controls.
- The average motion completion rate for elbow and wrist movements was high: 96.3 per cent for TMR participants and 100 per cent for controls.
- The average motion completion times for elbow and wrist was 1.29 seconds for TMR participants and 1.08 seconds for the controls.
- Hand grasps took longer to complete than arm movements for both groups.
- The average motion completion time for hand grasps was 1.54 seconds for TMR participants and 1.26 seconds for the controls.
- Three of the TMR participants also showed they could use the control system in advanced prostheses, including motorized shoulders, elbows, wrists and hands.
The researchers concluded that:
“These results suggest that reinnervated muscles can produce sufficient EMG information for real-time control of advanced artificial arms.”
They wrote that these early trials show how TMR can be used to help patients control complex multifunction prostheses. Feasibility has been established, but more research and development is needed before trials can start. They explained that:
“The prosthetic arms tested in this study performed very well as early prototypes. Further improvements are needed and have been planned, including reducing the size and weight and increasing the robustness of these advanced prostheses.”
Kuiken said in a separate press statement that:
“The use of pattern-recognition control is an exciting advancement for patients with arm amputations.”
“It will allow us to decode more neural information from the patients providing enhanced, more natural operation of their prostheses,” he added.
40-year old Amanda Kitts lost her left arm below the shoulder in a car accident in 2006. She underwent TMR at RIC, where they rewired the nerves that once sent signals to her left arm and hand to skin and muscle in what was left of her bicep. She was then fitted with a myoelectric prosthetic arm that went over her residual limb: this sends electrical signals to the arm, so that when Kitts thinks about moving her arm or hand, the prosthetic arm or hand moves.
Kitts, who took part in the JAMA study, said:
“I was amazed at the level of hand function and how fast I was able to control the arm and hand.”
“I was able to pick up a penny off the table and could catch an object in motion like a checker that was rolling across the table. It’s really amazing to be able to just think about it and have my prosthetic move so quick,” she added.
Kitts was one of the three TMR patients in the study who used the advanced prostheses. These were developed by John Hopkins University Applied Physics Lab (JHUAPL) and Deka Research, Inc as part of the Defense Advanced Research Projects Agency (DARPA) Revolutionizing Prosthetics Program that was launched in 2006.
“Targeted Muscle Reinnervation for Real-time Myoelectric Control of Multifunction Artificial Arms.”
Todd A. Kuiken; Guanglin Li; Blair A. Lock; Robert D. Lipschutz; Laura A. Miller; Kathy A. Stubblefield; Kevin B. Englehart.
JAMA Vol. 301 No. 6, pp 619-628, February 11, 2009.
Sources: Journal abstract, JAMA news release, Rehabilitation Institute of Chicago.
Written by: Catharine Paddock, PhD