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The Rehabilitation Institute of Chicago has been quietly working to increase
the fidelity of prosthetic arm haptic controls. One of the studies underway,
was released for public viewing on February 10th, 2009. The Journal of the American
Medical Association study looked at targeted muscle reinnervation to see if
it did indeed have as much success as studies conducted by those with a vested
interest in a positive result, have found.
Targeted muscle re-innervation is a method of allowing an artificial
or virtual arm, to respond as an organic arm would to sub-conscious thought
patterns. TMR works by rewiring nerve endings.
Surgeons cut the nerves serving chest muscles that once helped support
and move the missing limb. These are, after all, no-longer needed. Then
they separate out the motor nerves in the arm stump that used to control
the patient's arm and connect them to the chest muscle instead. This gives
the nerves ample blood supply to keep working. When the patient goes to
move their arm or hand, the nerves in the chest muscle fire, sending the
signal to the arm, and the signal is picked up, and deciphered
by a sensor which tells the prosthetic how to move.
The JAMA study has agreed with previous findings, discovering that the transfer
of residual arm nerves to alternative muscle sites does indeed work to activate
and control prosthetic arms, to great benefit of the patient.
From the study:
The TMR patients were able to repeatedly perform 10 different elbow, wrist,
and hand motions with the virtual prosthetic arm. For these patients, the
mean motion selection and motion completion times for elbow and wrist movements
were 0.22 seconds (SD, 0.06) and 1.29 seconds (SD, 0.15), respectively. These
times were 0.06 seconds and 0.21 seconds longer than the mean times for control
participants. For TMR patients, the mean motion selection and motion completion
times for hand-grasp patterns were 0.38 seconds (SD, 0.12) and 1.54 seconds
(SD, 0.27), respectively. These patients successfully completed a mean of
96.3% (SD, 3.8) of elbow and wrist movements and 86.9% (SD, 13.9) of hand
movements within 5 seconds, compared with 100% (SD, 0) and 96.7% (SD, 4.7)
completed by controls. Three of the patients were able to demonstrate the
use of this control system in advanced prostheses, including motorized shoulders,
elbows, wrists, and hands.
Conclusion These results suggest that reinnervated muscles can
produce sufficient EMG information for real-time control of advanced artificial
"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,"
said Todd Kuiken, MD, PhD, director of the RIC Center for Bionic Medicine. "This
neural interface, used in combination with DARPA's new sophisticated prosthetics,
is creating better patient independence and supporting RIC's vision to advance
Amanda Kitts Operates a Bionic Arm with her Brain as part of JAMA study (no