Targeted Muscle Reinnervation Increases Prosthetic BMI

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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.

VWN Virtual Dictionary : Targeted Muscle Re-Innervation

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 arms.

"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 human ability."

Amanda Kitts Operates a Bionic Arm with her Brain as part of JAMA study (no sound)