TMR Surgery Allows for Intuitive Control of an Externally Powered Prosthesis

Targeted muscle reinnervation (TMR) surgery, coupled with a
new externally powered elbow prosthesis called the Dynamic Arm TMR, allows for
simultaneous control of the elbow, hand and wrist joints for upper extremity

TMR surgery, pioneered by Todd Kuiken, MD, PhD, director of the Neural
Engineering Center for Artificial Limbs at the Rehabilitation Institute of
Chicago, requires surgeons to graft residual nerves of the upper extremity onto
targeted muscles that remain in the residual limb. The nerves that controlled
the hand, wrist and elbow movement are then activated in the targeted muscle.
When a person thinks about motioning their arm, they are firing those muscles
and pickup electromyogram signals. The same nerves that gathered signals and
controlled the natural arm, will have the ability to pickup the signals from
the person’s brain and control the joint in the prosthesis.

  Julie Schick
  Julie Schick

In a seperate study released in 2009 by the Journal of the
American Medical Association
, five patients who had undergone TMR
surgery and five control participants without amputation were instructed to
perform various arm movements. Their control of a virtual prosthesis arm was
assessed. According to the study, the average motion completion rates for elbow
and wrist movements were 96.3% for TMR patients, as opposed to 100% for the
control group.

“Because of the electrodes that are on your skin, you are able to
feed those input signals into the hardware,” Julie Schick, CP, OTR/L,
clinical specialist for upper extremity prosthetics at Otto Bock Health Care
told O&P Business News. “Due to new software programming
inside the elbow, the device is able to process all of the signals at the same
time. [The user] is able to have simultaneous control of the elbow, wrist and
hand joints.”

Think about reaching out and shaking a person’s hand. Instead of an
upper extremity amputee individually thinking about moving their elbow joint up
or down, their wrist joint palm up or palm down and then their hand open then
closed, they can think to shake a person’s hand.

“There are a lot of the same technical aspects in the Dynamic Arm
TMR,” Schick said. “But because this has been modified with different
hardware, as well as internal software programming, the Dynamic Arm TMR is a
much different product.”

The Dynamic Arm TMR has the ability to move at various speeds and lift
up to 13 pounds. This allows the user to perform basic tasks with the
prosthesis such as picking up a gallon of milk. The device also features an
automatic forearm balance (AFB). The AFB allows the arm to swing when the
person is walking, as opposed to straight at a person’s side. This is just
a small attribute to the prosthesis that gives the user a more natural feel.

“The arm has the ability to proportionately control the different
joints and components throughout the entire system,” Schick said. “It
is based on the strength of the user’s muscle system. If they want the
elbow to move quickly, they will make a strong contraction. The goal is for the
user to have the confidence to pickup all sorts of objects and feel as if they
are not going to crush or drop them.”

If the user wishes to pick up an egg, they can finely control grip based
on muscle contractions.

In order to receive the new elbow prosthesis, the patient is required to
undergo the TMR surgery.

“This elbow in particular allows input from the different electrode
sites that were created during surgery,” Schick said. “Someone who
has not had the surgery would wear the standard arm.”

According to Schick, only a small number of individuals have used the
Dynamic Arm TMR. However, those who have donned the prosthesis have given the
prosthesis rave reviews and there have been no complications due to the TMR

Schick had the opportunity to visit one of the first patients to undergo
TMR surgery and wear the new elbow device. The patient had lost both of his
arms as a result of a high voltage accident and was initially fit with a
standard myoelectric arm. However, he was completely dependent on other people
in order for him to perform daily living activities.

“After the surgery and after being fit with the new elbow
prosthesis, he regained his independence,” Schick explained. “He
learned to drive on his own and he even returned to work. The surgery made a
huge difference in what he was able to do with his life.”

Schick is concerned with how the industry’s advancing technology
can help the patient’s independence.

“We can talk about the technology as far as the cool things that
are in it, but when we are developing the product we really are looking at what
advantages are there going to be for our user,” Schick explained.
“What is will the device provide in order for the user to improve their
quality of life.” — by Anthony Calabro

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