A Finer Grasp on the Electronic Hand

A Second Generation Neural Hand Prosthesis makes Life Easier for Patients 

From: Design News, Lifesavers: The Components behind Today's Medical
Breakthroughs - May 5, 2003 - page 17

By: Amy Castor

Six years ago, the Cleveland Functional Electrical Stimulation (FES) Center
brought hope to quadriplegics with its FDA-approved Freehand neural hand
prosthesis. By using electrical impulses to move paralyzed muscles on
command, the device restores some movement to the hand. In forging onward
with its work, the Center is now testing a second generation electronic hand,
with an implantable sensor, additional output channels, and a more naturally
means of operation. 

Similar to the original Freehand, the new implant targets people with nerve
damage at the 5th or 6th cervical root. Although these individuals can move
their shoulders and upper arms, their hands remain paralyzed. With the
ability to grasp objects, they gain the independence to do simple tasks like
brush their teeth or pour themselves a cup of coffee. 

Called "the second generation neural hand prosthesis," the new device retains
the basic components as the original. With Freehand, the user controls hand
movement through voluntary shrugs of his opposite shoulder. Moving the
shoulder forward and back, opens and closes the hand. An external joystick
position sensor near the shoulder reads the movements and sends the data to a
battery-powered controller on the wheelchair. The controller processes the
information into RF signals in order to send power and control an implanted
stelemeter/telemeter (IST) in the chest. (A coil taped to the chest transmits
the signals through the skin.) 

Caption 1a: In the original Freehand, the user controlled hand movements
through voluntary movements of the opposite shoulder. A position sensor taped
near the shoulder transduced the motion and sent the data to a
battery-powered control unit.  

Caption 1b: In the second generation neural hand prosthesis, the shoulder
position sensor is replaced by an implantable joint angle transducer in the
wrist. 

Eight subcutaneous wires carry the signals to electrodes sutured onto the
muscles of the forearm and hand to produce coordinated hand movements. 

Less to Dress 

Putting on the original Freehand was a chore. It consisted of taping the coil
antennae and the joystick position in place and running wires from both
objects under the shirt to a large black controller that hooked onto the
wheelchair. The process, which took about 10 mihutes, usually required some
assistance. 

"The whole idea for these neuroprostheses is to have essentially nothing
outside the body," says Dr. Hunter Peckham, director of the Cleveland FES
Center. "And that makes it considerably easy for patients because they dont
have things to put on and take off."  

Fewer external parts makes life easier for the patient. In the second
generation neural hand prosthesis, gone is the cumbersome shoulder-position
sensor. And in its place is an implantable joint angle transducer (IJAT) that
screws into the small bones of the wrist. The tiny device consists of a
titanium encapsulated array of three Hall effect sensors and support
circuitry implanted in the radius and an encapsulated rare earth magnet
implanted across the joint into the lunate. 

With the IJAT in place, users control hand movement more naturally with their
wrist instead of their shoulder. Dropping the wrist opens the hand, and
lifting it closes the hand. For patients who have CS injuries and cannot move
their wrists, the device also can be implanted in the shoulder. 

Another advantage is that because the IJAT receives its power through the
IST, the user has one less wire coming down from his chest to plug into the
external controller. 

Caption 2: Neuroprostheses like Freehand give quadriplegics, people paralyzed
from the neck down, the ability to use their hands for basic everyday things,
like answering a telephone.

As an alternative to using the voluntary muscles in the shoulder or wrist to
control hand movements, researchers at Cleveland FES are testing devices that
read the electric activity of muscles in the arm or neck. 

"One of the advantages to myoelectric activity is we can use it as a control
technique for people who have no wrist control, because their injuries are
higher up in their neck," says Peckham. "It would be more difficult to
implement but would be applicable to a larger number of people."  

More Mobility 

As surgeons got the hang of implanting Freehand in patients, they realized
that the eight output channels it offered for muscle stimulation were used up
pretty quickly. Although originally, the eighth channel was intended for
sensory feedback - a buzzing sound indicated how hard the hand was
contracting - it was more often gobbled up for additional motor function in
the wrist or fingers. A new IST in the second generation neural prosthesis
offers 12 channels. 

The four additional channels are used to give patients finer grasp, sensory
feedback, and as an added bonus, the ability to reach overhead. People with
C5 and C6 level injuries often can work their biceps but not their triceps,
so they cant extend their elbows. The ability to reach overhead opens up a
new world for some. 

"When you think about it, there's a lot of things above your head," says
Peckham. "When you're in a grocery store, for instance, you're not just
working at eye level or below."  

A new controller is more good news for patients using the second generation
neural hand prosthesis. No longer are they anchored to their wheelchairs by
Freehands hefty black box controller, which had to be lugged with them when
they moved elsewhere. The new controller resembles a pager, clips on to a
belt buckle, and uses AAA batteries. 

"The old controller was built as a research device to be programmable for
multiple devices," Peckham says. The new pager specifically tailored for use
with the neural hand prosthesis. 

Onward and Upward 

Researchers at the Cleveland FES Center have expanded the technology behind
the electronic hands to restore some movement in the legs of quadriplegics so
they can stand or transfer themselves out of the wheelchair, to control
bladder and bowel function, and to allow some patients to breath without a
respirator. 

Although these neural prostheses give those who are paralyzed a new found
freedom, in the scheme of things to come, the devices are still rudimentary. 

Now in the works at the Cleveland FES Center is an implantable system with a
rechargeable battery, a central processor, and a network cable backbone. From
a cable extending down the arm or leg, surgeons can attach various simulation
and sensor components to meet the individual needs of the patient. 

Perhaps, in as soon as 10 years, we'll see neuroprostheses that are smarter,
more modular, and fully implantable, with no batteries to change and no wires
dangling outside the body. 

Caption 3: The implantable joint angle transducer consists of a series of
three Hall effect sensors implanted in the radius and a rare earth magnet
screwed into the lunate.  
