Second chance: science gives a hand.
For Nichole Good, the afternoon of September 19, 1989, is unforgettable. It drizzled as her mom drove her to a babysitting job after school. They glided down slippery lanes in suburban Elizabethtown, Pennsylvania. All at once, says Nichole (who was then 13), "we watched in horror. A speeding car headed toward us on the wrong side of the road."
Nichole's mother veered to avoid collision--and smashed into a tree--on her daughter's side. The other driver sped off, never to be seen again. Nichole's mom escaped unharmed. But Nichole's seatbelt flew open and she was pounded against the car roof, flung like a rag doll from front seat to back.
When paramedics rushed her to the Hershey Medical Center, doctors confirmed Nichole had suffered a spinal cord injury and would be paralyzed for life. She would never again feel or move any part of her body from her chest down. For a girl who lived to ride her bike and planned to compete on her school swim team, the news was devastating.
Spinal cord injuries made headline news in May 1995, when actor Christopher Reeve was thrown off his horse, paralyzing him from the neck down. After her accident Nichole could still move her neck, shoulders, and upper arms. But she couldn't dress or feed herself. When she returned to school, a hired aide had to take notes for her--Nichole couldn't hold a pen.
But science has offered Nichole a second chance. At 17 she volunteered to receive a device called the NeuroControl Freehand System at the Shriners Hospitals for Children in Philadelphia. The Freehand System is one of numerous artificial devices now available for the disabled. Others include ear, heart, and elbow-joint implants. Nichole's hand implant lets her use her right hand once again to pick up a fork or pen.
Nichole is only one of 120,000 quadriplegics in the U.S., people who have lost movement and sensation in their arms and legs, due to spinal cord injuries. Paralysis occurs when the spinal cord, the column of nerve tissue from the brain down through the backbone, is damaged.
"The spinal cord is like a phone line connecting the brain to your muscles," says Douglas Anderson, professor of neuroscience at the University of Florida College of Medicine at Gainesville and scientist at the Veterans Affairs Medical Center. When the "phone line" is faulty or cut, your muscles don't get the message to move.
A LOT OF NERVES
The simplest move like picking up a can of soda involves a complex interaction of nerves and up to 58 muscles! (Just one index finger contains five muscles.) When you decide to pick up the can, your brain sends a command in the form of electrical impulses down your spinal cord. The spinal cord passes the message on to the peripheral nerves, nerves fanning out to your arms and legs.
Electrical impulses from the nerves stimulate your arm and hand muscles to contract. That contraction allows your hand to move toward the soda can and permits your fingers to grasp it. Your decision to pick up an object occurs in an instant--easy to take for granted unless, like Nichole, your command no longer works.
Nichole's accident badly bruised her spinal cord. An injury like a gunshot wound can sever the spinal cord. But in 85 percent of all spinal cord injuries the spinal cord gets bruised. "When you run into a table edge and bruise your leg, the skin turns purple," Anderson explains. "The same thing happens to your spinal cord." When you bruise your leg, injured muscle tissue heals itself. But in the damaged spinal cord nerve cells don't regenerate. They simply die and leave a cavity inside the cord.
In Nichole's case, the bruise damaged her spinal cord between the fifth and sixth cervical vertebrae ("cervical" refers to the neck). That means the nerve cells from Nichole's brain reach the end of the line at the fifth vertebra down her spinal cord (see spinal cord illustration).
People with a spinal cord injury at the "C5/C6" level can't use their hand and forearm muscles, explains Tony Ignagni, a biomedical engineer at NeuroControl Corp. in Cleveland, Ohio. "But they still have the ability to position their hands in space [by using their shoulders and upper arms]," he says. "They can place their hand around a cup, but they can't grasp it."
A SECOND HAND
This is where the Freehand System comes in. The device takes over the nerves' job and stimulates paralyzed hand muscles to contract. Doctors implanted a small stimulator in Nichole's chest. The stimulator sends signals to eight electrodes (conductors of electricity) that doctors sewed to Nichole's thumb and finger extensors and flexors--muscles that open and close the hand.
To further strengthen Nichole's hand, surgeons later performed a procedure called tendon transfer. They took a working muscle from her upper arm and attached it to the tendon--the tissue connecting muscles to bones--of a paralyzed muscle. The working muscle supplements the nonworking one.
A position sensor taped to her left shoulder allows Nichole to control her right hand muscles. The sensor acts like a joystick. When she wants to pick up a fork, for example, Nichole pushes her shoulder back to open her hand. Moving her shoulder forward closes her hand around the fork. To lock her hand in the closed position, Nichole flicks her shoulder.
Data from the sensor flows through a wire into an external control box located in Nichole's wheelchair. The box--a computer and batteries--is the powerhouse for the Freehand System. The computer encodes the information into radio frequency signals, and forwards it to a transmitting coil, which Nichole tapes on her chest over the implant. The coil then "tells" the implant which muscles to stimulate and when.
The Freehand System restores some movement in quadriplegics like Nichole. But it does have its limits. When she first heard about Freehand, Nichole had great expectations. "I thought I was going to be like the way I used to be," she says. "It's easy to forget you're using only eight muscles, compared to a normal person who might use 58." Those eight working muscles provide Nichole with two kinds of grasp. One lets her cup her hand to hold large objects, like a tennis ball. The other grasp allows her to move her thumb against her forefinger in a pinching motion, to pick up smaller objects like a pencil.
Today Nichole can brush her own teeth and feed herself again. In school she can write her own notes. That comes in handy now that she's a psychology major at Florida Southern College. After graduation Nichole plans to head to law school. For someone who figured she could never do anything on her own again, Nichole has truly been given a second chance.
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The backbone, which consists of several short bones called vertebrae, protects the spinal cord.
Vertebrae are divided into four sections: cervical (in the neck), thoracic (behind the ribcage), lumbar (at the lower back), and sacral (at the base of the spine). Scientists have assigned numbers to each vertebra, from the top of the spine to the bottom. For example, the cervical vertebrae range from C1 to C8.
Doctors classify a spinal cord injury according to its location in the spine. Nichole Good, for example, has a C5/C6 level injury--she can still move her shoulder and upper arms. When actor Christopher Reeve fell off a horse in 1995, he received a C1/C2 level injury, which left him paralyzed from the neck down. More parts of the body become paralyzed when damage is higher on the spinal cord.
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|Title Annotation:||hand implants for people with paralysis|
|Author:||Chang, Maria L.|
|Date:||Nov 17, 1997|
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