A bionic nerve’s power
It sounds like one of those fitness products peddled in late-night infomercials -- an implantable stimulator that electrically exercises muscles. But if current tests prove it effective, this miniature device could revolutionize the treatment of strokes and spinal cord injuries.
In these conditions, nerve signals that spark normal muscle function are blocked, causing paralysis. Over time, unused muscles atrophy, which can make rehabilitation and recovery more difficult. The new device, called a BION because it works like a bionic neuron, strengthens and retrains these muscles by mimicking the nerve impulses from the brain.
Scientists know that electricity can be used to activate nerves and muscles throughout the body, said Dr. Gerald E. Loeb, a biomedical engineer who invented the muscle stimulator at USC’s Alfred E. Mann Institute for Biomedical Engineering. “But the trick was to create something that worked inside the muscle without leaving wires dangling through the skin.”
Encapsulated in glass with electrodes at each end, the tiny device (it’s the size of two grains of rice) is injected with a large needle directly into the “motor spot” -- the place where nerve endings meet muscle. When the muscles are ready to be exercised, a magnetic transmitter coil is placed over that part of the body. The coil sends power and command signals to the implant, prompting it to emit electrical pulses that activate the muscles.
“This is a real advance over what we have to treat people with severe muscle weakness,” said Dr. Stephen D. Bagg, a stroke specialist at Queen’s University in Canada who has studied the device. Because it could be used at home, it is expected to be more convenient and produce better patient compliance. Although the technology won’t make anyone buff, it can reverse muscle atrophy, strengthen joints and enhance flexibility.
Therapeutic muscle stimulation is already used as part of physical therapy in patients who have sustained nerve damage. But current methods have drawbacks that limit their widespread use.
The more common treatment is an electrical stimulator used on the surface of the skin. However, the electrical jolts can be painful, too high a charge can burn the skin, and the impulses may not hit the muscle in the right place. On the other hand, devices inserted directly into the muscles have to be surgically implanted, with electrical leads protruding through the skin, which increases risks of infection and breakage.
The new device seems to be just as effective, but without these disadvantages. The first human tests of the bionic nerve began in 1999 in Canada, when the device was inserted into the shoulder muscles of 11 people who had recently suffered a stroke. The shoulder is a shallow joint and is held together by the activity of the muscles. When the muscles are flaccid, the weight of the muscles and the bone pulls the arm out of its socket, a painful shoulder dislocation that afflicts many stroke victims.
The study volunteers used the device, which can send up to 3,000 commands per second, at home for 20 to 30 minutes two to three times a day. At the end of six weeks, X-rays revealed that the therapy had strengthened muscles and that the shoulder joint either remained aligned or, if it had already slipped out of place, had returned to its normal position.
Italian researchers have also tested the bionic nerve on patients with osteoarthritis in their knees. Because sufferers avoid bending their knees because of the arthritis pain, the muscles often atrophy. In that 12-week study, the volunteers experienced a significant reduction in pain and disability, and one even postponed a scheduled joint replacement surgery, Loeb said.
Three new studies funded by the National Institutes of Health are currently enrolling a small number of stroke patients at USC and Rancho Los Amigos National Rehabilitation Hospital. One will use the BION to treat chronic shoulder pain; another will test whether the device can help restore muscle function in the hands; and the third will determine whether it can prevent muscle contractions in the hands, a condition known as claw hand deformity.
Although the technology is still in a relatively early stage, the bionic nerve eventually may be used to treat all kinds of disabilities that result from muscle paralysis, even serious spinal cord injuries, said Dr. Sophia Chun, medical director of outpatient clinical and rehabilitation services at Ranchos Los Amigos National Rehabilitation Center in Downey. “There’s a number of exciting potential applications,” she says.
Stroke symptoms and current therapies
Each year, more than 750,000 Americans suffer strokes, which are injuries to the brain caused by the blockage or rupture of blood vessels ferrying vital nutrients and oxygen.
Strokes cause different symptoms depending on where the damage occurred. When the brain region regulating specific movements is injured, it stops sending nerve signals to animate different muscles. As a result, many stroke victims suffer from speech and language difficulties, paralysis, persistent problems with balance and walking, or they may develop a condition known as spasticity, in which movement is difficult or uncontrollable.
Traditional stroke treatments include surgery to treat or repair brain damage, speech therapy and occupational therapy to relearn daily routine activities. Botox injections also are used to relax muscles stiffened by spasticity.
But physical therapy is the cornerstone of stroke rehabilitation. Research has shown that the brain has great capacity to recover and relearn, but the muscles must be strengthened and retrained. Without therapy, muscles can deteriorate and result in a permanent loss of function.
