Super Natural
Implantable devices that replace defective body parts not only take over
where nature left off, they often improve on the original design.
by Monika Guttman
Even in its heyday, the 1970s TV show “The Six Million Dollar Man” was considered more comic book than high-concept science fiction. The premise—an astronaut/test pilot who crashed, mangled his body and was pulled back from the brink of death with whiz-bang bionic technology—seemed absurdly far fetched at a time when veterans just back from Vietnam were still being issued World War II-era prostheses.
Yet who could resist such a cool notion—body parts that were better than the original? So Col. Steve Austin, a.k.a. the Six Million Dollar Man, became the first primetime cyborg superhero, complete with a bionic eye that let him see extraordinary distances, bionic legs that let him run faster than a speeding locomotive and an arm that could lift and throw trucks.
Thirty years later, implantable “bionic” technology—while not yet offering patients the ability to throw trucks or outrun trains—is pulling many people back from the brink of death, debilitation and despair. Thanks to new materials that are not rejected by the body, decades of microminiaturization, electronic refinements and enormous advances in surgical techniques, implantable devices now help patients hear if they are deaf, see if they are blind and move if they have injuries. And that is just the beginning. On the horizon are minuscule machines that will take over the functions of damaged organs, rebuild teeth from the inside out or grind through the life-threatening plaque that clogs arteries.
Here is a brief look at some of the unbelievable implantables already available at the Keck School of Medicine of USC in what many are calling the decade of the device.
Airway
Intraairway stents: A number of conditions, such as lung cancer or complications from intubation or lung transplant surgery, can create a narrowing or obstruction of the air passages of the lung. In the past, opening the air passages and putting in a stent—a tiny tube that would hold the airway open—required a surgical procedure under general anesthesia. Now pulmonologists such as Richard Barbers, M.D., professor of medicine at the Keck School, perform an outpatient procedure in which the new intraairway stents are inserted through the mouth and down the air tubes under only light sedation. The reason: the new stents are made of metal, wire, nylon or other plastics and are much more flexible than the old stents. “It results in a completely different quality of life for these patients, who otherwise would not be able to breathe easily or would suffer infections,” says Barbers. He has used intraairway stents to prevent cancer from growing back after removing cancer growth with a laser. He also has used stents to bolster a weakness in the airway wall.
Bladder
Sacral nerve stimulation: Approved by the U.S. Food and Drug Administration in 1997 for urinary problems, sacral nerve stimulation is an effective treatment alternative for those who suffer from urinary retention problems and symptoms of an overactive bladder, such as leaking that may occur when there is a strong urge to urinate. And it might work on the bowel as well. “Bowel and bladder problems, as well as genital prolapse, are reaching epidemic proportions,” says Howard Kaufman, M.D., chief of the division of colorectal surgery at the Keck School and director of colorectal surgery at USC University Hospital. “Obesity, aging and injuries due to vaginal childbirth contribute to pelvic floor dysfunction. Due to these factors, a woman’s lifetime risk of requiring reconstructive surgery for pelvic organ prolapse or incontinence is 11 percent.” For urinary incontinence, if more conservative therapy fails—including medications, biofeedback training and some surgical procedures—a neurostimulator about the size of a stopwatch can be implanted near the sacral nerve in the lower spine. It sends small, electrical impulses to the sacral nerve, which controls voiding function. The continuous electrical stimulation reduces or eliminates urge incontinence. “There are many neural pathways affected by sacral nerve stimulation. The exact mechanisms by which sacral nerve stimulation improves bladder and bowel functions are the subject of active research,” Kaufman says. “Candidates for the sacral nerve stimulator undergo a less invasive ‘test drive’ procedure before getting the device. If symptoms are improved, the full implant is delivered in a second minor procedure.” David Ginsburg, M.D., assistant professor of urology, implants this device in patients with urinary incontinence. Kaufman is the principal investigator for sacral nerve stimulation trials now underway at USC for patients with bowel-continence problems.
Bowel
Artificial bowel sphincter: Anyone who has had irreversible damage to the anal muscle—through surgery or injury or treatment for disease—knows how few options there have been to correct the problem. Until now. A recently approved artificial bowel sphincter can operate just like the sphincter itself, allowing the patient to go to the bathroom normally. “It looks like a blood-pressure cuff,” says Kaufman. “It has a self-contained reservoir filled with fluid that goes around the anus, with a switch that goes into the scrotum of a man or labia of a woman.” Pressing the switch allows the fluid to flow from the cuff, which permits the patient to go to the bathroom. Then the reservoir refills, essentially cutting off the flow of fluids and solids until the next time. This device was first approved for urinary incontinence and was mainly utilized for men with urinary incontinence after a prostatectomy.
Ear
Cochlear implants: Cochlear implants have been around since the 1960s, but
new devices with bi-directional telemetry provide patients with more than
four times the amount of auditory 
information
available in previous cochlear implants. Unlike hearing aids, which are external
devices that merely make sounds louder, the implant is an electronic device
that is surgically implanted in the ear itself. The device bypasses damaged
parts of the ear by sending electrical “sound” signals directly
to the hearing nerve. “It doesn’t change the underlying problem
that makes a person deaf, but it circumvents that problem,” says Dennis
Maceri, M.D., associate professor of otolaryngology and a head and neck surgeon
at the Keck School. The newest versions come closest to replicating real hearing
because of improvements in the computer technology inside a chip in the implant.
“Because it stimulates all locations of the cochlea simultaneously, it
more closely approximates the normally functioning ear,” he says. The
implant can even work for someone with a hearing impairment since birth, as
long as there is a functioning auditory nerve. The device consists of surgically
implanted and externally worn components. The external components include
a speech processor (usually worn on the belt like a pager), a headpiece (worn
just behind the ear) and a thin cable that connects the two units. Patients
with the implant can swim, shower and do virtually everything normally, says
Maceri. “This is something that is not in the future—it is now,”
he says.
Eye
Intraocular retinal prosthesis: A number of diseases can damage the retina—the nerve tissue of the eye that receives images and transmits visual impulses to the brain. These include retinitis pigmentosa and macular degeneration. The result: patients lose their sight. Now Mark Humayun, M.D., Ph.D., and Eugene de Juan Jr., M.D., both Keck School of Medicine professors of ophthalmology at USC’s Doheny Retina Institute, are having great success helping the blind recover sight in clinical trials with a microelectronic retinal prosthesis that is intended to stand in for the damaged retinal cells. The implant is a sliver of silicone and platinum that is often referred to as an “eye chip.” It measures 4-by-5 millimeters, is attached to and sits atop the retina and is studded with 16 electrodes in a 4-by-4 grid. The device is being produced by Valencia, Calif.-based Second Sight, LLC. It works by electrically stimulating the remaining healthy retinal cells via the electrodes; the retinal cells, in turn, pass on the visual information to the brain via the optic nerve. So far, testing in some of the patients with the microelectronic implant revealed that they were capable of detecting when a light is turned on or off, describing the motion of an object, and even counting discrete objects. Tests now underway “look at how useful the prosthesis can be in activities of daily living,” says Humayun.
Heart
Drug-eluting stents: Until recently, badly blocked heart arteries were generally treated with bypass surgery—a complicated procedure in which plaque-clogged arteries were “bypassed” with veins that connected the aorta to the blocked artery. Procedures such as angioplasty—where a tiny balloon is inflated inside the artery, increasing its diameter—were not as effective as a bypass because scar tissue would form, making the blockage as bad as or worse than before. In the early 1990s, physicians began to employ “stents”—tiny mesh tubing put inside an artery to hold it open after angioplasty. Although the stents worked better than angioplasty alone, some 20 percent of patients still experienced “restenosis”—the growth of scar tissue that blocks the arteries again.
Recently, doctors such as Alex Durairaj, M.D., assistant professor of medicine at the Keck School, have begun using new stents coated with a medication that reduces the build-up of scar tissue. These drug-eluting stents, says Durairaj, are covered with Rapamycin, a drug that has been used to prevent kidney rejection. So far, these drug-coated stents have curbed restenosis because the Rapamycin leeches into the artery at the site of deployment and prevents the cells that lay down scar tissue from multiplying. “Restenosis has been the Achilles heel of interventional cardiology,” says Durairaj. “Patients who developed restenosis were often referred to bypass surgery. Now that restenosis has been ‘conquered,’ we should not need bypass surgery for these types of patients.”
Biventricular pacemakers: Standard pacemakers have been around for decades, helping patients with abnormally slow heart rates. These pacemakers are inserted in either the lower right chamber of the heart or both the lower right and upper right chambers. But the real pumping action of the heart comes from the left side—the left ventricle. For the past six years, physicians such as Leslie Saxon, M.D., Keck School professor of cardiovascular medicine and director of electrophysiology at the USC University Hospital, have been testing new biventricular pacemakers, which paces both the left and right lower chambers (ventricles) of the heart simultaneously, causing the heart to beat more efficiently in these patients. “It improves the way patients feel and is an incredible alternative for people who would otherwise either need a transplant or die,” Saxon says.
Implantable defibrillators: Some patients with heart failure are at high risk of sudden death from heart rhythms gone awry—a too-rapid rhythm in the ventricles that can restrict blood flow to the body and result in fainting or death. The rapid rhythm occurs when electrical impulses that tell the heart to contract are sent too quickly through the heart muscle. Defibrillators deliver energy to the heart to restore normal rhythm. In the past, defibrillation has come from large external devices, but for the past few years Saxon has been implanting a tiny defibrillator in the heart that senses dangerously rapid rhythms in the ventricles and immediately delivers energy to the heart to restore a normal rhythm. “It’s like having an emergency room implanted in your chest,” she says, noting that this is the device Vice President Dick Cheney had implanted for his heart disease.
Knee
Genetically engineered cartilage: Although joint replacement surgeries are now commonplace, the artificial joints wear out in 10 to 15 years and need replacement themselves. So orthopaedic surgeons have long dreamed of replacing damaged tissue with live tissue instead of a mechanical device. These days it can be done, says C. Thomas Vangsness Jr., M.D., professor of orthopaedics at the Keck School and associate director of the Center for Athletic Medicine at USC University Hospital. A new procedure called autologous chondrocyte implantation can replace the articular cartilage, the covering on the ends of the bone in the knee that is often damaged by sports, traumatic injuries or daily wear and tear. Patients younger than age 50 with localized small defects in the articular cartilage are the main recipients of this procedure. The diseased cartilage does not have a natural ability to heal and, if left untreated, the damage may spread to surrounding healthy cartilage and cause deterioration of the joint surface. In the procedure, available since 1995, Vangsness takes a small sample of the healthy cartilage tissue in the knee (about the size of two pencil erasers) with a simple arthroscopic procedure. Cells from the cartilage are grown for about five weeks, or until there are enough to repair the knee. When the cells are mature, they are surgically returned to the knee, where they heal and, with time, mature enough to form a cartilage repair. The difficult part during the six months or more when the cells are maturing is that patients must limit their activities and go through rehabilitation. But the end result, says Vangsness, is a knee “that generally functions with much less pain.”
Pancreas
Insulin pumps and glucose sensors: Insulin pump technology—a huge boon for diabetics who have to give themselves injections throughout the day—has been around for about 20 years. Thanks to technologic advancement, new models are easier to use and smaller, about the size of a pager. Diabetics get insulin into the body through a catheter in the skin that is replaced every three days.
Sensors to measure glucose levels continuously may someday do away with the need for six to 10 skin pricks a day to monitor blood glucose. Sensors such as the Minimed Continuous Glucose Monitoring System, which monitor blood glucose through the skin, “read and store the blood sugar levels over the past two to three days to help alert patients to high or low blood sugar conditions, rather than giving a reading in real-time,” says Anne Peters Harmel, M.D., director of USC’s Westside Clinical Diabetes Program. So the Holy Grail for diabetics and those who treat them are implantable versions of the pump and monitors or, ideally, a combination of the two. Insulin pumps can be implanted now, but “it requires major surgery and is limited to research use,” says Harmel. Implantable sensors are on the horizon, as are devices that combine both a sensing and insulin distribution system, making life much more manageable for those who need to regulate their blood glucose levels.
Spine
Artificial discs: The discs of the spine act as shock absorbers. They are made of hard bone with spongy material inside that take the brunt of the impact when someone walks, jumps or sits. Patients with degenerative disc disease endure excruciating back pain, numbness and tingling in their arms or legs, and a host of other symptoms that make life miserable. New artificial discs—man-made devices that replace the defective disc in the spine—may bring relief to those who have not responded to non-surgical remedies such as anti-inflammatory medications and injections. “The previous surgical remedy was spinal fusion,” notes Mark Spoonamore, M.D., Keck School assistant professor of clinical medicine and orthopaedics and director of the Center for Orthopaedic Spinal Surgery at USC University Hospital. “But that means solidifying everything, so there is generally no motion in the area of the spine that has been fused, usually the lumbar or lower spine.” That, in turn, puts greater stress on the rest of the spine—and often results in further surgery. There are a number of new artificial discs in trials; by replacing the defective disc, “the patient’s life is improved by allowing mobility of the disc, which ranges from 3 to 7 degrees per disc level,” he says. “That is a lot.” The artificial discs have been used for the past 14 years in Europe, but in trials here for only the past three years. Spoonamore expects one disc will be FDA approved within the year, and USC University Hospital is slated to be one of the first places to provide the surgery.
Teeth
Dental implants:
When the first modern dental implants became available in the 1950s, fewer
than half of all implants lasted longer than five years, largely because the
body viewed them as foreign and rejected them. In the search for an implant
that would not arouse the body’s defenses, dentists tried more than 50
materials, including stainless steel, ceramics and aluminum, with varying
degrees of success. Harold C. Slavkin, D.D.S., dean of the USC School of Dentistry
and the G. Donald and Marian James Montgomery Dean’s Chair in Dentistry,
says that in the last five years, specially molded and milled titanium-alloy
implants have advanced so much that greater than 95 percent of them are in
place five years later. More than 1 million dental implants each year are
done, and “the expectation for the clinician and the patient is that
an implant will last 40 years or more. That is longer than the average life
expectancy of a person at the beginning of the 20th century,” Slavkin
says. Titanium-alloy implants can be made to mimic bone at the micron level,
providing pits and grooves and gaps where blood vessels, cells and connective
tissue can grow. As a result, the body treats the implant as a compatible
body part and fuses with it. Further, the implants have medical uses that
greatly exceed the replacement of teeth, Slavkin says. The same technology
used to custom-shape dental implants is used to reconstruct major portions
of facial bones and eye sockets for people with birth defects or those who
have suffered severe trauma.
Tendons
Soft tissue patch: The expression may be “in a pig’s eye,” but it is implants from the pig’s intestines that are giving surgeons new hope. Keck School orthopaedists are implanting a patch made from pigs’ small intestines to improve healing of surgically repaired tendons. The patches, which for some reason appear to have reviving properties, are meant to scaffold or support tendons while they heal. Traditionally, surgeons have had to graft patients’ own tissue or donated tissue to replace lost tendons or reinforce damaged tendons or ligaments. The new patches allow for reinforcing tendons without invasive removal of other tendons or ligaments. The FDA approved the patch, commercially known as the Restore Orthobiologic Soft Tissue Implant, in October 1998. “I use the patch in surgery if the tissue looks friable, or appears to be at high risk of rupturing again,” explains John M. Itamura, M.D., assistant professor of orthopaedic surgery at the Keck School and associate director of the Center for Athletic Medicine at USC University Hospital. James E. Tibone, M.D., Keck School professor of orthopaedic surgery, is running a study in animal models to examine more extensive use of the patch for rotator-cuff problems. The patch holds promise in other applications as well, such as cardiovascular repair, urologic surgery and cancer recovery.
Metal. Mechanics. Man-made tissue. For much less than $6 million, people are walking taller and hearts are beating better with bionic devices that are not part of the future, but part of the life-saving technologies of today.
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