Artificial disc replacement investigated by physicians
by Jim Dryden
April 18, 2003
University physicians are testing an investigational treatment for cervical disc disease that involves replacing a diseased spinal disc in the neck with an artificial one.
"The idea of replacing the disc is not new," said K. Daniel Riew, M.D., associate professor of orthopaedic surgery and chief of the cervical spine service in the School of Medicine. "But in the past, the technology was not available to have a disc replacement that could last for a long time and provide the range of motion that mimics what one has in the natural spine."
Riew and colleagues Brett A. Taylor, M.D., assistant professor of orthopaedic surgery, and Neill M. Wright, M.D., assistant professor of neurological surgery, will compare the success of artificial disc replacement to the current "gold standard" procedure for cervical disc disease: anterior cervical discectomy and fusion.
During discectomy, a surgeon removes the ruptured disc and then fuses together the vertebrae that had been separated by that disc.
"We know that the anterior discectomy and fusion works very well," Riew said. "Results are good to excellent for 90 percent to 95 percent of patients, but the hope is that the artificial disc will equal these results while maintaining the normal range of motion following surgery and prevent breakdown and deterioration in other parts of the cervical spine."
Cervical disc disease is a common problem in the United States, and almost everyone will develop it at some point.
The disc is often compared to a jelly donut because it has a squishy center surrounded by a tough outer portion. It functions like a shock absorber between the bones of the cervical spine.
When a disc ruptures, or becomes herniated, the squishy disc tissue can move into the spinal canal and press against nerves, causing numbness, weakness or pain in the neck and arms.
Only a small percentage of patients with spine problems ever require surgery, but that still amounts to more than 250,000 spinal fusion operations in the United States every year.
There are eight motion segments in the neck. When a disc is removed and the vertebrae are fused, a patient has one less level of motion. But the cervical spine still must bear the same load and undergo the same amount of stress from movement.
Riew said that fusing two levels together puts a bit more stress on the remaining vertebrae in the cervical spine and causes breakdown to occur slightly faster. The hope is that the artificial disc will slow that breakdown.
But whether it will work is not known. Only about 40 patients in the United States have had artificial cervical disc replacement surgery.
In Europe, about 1,000 patients have undergone the procedure. In the two to three years since the first European patients had their discs replaced, the results appear promising, but Riew said many more patients must have the procedure and much more time must pass before investigators can say whether artificial cervical discs provide a good alternative to traditional fusion surgery.
"We may learn that patients don't do well four or five years after the procedure and end up abandoning artificial cervical discs," Riew said. "The nature of investigational surgery is that we don't know for sure what will happen."
The University site is one of 21 in the United States currently recruiting patients for this study, but only a handful of patients have enrolled. Riew has performed three artificial cervical disc replacement procedures the first ever done in either Missouri or Illinois.
To be eligible for the study, patients cannot have had any previous cervical spine operations. They are not eligible if there is disc disease at more than one level in the cervical spine or if they have a great deal of arthritis in the neck.
"That excludes the vast majority of patients," Riew said. "I do several hundred cervical spine operations in the course of a year, but of those several hundred patients, only about 20 or 25 patients (less than 10 percent) actually qualify for this study."
Those patients who qualify are randomly chosen to receive either artificial disc replacement or the standard discectomy and fusion surgery. A computer will decide which procedure a patient receives. Both groups of patients will be followed for at least two years to compare the two procedures.
Riew emphasized that this is an investigational procedure and that patients who are randomized to receive the disc replacement will be taking a risk.
"Although the patients that randomize to the fusion procedure tend to be disappointed, we must remember that fusion still remains the 'gold standard' operation for cervical disc disease," he said.
Riew said patients who think they may be candidates should discuss the idea of artificial disc replacement with their physician.
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