The Charite artificial disc was first approved for use in the US in October 2004, although it had been used in the European market since 1987. The device was approved to relieve pain by replacing the damaged disc with the Chirate disc, as an alternative to the surgical procedure known as lumbar spinal fusion surgery.
The disc was developed with the premise that segmental mobility will improve outcomes, as has been the case for artificial hip and knee replacements. The current Charite disc is the third modification of a device first developed in 1982 by Buttener-Janz and Schellnack at the Charite Clinic in the former East Germany.
At present, experts claim, the best candidates for disc replacement are adults who have disc degeneration in only one disc in the lumbar spine, either the disc between the fourth and fifth lumbar vertebrae or the disc between the fifth lumbar vertebra and the sacrum.
Under FDA guidelines, before disc surgery, individuals must have undergone at least 6 months of treatment, such as physical therapy, pain medication, or wearing a back brace, without showing improvement, and must be in overall good health with no signs of infection, osteoporosis or arthritis.
Experts stress the importance of making sure a patient is the right candidate for this surgery. According to Dr Stephen Hochschler and Dr Paul McAfee, examples of how inappropriate patient selection can have serious consequences are:
"If a patient receives an artificial disc, but the disc that was replaced was not actually the cause of the patient's pain, then the patient will have undergone an extensive, invasive and costly procedure but still have the same level of pain. This may seem like an incredibly obvious point, but with back pain it is often difficult to pinpoint the precise cause of a patient's pain. Accurate and careful diagnosis of the patient's pain generator is crucial and cannot be overemphasized.
"If the patient does have a painful disc, but other factors (such as significant degenerative changes in the facet joint) are present, then the patient may have to undergo a revision surgery after the initial surgery to either correct the placement of the disc or fuse the spine—a situation that is definitely best avoided by correctly assessing all the risk factors prior to the first surgery."
Many critics contend that the Chirate disc is just as big a threat to patients as the problems it is supposed to cure. The disc has been promoted as an alternative to fusion; yet, even in the short term studies, spontaneous and surgical fusion occurred.
The disc is required to function for many years, but information about long term benefits and risks, such as satisfaction, adjacent segment problems, and rate of re-operations, is not available because only one short term study, with a 24 month follow-up, was presented to the FDA when the disc was approved.
And even that study has come under attack because the benefits of the Charite in the context of a noninferiority trial, were shown to be noninferior to Bagby and Kuslich cages (BAK), used in spinal fusion, a failed procedure critics say that has not been performed in years.
The 2- year trial showed only that the disc was no worse than this specific type of spinal fusion surgery, according to a May 2005 FDA report.
Overall, the study found that 57% of Charite patients achieved "overall clinical success," compared with 47% of the spinal fusion patients. However, more than 3 out of 5 Charite patients, deemed successes, were still taking narcotic painkillers 24 months after surgery.
In addition, a higher number of Charite patients suffered severe or life-threatening events than spinal fusion patients, 15% compared to 9%, according to the FDA review.
Clinical success in the trial was defined by four criteria: (1) more than 25% improvement at 24 months after surgery, (2) no device failure, (3) no major complication, and (4) and no neurologic deterioration.
This composite outcome is unconvincing as a demonstration of net health benefit, according to a February 15, 2006, Memorandum, from the Centers for Medicare and Medicaid Services (CMS), particularly when these points are also considered:
"1) only 57% of disc replacement patients and 46% of BAK fusion patients met these four limited criteria; 2) in patients who were considered a clinical success at 24 months, 64% of the Charite group and 80.4% of the control were using narcotics; 3) at 24 months the change in VAS and ODI did not differ statistically from control; 4) the SF-36 PCS and MCS composite scores did not differ statistically from control; 5) no difference in operative time or blood loss between the two groups."
According to the CMS Memorandum, the surgical procedure for disc replacement involves an anterior approach for exposure of the spine. With this approach, complications of vessel injury can occur and have the potential to be life threatening (Santos, Polly et al. 2004). As to revision surgery, Santos, et al, state:
"Revision surgery for a failed disc arthroplasty is life threatening. Dealing with the scarring around the great vessels is the main challenge. Indeed, the location of vital vascular structures may make it altogether impossible to perform such anterior abdominal exposures."
Other postoperative difficulties such as infection, persistent pain, instability, and osteolysis can also occur (Santos, Polly et al. 2004).
In recent years, the cost benefit of surgery for degenerative disc disease has come under scrutiny. The 2005 Cochrane review of surgery for degenerative lumbar spondylosis states, "There is no good evidence on cost-effectiveness" (Gibson, Wassell 2005).
Concern over the cost benefit has been expressed specifically for the artificial disc. Within 5 years of its release, the CMS noted, it was predicted that spinal arthroplasty (lumbar and cervical) could reach an annual cost of $2.18 billion in the US, with the suggestion by Singh that this estimate is conservative (Singh, Vaccaro et al. 2004).
Santos stated, "...long-term clinical outcome using validated instruments are necessary to justify the added cost of these procedures."
Dr Sohail Mirza, a medical professor at the University of Washington, criticized Charite's marketing slogan of "natural motion is back." It "implies that the artificial disc creates a normal spine; it does not," he stated last year in the journal Spine.
"Contrary to optimistic marketing, the data," he wrote, "argue for caution by patients and surgeons. Hope for a cure of back pain and a marketing bonanza must be held in check."
As of July 2006, more than 130 serious adverse events have been reported to the FDA associated with the Chirate disc.
In 2005, the FDA performed an analysis of adverse events reported in the Manufacturer and User Facility Device Experience Database (MAUDE), at the request of CMS. The analysis includes Medical Device Reports (MDRs) that were entered into the database between August 11, 2003 (first report received) and November 16, 2005.
A total of 101 MDRs were analyzed for 96 patients, with 1 MDR for the Prodisc device in addition to the Charite devices.
The most frequently reported event was device migration out of the implanted location, with 54 of 96 patients (56%) experiencing this effect. Seventy-six patients (79%) had a second surgery to remove all or part of the implant, to correct problems with the device, or to correct problems produced during the surgery. Fifty of the 76 (66%) patients had second surgery due to device migration.
The most common second surgery was to remove all or part of the disc followed by spinal fusion of the implanted motion segment. Twelve patients had 2 prostheses placed despite the device labeling for only one device implantation. Most adverse events that required second surgery occurred in the first 2 months after implantation. Two deaths were reported which were both attributed to pulmonary emboli.
Dr Charles Rosen, associate clinical professor of spine surgery at the University of California, Irvine, told the LA Times on August 5, 2006, that he has seen 10 patients since late last year, complaining of worsening pain after receiving the Charite disc and that some patients suffered fracturing and an abnormal pulling apart of the joints of the spine.
He says the Chirate is unsafe and should never have been approved because a 2-year study is too short for a disc that will remain in the spine for many years with implant patients averaging 40-years old.
"There is no solid evidence that this will last for more than five or 10 years and they will not need to have another operation," Dr Rosen said.
According to Times, Dr Allyson Fried-Cain, 52, a former foot-and-ankle surgeon, has sued the device maker, saying she suffered such an increase in pain after a Charite disc implantation that she lost her practice and had to sell her home in Marina del Rey, California.
Dr Fried-Cain, a former marathon runner whose back injury resulted from a car accident, told the Times, "I couldn't do surgery anymore. I couldn't bend over,"
"This implant has destroyed my life," she said.
According to the Times, spinal surgery is becoming a very lucrative business, "with at least $3.2 billion spent last year in the U.S. on spinal fusion."
In August 2006, the FDA approved the ProDisc-L, made by Swiss medical device maker Synthes Inc, which is expected to compete against the Charite.
In its approval letter to Synthes, the FDA said patients receiving the disc should have tried at least 6 months of "conservative" treatment with other therapies such as exercise and medication.
As a condition of approval, Synthes agreed to continue studying the disc for long term safety and effectiveness in a study involving at least 286 patients. The company is also required to conduct a yearly analysis of major adverse events and report the number of devices sold and implanted each year.
The booming spine surgery industry suffered a serious financial set-back earlier this year, when the Medicare program stopped paying for the Charite disc in patients over 60, noting that the surgery costs between $30,000 and $50,000, and has not sufficiently been tested for long term affects. The CMS stated "that the evidence is not adequate to conclude that the Charite lumbar artificial disc is reasonable and necessary."
"Therefore," the CMS memo concluded, "we propose to issue a national noncoverage determination."