CHICAGO — The first artificial disk approved for use in the United States offers patients with chronic degenerative disk disease an alternative to spinal fusion surgery, but beware: Surgeons have a steep learning curve for placing the device correctly.
The primary advantage of the Charite Artificial Disc system by DePuy Spine Inc., a subsidiary of Johnson & Johnson, is that it offers pain relief, motion retention, and earlier return to normal function, Charite clinical trial investigator Scott Blumenthal, M.D., said in an interview.
The Charite disk, which was approved by the Food and Drug Administration in October, is indicated for patients with single-level degenerative disk disease. The device consists of two cobalt chromium end plates and a polyethylene core. There's no secondary bone graft harvesting or fixation of the spine with screws and rods to stabilize, as in spinal fusion surgery. When implanted, the device restores the natural distance between two vertebrae and allows movement at the level of implantation. And unlike the strict limitation imposed on patients who have undergone fusion surgery, when the disk is implanted successfully, there are no movement restrictions, said Dr. Blumenthal of the Texas Back Institute, Plano.
The European experience with the Charite, which dates back 2 decades, suggests it also may reduce adjacent degenerative disease better than fusion surgery, although this hasn't been specifically evaluated in clinical trials.
The FDA is requiring DePuy to conduct a long-term effectiveness and safety study of patients who have the device implanted, which will include assessing its impact on adjacent vertebrae, and on other bony structures in the back of the spine.
The artificial disk is currently being used at a handful of spine centers in the United States, and as more surgeons become trained in the procedure, it should become more widely available. Surgeon training is mandatory, and the learning curve is steep.
“This procedure is intended for experienced surgeons who already are familiar with the anterior approach to the spine,” William Christianson, DePuy vice president of clinical and regulatory affairs, said in an interview. “These are for fellowship-trained surgeons who have a practice focused exclusively on the spine. We don't want knee arthroplasty guys coming to our course. They won't be able to get in.”
There are about 2,000–2,500 surgeons in the United States who have the training and the experience to qualify for the course, he estimated.
A new study, evaluating the learning curve associated with Charite implantation in patients with symptomatic degenerative disk disease at L4-L5 or L5-S1, has shown that surgeons at high-volume investigational trial sites had shorter operative times (85 minutes versus 127 minutes), compared with surgeons at low-volume sites, John Regan, M.D., reported at the annual meeting of the North American Spine Society.
Patients at the high-volume sites also left the hospital 1 day earlier than patients in the low-volume group (3.5 days vs. 4.5 days). Major complications of neurologic deterioration (14.1% vs. 4.5%, respectively) and device failure (4 cases vs. 1 case, respectively) occurred significantly more often in the 85-patient low-volume group, compared with the 120-patient high-volume group.
Absolute change in visual analog scale (VAS) and Oswestry Disability Index scores was similar in both groups.
“Implant positioning is very important, and in our particular series at Cedars [Sinai Medical Center in Los Angeles] we noticed we improved from the first 10 to the last 10 cases,” said Dr. Regan, who is a consultant for DePuy.
Surgeons new to the procedure should limit themselves to single-level replacement. However, two-level replacements have been implanted outside the United States, demonstrating that the technique is “very viable,” said Dr. Blumenthal, who is also a consultant for DePuy and receives funds to lecture on the device.
Approval of the device was based on a 15-center study involving 304 patients who underwent back surgery for symptomatic disk degeneration that was unresponsive to 6 months of nonoperative treatment. Of the total, 205 were randomly assigned to receive a single-level Charite disk, and 99 received anterior lumbar interbody fusion using Bagby and Kuslich cages.
At 2 years of follow-up, those patients who had the artificial disk “did no worse” than those who had intervertebral body fusion with similar rates of adverse events in both groups, according to an FDA statement issued at the time of approval. There was no significant “relationship between motion at the level where the disk was implanted and the patient's relief from pain.”
Mean operative time and estimated blood loss were similar in the two groups. Hospital stays were significantly shorter among Charite patients, compared with fusion patients (3.7 days vs. 4.3 days), Dr. Blumenthal reported at the meeting.