Medical Device Daily Washington Editor

WASHINGTON — The 2007 meeting of the American Association of Neurological Surgeons (AANS; Rolling Meadows, Illinois) delved into some of the developmental difficulties and controversies over artificial spinal disc technology, which has kept reviewers at FDA busy in the past few years.

Paul McCormick, MD, a professor of neurosurgery at Columbia University College of Physicians and Surgeons (New York) discussed the relative merits of lumbar fusion vs. disk replacement in a lecture titled "Lumbar Disk Replacement: Success or Failure."

"Whenever you evaluate new technology, there are a number of questions you have to ask: is it feasible, safe, effective? Does it provide equivalent or additional benefits?"

McCormick reviewed some of the data for the Charité trial and then discussed events at the Centers for Medicare & Medicaid Services in connection with the Charité , made by DePuy Spine (Raynham, Massachusetts), a business of Johnson & Johnson (New Brunswick, New Jersey).

Up to February 2006, CMS had issued no coverage decision on the Charité , leaving the decision up to local carriers. However, Richard Deyo, MD, the co-director of the University of Washington Center for Cost and Outcomes Research (Seattle) had appealed to CMS the previous August to issue a decision of non-coverage, forbidding any Medicare contractors from paying for the Charité .

In the Feb. 15, 2006, decision memo, a team of administrators at CMS, who admitted that they did not consult with the Medicare Coverage Advisory Committee on the matter, indicated that they saw "insufficient evidence for those over age 65 to determine net health benefit, with the suggestion that the Charite disc is not indicated in this population for a variety of reasons." One of these was that the outcome of the PMA non-inferiority trial was "unconvincing as a demonstration of net health benefit."

Apparently referring to the CMS reference to "net health benefit," McCormick remarked: "Talk about a Catch-22, it was a non-inferiority trial and they were using it to try to establish whether there was superiority." He noted that CMS took in 604 comments on that decision, only 7 of which agreed with the non-coverage outcome.

However, McCormick pointed out that 470 of the dissenting comments were sent in form letters printed by the Texas Back Institute (Plano, Texas).

Nonetheless, CMS reversed field in part, indicating that the "Charité lumbar artificial disc is not reasonable and necessary for the Medicare population over 60 years of age," but opted to leave the door open for beneficiaries aged 60 and younger by making no national coverage determination, "leaving such determinations to be made on a local basis."

Still, McCormick said that he doubted whether the Charité would be widely adopted due to "the narrow indications, the marginal comparative benefit, technical considerations, and unproven long-term benefits," and described lumbar disc replacement as "a critically acclaimed success, but ultimately, a box office failure."

All the same, McCormick suggested that the firms in the cervical market should take heed of DePuy's experience. While he made the case that about "50% of our patients" are good candidates for cervical disc replacement, "I think the current investigators really went to school from the Charité " experience with CMS.

Much of the data for cervical discs is meaningful, McCormick noted, but "here's the problem: it's likely – in fact, I think it's guaranteed — any new technology will have to run this gauntlet" that seeks to establish a net health benefit over the existing standard of care.

"What I will tell you is that they will adopt an almost prosecutorial attitude in trying to prove the null hypothesis," giving alternative interpretations of data and presenting data that was not included with the sponsor's presentation. "They will come up with a number of concerns," including the cheerleader/placebo effect, and "will question some of the biological plausibility results" such as back pain and return to work.

CMS will raise a flap about some statistical elements as well, McCormick said, including "the fact that there was no reporting or analysis of Prestige radiographic failures" and the use of a one-sided test for statistical significance.

"What they'll do is review the slides . . . and say that 'gee, these are very similar, if not identical scores with regard to neck pain and arm pain,'" among other things. McCormick said that the placebo effect will be questioned because of a negative attitude toward fusion. "Is this a concern?"

Prior to McCormick's presentation, Regis Haid, Jr., MD, a founding partner of Atlanta Brain and Spine Care (Atlanta), discussed several of the current crop of artificial disc devices heading toward commercialization as well as some of their inherent limitations.

Haid immediately made the case that "artificial cervical arthroplasty (insertion of an artificial disc) will not supplant cervical arthrodesis," or fusion, which will "continue to be the workhorse" of spinal surgery.

"Cervical arthroplasty is relatively new since 1991, so as we gain experience, clarification will occur" on the question of patient selection. At present, the only good data is "on single-level disease," Haid remarked.

"Normal motion is what we're trying to replicate," but the types of motion "varies among levels of the spine" and according to Haid, the cervical spine moves "differently at every level."

So, while "all arthroplasty devices should replicate" all directions of motion, none of them will improve on the patient's inherent range of spinal motion. And one thing that no devices currently coming to market address is kyphosis, or spinal curvature.

Haid said that wear, imaging and toxicity are the three major issues for arthroplasty, and the combinations of materials exhibit different behaviors. Some have speculated that metal-on-metal devices, such as cobalt chrome discs, may create ionization locally and even migrate to the bloodstream, but he said that "so far, this has not been borne out." Metal-on-polyurethane combinations have sparked fears of resorption into the bone via the process of osteolysis, a possibility that must be dealt with because "the last thing we want to do is to put an artificial disc deeper into the spine."

As for post-operative imaging, surgeons who want to keep a close eye on how the artificial disc is located have a dilemma. Haid said that for metal-on-metal units, cobalt chrome "is the worst [for imaging] and titanium alloys image the best. However, cobalt chrome wears the best" and titanium exhibits inferior wear properties. "The problem is that MRIs are not optimal" for this kind of scan because this technology is more adroit at soft-tissue imaging.