Medical Device Daily Associate

In the wake of Tuesday’s report in the Wall Street Journal (WSJ) raising questions on the safety and durability of DePuy Spine’s (Raynham, Massachusetts) Charit artificial disc, Medical Device Daily thought it worthwhile to explore the clinical experience with the device further and to see what technology down the road might improve upon the Charit , the only device of its kind currently approved in the U.S. (MDD, Oct. 28, 2004).

The WSJ article questioned the effectiveness of the Charit , compared to the current gold standard of spinal fusion surgery in which the bones of the spine are fused together. The fusion procedure often relieves pain but may also restrict a patient’s range of motion and strain nearby discs, requiring further surgery.

In contrast, the Charit disc is designed to alleviate pain while helping to maintain mobility in the lower back, though the FDA noted in a talk paper, at the time of the device’s approval, that the disc does not always allow movement at the implant area or sometimes allows too much movement, which can place excess stress on the device.

Typically, two surgeons work together in the artificial disc operation. A general surgeon approaches the spine through an incision in the abdomen and carefully moves blood vessels and internal organs out of the way to provide access to the spine. A spine surgeon then uses special tools to remove the damaged disc to create a space between two vertebrae for the implantation of the artificial disc. The procedure generally takes 60 to 90 minutes and requires general anesthesia.

Overall, Richard Toselli, MD, vice president for research and development at DePuy, told MDD that he thought the WSJ piece, in which he was quoted, “presented balanced perspective on the issues and reflects the environment we are in with new technology.”

When any new technology is introduced to the market, he said, there is always a healthy dose of skepticism. “I think physicians are skeptical of new technology but are absolutely willing to try it. The company’s perspective is that we have to disprove that skepticism, if you will, with clinical data and clinical experience.”

Surgeons quoted by the WSJ said that they believe a wave of patients will suffer complications from the artificial devices over the next 10 to 15 years and will need to have them removed.

While DePuy said its tests have shown the Charit ’s plastic core able to withstand more than 80 years of wear and tear, it touted the devices’ ability to be replaced, if needed. And in a panel discussion on the impact of the artificial disc on spinal fusion this past November, Richard Guyer, MD, a spine surgeon at and co-founder of the Texas Back Institute (TBI; Plano, Texas) and a co-investigator in the Charit clinical study, cited this feature as a key to its increased usage. “The advantage of the Charit is that it can be replaced,” he said (MDD, Nov. 16, 2004).

But the WSJ article argued that artificial disc removal, in some cases, was not as easy as advertised. To remove a problematic disc, surgeons must go through a patient’s abdomen. Because scar tissue sets in after the initial surgery, it’s more difficult the second time to move the major veins and arteries that block access to the spine, increasing the risk of bleeding during removal.

Contrast this with spinal fusion failure in which doctors can generally access a problematic spot from the patient’s back, thus avoiding potential damage to vital organs.

Responding to this, Toselli noted that of 11 patients who needed repair surgery for the device in a key clinical trial, only two needed later removal. The others, he said, were able to get by with supplemental fusion surgery and didn’t need to have their abdomens opened a second time. He also noted that fixing a fusion surgery also occasionally requires a second abdominal cut.

Overall, according to Toselli, malfunctions with the disc are rare, with only about 5% of Charit patients needing a reoperation, in line with older surgeries including spinal fusion.

“With proper patient selection and good surgical technique [which the company says it has provided to more than 2,000 surgeons in specialized centers], the patients are generally very happy,” said Toselli. “We’re confident this is a definite improvement over fusion.”

History appears to back him up, with more than 10 years of data from use in Europe, where the Charit has been available since 1987 – and used to treat more than 6,500 patients without a major number of complications – originally as the flagship product of Link Spine Group (Bradford, Connecticut). DePuy, itself a Johnson & Johnson (J&J; New Brunswick, New Jersey) subsidiary, acquired Link in 2003 for $325 million, plus milestone payments.

While the European data, which is largely based on single series case reports from surgeons, is a useful tool, Toselli acknowledged that U.S. doctors specifically want good randomized, controlled trial data not yet adequately provided from the European arena. Toselli said that the European data, nonetheless, “is still truly long-term data, and if you look at a lot of spinal technology, there isn’t a lot of that kind of data out there when a product gets introduced to the States.” He added that this European data was particularly good for addressing the durability issues.

While last year, DePuy said that use of the Charit or any other artificial disc might replace 15% to 35% of fusion procedures, and says in its marketing literature that the disc is only an alternative to fusion, that could still translate into what the company said was a “very significant opportunity.”

By 2010, according to a recent estimate by JP Morgan, the market for artificial discs such as the Charit – with a list price of $11,500 – could approach $1.7 billion.

While J&J is the first company to garner a U.S. approval for these devices – and thus gain a share of the large opportunity – it’s obvious why other companies are clamoring to develop artificial discs for the lower back as well as the neck.

Others in this hunt include Medtronic Sofamor Danek (Memphis, Tennessee), with the Maverick Artificial Disc; Raymedica (Minneapolis, Minnesota), with its PDN-SOLO prosthetic disc nucleus; Replication Medical (New Brunswick, New Jersey), developing spinal nucleus implants; Spinal Dynamics (Mercer Island, Washington), with the Bryan Cervical Disc System and the Prestige Cervical Disc System; Synthes-Stratec (Oberdorf, Switzerland)-owned Spine Solutions (New York), with its ProDisc disc replacement device; Ranier Technology (Cambridge, UK) with its Cadisc spinal disc, a polyurethane disc prosthesis and Stryker (Kalamazoo, Michigan), via its 2004 merger with SpineCore (Summit, New Jersey), maker of the FlexiCore lumbar artificial disc, and the CerviCore cervical artificial disc.

Still another company, Applied Spine Technologies (New Haven, Connecticut), is developing what it terms a “less invasive” alternative for patients currently offered fusion or disc replacement. Its AST device for treatment of chronic low back pain is a posterior “flexible stabilization” system to support an injured or degenerated spine while preserving spine motion and flexibility. It requires no tissue removal or replacement.

In the above-mentioned November panel meeting, Guyers’ colleague at TBI, spine surgeon Barton Sachs, MD, noted what will distinguish these devices from one another in a potentially crowded field: “The disc that differentiates itself, that allows for revision surgery, that can go in more minimally invasively, will have a competitive advantage.”

Toselli said that the next big R&D step towards a more biological solution for degenerative discs is range-of-motion enhancement – what the Charit is designed to do.

“As we start to move from fusion to motion, and as we start to feel that preserving motion is a good thing in the spine, I think the next logical step would be to try to continue to evolve motion products, next generation discs as well as nucleus replacement devices.”

He noted that as medicine continues to rearrange the continuum of care – meaning, treating patients earlier in disc degeneration to improve long-term, “Then I think you start talking about the ultimate solution being a biological one.”

While declining to estimate specific adoption rates for these devices, Toselli predicted an increase over time in their use if physicians and patients continue to report positive experiences with them. And he believes patients will ultimately push for technologies that don’t fuse the spine.

“I think it’s up to the company and the surgeon in partnership to define the responsible way to apply the technology.”