Lassoing Medtronic's Maverick

The company says its new disc has a twist that makes it better.
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Two spine experts, hoping to relieve patients of crushing lower-back pain, have posed opposing theories about the fate of artificial lumbar discs.

Charles Rosen, a university-based spine surgeon with no ties to industry, insists that all of the discs being sold now rely on a flawed design that essentially dooms them to fail. But Hal Matthews, a prominent research surgeon and paid consultant for

Medtronic

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, insists that Medtronic's new Maverick disc -- when implanted correctly in the right patients -- should suffer no mechanical failures at all.

If Rosen's radical theory proves correct, dozens of artificial discs could be rendered obsolete, sending massive investments and a crucial new market opportunity down the drain. But if Matthews is right, lumbar discs could gain traction and emerge as one of the biggest advances in the history of spine surgery.

Moreover, the Maverick could prevail as the disc of choice over competing devices manufactured by

Johnson & Johnson

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and Synthes that have weathered failures already.

With the Maverick, "you've got a good thing that's going to have a really hard chance of failing," Matthews says. "It's like that perfect tire that won't ever have to be changed."

But Rosen views such claims with astonishment.

"There is no device in medicine that can't fail," he insists. "At some point in time, they all have. What a crazy thing to say."

Scientific Debate

Some industry experts view Rosen as the crazy one, though.

Rosen has proposed that all lumbar-disc makers have somehow misjudged the biomechanics of the spine and made the same mistake. Specifically, he claims, they have wrongly assumed that the spine's center of rotation lies in front of the spinal canal, when it actually lies behind. As a result, he says, the discs cannot possibly function as designed.

The government-funded orthopedics biomechanics laboratory at the University of California at Irvine, where Rosen is based, has launched a new study in an effort to show how the spine naturally works and whether artificial discs can help that process.

Matthews insists that they can. And, based on his credentials, he should certainly know.

Matthews has long focused on motion-preservation devices, serving as a director and charter member of the professional society for disc-replacement surgeons. He says he fielded offers to help out with studies of the ProDisc -- a Synthes device that should hit the market soon -- but held out for the Maverick trials instead.

Matthews performed the first-ever disc replacement using the Maverick in early 2002. He then went on to lead studies of the Maverick in what he describes as the biggest artificial-disc trial ever.

So far, both J&J and Synthes have offered clinical evidence that their discs work as well as fusion surgery. But Matthews' group hopes to show that Mavericks statistically outperform the procedure. Matthews portrays the success rate as high -- and the failures as virtually nonexistent -- in patients who have received Mavericks through clinical trials so far.

Those trials have now been completed. The final results should be collected by the end of the year, opening the door for regulatory approval down the road.

Matthews has seen the favorable outcomes with his own eyes.

"It's quite simple," he says. "A fusion patient walks into my office very tentatively and sits down very slowly. ... A disc-replacement patient jumps up and shakes my hand."

Matthews favors the Maverick for several reasons.

For starters, he says, the device features a simple design that's easy for surgeons to use and patients to understand. It also stands out as the only disc made entirely of metal, he says, promising the durability to last a lifetime. Finally, he adds, it boasts favorable biomechanics because it is placed in "the closest location to the physiological center of rotation" in the spine.

The Maverick, like other lumber discs, winds up in front of the spinal canal. Matthews disagrees with Rosen's notion that the spine's center of rotation clearly lies elsewhere.

"The center of rotation actually changes," he says, citing a 2001 study published by

Spine

.

Torn Ligament

That study, carried out by researchers at the University of Iowa with support from a company now owned by Medtronic, offers validation for the Maverick in particular.

Specifically, the study makes a strong case for the Maverick's unique placement in the spine. Surgeons insert Mavericks further back than other lumbar discs, but they still place the devices in front of -- rather than behind -- the spinal canal.

Rosen sees major flaws in that study, however. He points to a single sentence, published in the "methods" section of the introduction, as perhaps the most glaring example. There, he says, the authors briefly note that they restored a crucial ligament in the cadavers that they used.

"That ligament is destroyed when you put the disc in," Rosen insists. "You no longer have that ligament as a check to keep the disc from opening up too much and popping out. ... So they've set up a model that's not the way things are."

Moreover, Rosen claims, the authors then offer "made-up reasons" for restoring the ligament in the first place.

In addition, he says, the study fails to address another crucial issue at all. Notably, he says, it never points out that artificial discs cannot absorb shock like the natural discs they must replace.

Matthews readily admits that scientists have no way to duplicate the shock-absorption function of discs. At the same time, however, he questions whether they really need to.

"We're not convinced that it's important," he says. "It may be a luxury. ... Nobody really knows."

Rosen, for one, finds the entire situation incredible.

"It kind of reminds me of 'The Emperor's New Clothes,'" he says. "It's like you say something enough, people start to believe it."