A recent favorable study has provided, perhaps, a bit of good news for DePuy Spine (Raynham, Massachusetts), a company that has been the recent subject of several turbulent lawsuits and criticisms regarding its Charité spinal disc technology as of late.

Published in the August edition of Spine, the study shows the mobile-core design of the Charité artificial disc – consisting of two metallic endplates and a polyethylene sliding core — reduces facet loading by more than 50% when placed at or near the center of the disc space, meaning a longer lifespan for the replaced disc.

The Charité disc was first given approval by the FDA in 2004 and has been implanted in several thousand patients in the U.S. and more than 15,000 throughout the world.

It is used for spinal arthroplasty in skeletally mature patients with degenerative disc disease.

The study, “Comparison of Biomechanical Function at Ideal and Varied Surgical Placement for Two Lumbar Artificial Disc Implant Designs,” points out the differences between the mobile-core disc and the fixed-core artificial disc increases facet loading.

Used in the placement study were a 3-D finite element model of an intact ligamentous L4-L5 motion segment, to analyze facet loading of a mobile-core artificial disc, and a fixed-core artificial disc in the L4-L5 motion.

“This finite element study suggests that there is a difference between mobile- and fixed cores when it comes to facet loads,” said Fred Geisler, MD, PhD of the Illinois Neuro-Spine Center (Aurora, Illinois). “Additionally our study predicted much less stress on a mobile core, which may increase its longevity, compared to a fixed core.”

Geisler, along with Missoum Mouemene, PhD, of DePuy Spine authored the study.

The findings show that once the disc is placed centrally, anteriorly, posteriorly, or laterally, it reduced facet load by 60%, 50%, 85% and 60%, respectively, in axial rotation. The fixed-core disc increased facet load when placed centrally, anteriorly and laterally by 4%, 12% and 10% respectively, and lessened the facet load in axial rotation only when placed posteriorly.

“This finite element study suggests that the mobile-core disc design appears to be less sensitive to the placement because of its ability to shift side-to-side posteriorly and anteriorly as loads are applied, effectively providing a better load-sharing environment between the major restraints, the facets, and the artificial disc itself,” Mouemene said.

The company, a business of Johnson & Johnson (New Brunswick, New Jersey), recently has garnered attention and negative med-tech headlines — as has the entire lumber artificial disc sector. During the 2007 meeting of the American Association of Neurological Surgeons (AANS; Rolling Meadows, Illinois), lumbar disc replacement was called “a critically acclaimed success, but ultimately, a box office failure.”

In a Feb. 15, 2006, decision memo, a team of administrators at the Centers for Medicare & Medicaid Services, acknowledged that they didn’t consult with the Medicare Coverage Advisory on the matter, but 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 to net health benefit.”

The company’s legal affairs have had ups and downs.

The company was successful in its patent infringement case vs. Medtronic (Minneapolis) the court ordered ordering Medtronic to pay $26 million in damages to DePuy. (MDD April 4 2007.) The court found that Medtronic’s MAS screws — used surgically to correct spinal defects —infringed on the Depuy patent.

But in April a Massachusetts superior court judge, dismissed efforts by the company to throw out four lawsuits filed by patients claiming DePuy’s Charité artificial disc is defective (MDD, April 16, 2007). The company argued that it should be protected from the legal action since the FDA approved the device.

On June 21 of this year, the court agreed with DePuy and dismissed all but one of the plaintiff’s claims, stating that “claims alleging a defective design, failure to warn, inadequate labeling of a Class III PMA-approved device are preempted.”

DePuy Spine said it would vigorously defend against this one remaining claim and provide evidence to dispute the allegation.

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