FDA device panel backs artificial lumbar disk: success and satisfaction rates with the disk, long used in Europe, surpassed those with a fusion device.

GAITHERSBURG, MD. -- The first-ever artificial spinal disk cleared a significant hurdle with the unanimous backing of the Food and Drug Administration's Orthopedic and Rehabilitation Devices Panel.

The panel voted 8-0 for conditional approval of the Charite artificial disk. The device, which consists of two metal alloy endplates sandwiched over ultra-high-molecular-weight polyethylene, will be indicated for use in patients who have degenerative disk disease at one level from L4 to S1, with up to 3 mm of spondylolisthesis at the involved level. Charite is manufactured by Waldemar Link GmbH & Co. in Hamburg, Germany, and will be sold by Johnson & Johnson's DePuy Spine Inc. division.

The FDA usually follows the nonbinding advice of its panels.

Theoretically, Charite will be an alternative for many of the 200,000 Americans who undergo lumbar fusion each year. DePuy hopes it will also help prevent adjacent disk disease since, unlike a fusion, it will not create pressure on adjacent levels.

"The concept with an artificial disk is to prevent that sequence of events, so you don't see people with multiple levels of lumbar fusion trying to chase this disk pain," said Dr. John Kirkpatrick, a panelist and orthopedic surgeon at the University of Alabama, Birmingham.

But Dr. Kirkpatrick initially motioned against approval, questioning whether the company's 2 years of follow-up were sufficient. Other panelists voted down the motion, arguing that there was a long history of use in Europe. And some said that voting against approval would perhaps stymie innovation and punish American patients.

"We are the only country in the industrialized world that does not approve its use yet," argued committee member Dr. Fernando G. Diaz, a neurosurgeon at Detroit Medical Center.

According to DePuy, Charite is sold in 30 countries and has been implanted in 7,000 patients worldwide since 1987.

Despite that history, the panel heard public testimony about occasional device malfunctions and serious adverse events. As a condition of approval, panelists urged DePuy to follow the patients in a study for an additional 2 years, which would effectively provide 5 years of follow-up on patients who enrolled in 2000. The panel also called for further durability testing and said that DePuy should somehow ensure that surgeons are well trained in implanting the Charite. To aid tracking in the case of a recall or malfunction, the committee said that patients implanted with Charite should be given an index card with the name and manufacturer of the device, its lot number, and the names of the surgeon and hospital.

DePuy aimed to show that Charite was not inferior to the BAK Interbody Fusion Device for the treatment of single-level degenerative disk disease at L4/L5 or L5/S1. The FDA reviewers agreed that Charite had exceeded that expectation.

A total of 205 patients at 15 sites was randomized to Charite and 99 to BAK. The mean age in both groups was 40 years, and 70% in each group had disease at L5/S1. Patients were eligible for the study if they had symptomatic disease shown by CT or MRI scan and confirmed by diskogram, had failed 6 months of conservative treatment, had achieved a score of 30 on the Oswestry low back pain disability questionnaire, and were candidates for the anterior approach.

The patients could have leg or back pain, but only in the absence of nerve root compression. Those with previous surgery at any level were excluded unless they had had a diskectomy, laminotomy, laminectomy, or nucleolysis at the same level.

Success was defined as improvement of more than 25% on the Oswestry questionnaire at 24 months; no device failures requiring revision, reoperation, or removal; absence of major complications such as vessel injury, neurologic damage, or nerve root injury; and maintenance or improvement in neurologic status at 24 months, with no permanent neurologic deficits compared with baseline.

According to the FDA, the overall success rate was 63%-68% for Charite, compared with 48%-54% for BAK. Satisfaction rates were also higher for Charite patients; at 2 years, 73% of Charite patients and 55% of fusion patients were satisfied, and 12% of Charite and 19% of BAK patients were dissatisfied or somewhat dissatisfied.

FDA reviewers noted that although Charite relieved pain in many patients, 14% had either no pain relief or a worsening, and 13% had only partial relief. The ongoing pain is hard to explain, but it could come from facet joint degeneration, they said.

The panel was not concerned, noting that there is usually no clear explanation for back pain. "Assessing pain is like trying to pin jello on the wall," Dr. Diaz said.

Adverse events were common, affecting 76% of Charite patients and 78% of BAK patients. Half of the patients experienced pain in the back or lower extremities, but only 5% in the Charite group and 2% in the BAK group attributed their discomfort to the devices.

The infection rate was 12% in the Charite group, compared with 6% in the BAK group.

Panelists' main safety concern was the potential for revisions. Some of them were uncomfortable with Charite's wear testing and uncertain about its lifespan.

Several surgeons testified in the open hearing that Charite was flawed and would lead to revisions. All had their travel paid for by Medtronic Inc., a leader in fusion-related instrumentation that is developing a rival artificial disk. The most vocal critic, Dr. John Peloza, a spine surgeon from Dallas, said a second anterior approach presented the potential for life-threatening complications.

Charite lead investigator Dr. Paul McAfee, chief of spine surgery at St. Joseph's Hospital in Towson, Md., agreed that second surgeries would be risky. But he also said that patients would most likely receive a fusion, not a replacement Charite, unless the disk had malfunctioned.

BY ALICIA AULT

Contributing Writer