Federal health advisers on Wednesday rejected an implant from Zimmer Holdings saying it's unclear how effective or safe the device would be for treating a painful spinal condition.

The Food and Drug Administration's panel of outside experts voted 5-1 that Zimmer's titanium Dynesys implant should not be approved to restabilize the spine.

The FDA is not required to follow the group's recommendation, though it often does.

The group of spinal surgeons said Zimmer studies have not clearly shown which patients would benefit from the implant.

"There were conflicting results without adequate explanation," said Dr. John Kirkpatrick of the University of Florida College of Medicine. "I don't think they've put adequate thought into why they found what they did."

The group also had concerns about wear and tear on the device over time.

"I think the panel generally believes this is reasonably safe, however the long-term safety remains to be seen," said panel chair Dr. John Kelly of the University of Pennsylvania.

Warsaw, Ind.-based Zimmer Holdings Inc. has asked the FDA to approve its implant to re-stabilize the spine when vertebrae have slipped loose, causing leg pain and muscle weakness. The device would be used instead of spinal fusion, a surgical procedure that involves fusing vertebrae together, but can often carry complications.

Mason Macenski, Zimmer's director of clinical affairs, concluded his presentation saying the company's data "demonstrated a reasonable assurance of safety and effectiveness," though that wasn't enough to persuade the panel.

A Zimmer study of the device met its goal, showing results at least as good as spinal fusion using the company's older Silhouette implant. Patients implanted with Dynesys showed a 52 percent treatment success rate after two years, compared with 40 percent for Silhouette.

But panelists questioned the durability of the device beyond that time frame. Continued...