The Food and Drug Administration's panel of outside experts says Zimmer studies have not clearly shown which patients would benefit from its titanium Dynesys implant. The group also has concerns about wear and tear on the device over time.

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

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