UPDATE 2-US FDA staff question J&J ceramic-on-metal hip data

* FDA staff: New hip did not reduce ion production

* Panel to decide Tuesday whether to recommend approval

* J&J shares close down 0.4 pct (Adds FDA comments, details on rivals; Updates shares)

WASHINGTON, Aug 14 (Reuters) - A new type of Johnson & Johnson JNJ.N hip replacement may not provide a hoped-for advantage over current devices, U.S. reviewers said in documents released on Friday.

The company’s Complete Acetabular Hip System is an experimental ceramic-on-metal implant. No devices of that type are sold in the United States.

Ceramic-on-metal was thought to reduce the production of metal ions that may accumulate in the body. There are concerns that ion accumulation may cause autoimmune reactions or other health problems over the long term.

In a Johnson & Johnson analysis, however, “the ceramic- on-metal ion levels were not statistically different than those determined for metal-on-metal bearings,” Food and Drug Administration reviewers said in an analysis prepared for an advisory panel that meets on Tuesday.

“It would appear from these results that the presumed benefit of the new bearing surface couple ... is limited,” the agency said in a list of questions drafted for the panel.

Concerns have been raised about the long-term effects of ions from metal-on-metal hips, which are not recommended for women of child-bearing age and people with kidney problems.

In J&J’s data, elevated ion levels were seen two years after patients got either metal-on-metal or ceramic-on-metal hips, but “it is unclear if the levels to which they are raised are of clinical significance,” FDA staff said.

“Future data collection that looks at longer term metal ion levels, in both (groups), is of major interest and possible concern,” the agency staff said.

The FDA reviewers said the J&J device did work as well as a metal-on-metal hip in a company study that measured pain, functioning and complications after the implant.

The FDA will ask the panel of outside experts for a recommendation on whether the new hip replacement should be approved. The agency usually follows its panels’ advice.

A spokeswoman for Johnson & Johnson’s DePuy Orthopaedics unit could not immediately be reached for comment.

The product would compete with artificial hips from companies such as Stryker SYK.N, Zimmer Holdings ZMH.N and Smith & Nephew SN.L.

Shares of Johnson & Johnson, a diversified healthcare company, closed down 0.4 percent at $60.08 on the New York Stock Exchange. (Reporting by Lisa Richwine; editing by Andre Grenon, Bernard Orr)