Metal-on-metal hip implants can cause soft-tissue damage and pain, which could lead to further surgery to replace the implant, the U.S. health regulator said, following several recalls of the artificial hip parts.

All-metal hip implants were developed to be more durable than traditional implants but have become a major cause of concern following several safety issues and user discomforts.

The traditional implants combine a ceramic or metal ball with a plastic socket.

The U.S. Food and Drug Administration said all-metal implants can shed metal where two components connect, such as the ball and the cup that slide against each other during walking or running.

Such release of metal will cause wear and tear of the implant and can damage bone and soft tissue surrounding the implant.

The agency said surgeons should select a metal-on-metal hip implant for their patient only after determining that its benefits outweigh that of an alternative hip system.

Johnson & Johnson, the biggest manufacturer of all-metal devices, recalled its ASR hip implant in 2010 following safety problems.

Smith & Nephew withdrew a component of one of its all-metal artificial hip systems last June, following higher level of patient problems with the device. Stryker Corp begun recalling some components of its implant in July due to risks associated with corrosion.

Other hip implant makers include Zimmer Holdings Inc and Wright Medical Group.

The regulator, however, added that it does not have enough data to specify the concentration of metal ions in a patient’s body or blood necessary to produce adverse effects.

The reaction seemed to be specific to individual patients, the FDA said on its website.

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(Reuters)