Metal-on-metal hip implants can cause soft-tissue damage that may lead to pain and the need for more surgeries, a U.S. regulator said in updating information for patients and surgeons.

The U.S. Food and Drug Administration recommended that patients be informed of the benefits and risks of metal-on-metal hip implants, including that the implant may need to be replaced.

Patients should be told of the risk that their metal-on-metal hip replacement may need to be replaced. (Tom Gannam/Associated Press)

When the metal ball and metal cup in the implants can rub against each during walking or running, metal can be released from the parts that may cause damage to the bone and soft tissue surrounding the implant and joint, the FDA said.

"Metal-on-metal hip implants have unique risks in addition to the general risks of all hip implants," the FDA said on its website.

Authorities in Canada, the U.S. and the UK have warned full metal-on-metal hip implants may be more likely to fail and can cause tissue damage around the joint compared with the traditional metal-and-plastic type of implants.

On Thursday, the FDA issued new recommendations on how often all implants patients should receive clinical exams and when to consider soft tissue imaging and metal ion tests for those showing symptoms.

Reports of adverse events include pain, change in position of a component of the implant, allergy and dislocation.

Last year, data from the U.K. and other countries suggested metal-on-metal implants are are more likely to deteriorate, exposing patients to higher levels of cobalt, chromium and other metals.