The U.S. Food and Drug Administration (FDA) this week issued a warning about certain types of hip implants. Metal-on-metal implants have been found to cause soft tissue damage, leading to pain or the failure of the device.

The devices, made of cobalt-chromium-molybdenum alloys, slide against each other when patients walk or run using them. With enough of that sliding, small bits of metal particles can wear off the cup or other parts of the implant where components connect. The particles can then cause damage to soft tissue and bone around the implant and joint.

In addition to the pain caused by what doctors call an “adverse reaction to metal debris” (ARMD), the process can loosen the implant. In extreme cases this can cause the hip implant to fail, meaning more surgery would be required to replace it.

The FDA also stated that metal ions can be released into the bloodstream, traveling to other parts of the body where they can cause symptoms or illnesses. However, reactions to the metal wear particles seem to be specific to patients, and the FDA does not have enough data to say just how high the concentration of metal ions is in a patient’s body.

As a result of the warning, the FDA is recommending that surgeons consider alternative hip implants, such as metal-on-polyethylene, ceramic-on-polyethylene, ceramic-on-ceramic, or ceramic-on-metal, depending on a patient’s age, sex, weight, diagnosis, and activity level. It is also recommended that patients with metal-on-metal hip implants receive yearly or biyearly physical exams and radiographs.