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Metal on Metal Hip Implants Face Stronger Regulation by FDA




Metal-on-metal (MoM) hip implants are more or less accepted as a risky choice due to their tendency to deposit miniscule metal fragments into the bloodstream. According to the U.S. Food and Drug Administration’s (FDA) explanation, over time, the metal particles around some MoM implants can cause damage to bone and/or tissue surrounding the implant and joint. This often is called an adverse local tissue reaction (ALTR) or adverse reaction to metal debris (ARMD).

Because MoM implants were marketed in the United States before the 1976 legislation that gave the FDA premarket authority over medical devices, they were classified as “preamendment devices.” Therefore, they were designated Class III (higher risk) devices but remained regulated under the 510(k) premarket notification program. On Jan. 17, the FDA issued a proposed order requiring manufacturers of MoM total hip replacement systems to submit premarket approval (PMA) applications as opposed to 510(k) clearance applications.

The FDA also released an updated report on MoM hip implants which specifies that the implants can cause soft-tissue damage and pain, possibly prompting additional surgery. The report is based on reviews of new published literature and the results of a June 2012 Orthopedic and Rehabilitation Devices Advisory Panel meeting. According to the report, soft tissue damage may lead to pain, implant loosening, device failure and the need for revision surgery (a surgical procedure where the implant is replaced). Some of the metal ions (commonly cobalt or chromium) released enter the bloodstream and travel to other parts of the body, where they may cause symptoms or illnesses. The FDA, however, added a caveat—there is not sufficient scientific data to specify exactly how high the level of ions need to be to trigger adverse systemic effects. Current and recent patients have reacted differently to metal wear particles.

FDA recommends that orthopedic surgeons seriously weigh the benefit-risk profile of using a MoM implant rather than an alternative such as metal-on-polyethylene, ceramic-on-polyethylene, ceramic-on-ceramic or ceramic-on-metal. Surgeons are encouraged to inform patients of all risks associated with MoM implants, and to pay close attention to patient populations for which MoM implants are contraindicated.

MoM implant patients with systemic symptoms are more likely to visit their primary care practitioner than their orthopedic surgeon, so the FDA stresses the importance that all health care providers be aware of metal ion adverse events that may occur in metal-on-metal hip implant patients. Based on case reports, these events may include:
  • General hypersensitivity reaction (skin rash);
  • Cardiomyopathy;
  • Neurological changes including sensory changes (auditory, or visual impairments);
  • Psychological status change (including depression);
  • Renal function impairment; and
  • Thyroid dysfunction (including neck discomfort, fatigue, weight gain or feeling cold.
Patients with symptoms that may be related to a metal-on-metal hip implant should be advised to follow up with his or her orthopedic surgeon to determine the appropriate course of action. FDA warns patients to look for symptoms such as pain, swelling, numbness, noise (popping, grinding, clicking or squeaking of the hip), and/or a change in their ability to walk.

The agency launched a website in February 2011 to keep physicians and patients abreast of new information regarding MoM implants and informed about the general risks associated with them.