The US Food and Drug Administration (FDA) has issued 145 orders for postmarketing surveillance studies to 21 manufacturers of metal-on-metal (MoM) hip replacement systems.

The FDA is authorized to require a manufacturer to conduct postmarketing surveillance of a device if its failure would be reasonably likely to have serious adverse health consequences, it is expected to have significant use in pediatric populations, it is intended to be implanted in the body for more than 1 year, or it is intended to be a life-sustaining or life-supporting device used outside a device user facility.

In this case, the FDA states that they are concerned about potential problems with the device, including loosening, adverse local tissue reactions, and increased metal ion concentrations in the blood.

The manufacturers will be required to submit a research protocol to the FDA that addresses specific safety issues related to these devices.

Data in the published literature, along with reports submitted to the FDA, indicate high blood ion concentrations of the metals used in the device; it is currently unclear whether this could lead to adverse events such as increased pain or need for revision.

At this time, there are not enough data available to conclusively link increased metal ion concentrations of cobalt and chromium to rates of adverse events associated with MoM hip replacement systems, the FDA notes.

The manufacturers must submit a plan to conduct market surveillance within 30 days of the order, and the research protocol must address safety issues related to these devices. Specific questions to be addressed include:

• What adverse events have been observed in patients with MoM total hip replacement systems, and what are the rates of expected (included in labeling) and unexpected adverse events?
• What are the baseline serum and whole-blood levels of chromium and serum or whole-blood levels of cobalt in patients before receiving the device, and do these average levels increase over a minimum of the first 8 years (or length of time on market) postimplant?
• What are the reasons for revision?
• Among patients who do not have a revision, what is the incidence of pain or functional symptoms?
• What demographics or patient selection criteria are associated with higher metal ion concentrations?
• What are the modes and causes of failure based on analysis of all of each company's reasonably available explanted retrieved devices?

The FDA encourages patients who have received these devices to contact their orthopaedic surgeon immediately if they develop new or experience a significant worsening of symptoms or problems 3 or more months after their MoM system was implanted. The FDA also urges patients with MoM hip replacement systems to participate in these studies if contacted by MoM sponsors or their clinician.

More information about postmarket surveillance studies also available on theFDA Web site.

Roxanne Nelson • Medscape Medical News © 2011 WebMD, LLC