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FDA orders post-market studies on MOM hip implants

By Jeanie Kennedy and Katherine Sale

On May 9, 2011, the U.S. Food and Drug Administration (FDA) issued orders for postmarket surveillance studies from several orthopaedic device manufacturers of metal-on-metal (MOM) total hip arthroplasty (THA) implant systems. The agency is seeking information on metal ion concentrations and their effects on long-term outcomes for THA patients.

Manufacturers must comply with the FDA order and submit a research plan within 30 days of receiving the FDA letter. The FDA then has 60 days to either approve the protocol or work with the manufacturer to amend the study design. The studies are to last at least 3 years. Manufacturers will need the assistance of some orthopaedic surgeons to accomplish these mandated postmarket studies. Details of the studies are still being formulated and will likely vary among manufacturers.

Key to any analysis of the impact of MOM hips are appropriate and consistent standards for metal ion testing. The American Society for Testing and Materials, International hosted a one-day workshop in Anaheim, Calif., to identify needs for characterization and standardized testing for MOM THA devices. The workshop was cochaired by William M. Mihalko, MD, PhD, who also chairs the AAOS Biomedical Engineering (BME) Committee; Jack Lemons, PhD, and A. Seth Greenwald, D. Phil (Oxon), who have served as consultants to the BME committee; and Steven Kurtz, PhD.

Experts on imaging, retrieval analysis, implant wear, and testing convened to begin establishing best testing practices in the following four areas:

  • characterization of adverse local tissue reactions
  • wear and corrosion: metallic product measurement in fluid and tissue samples
  • analyses of retrieved MOM implants
  • in vitro testing of MOM implants under adverse conditions

More than 100 scientists, industry representatives, and orthopaedic surgeons reviewed current evidence and discussed gaps in testing of MOM devices. AAOS Second Vice-President Joshua J. Jacobs, MD, delivered a keynote address. Key messages from the presentations are reflected in the five areas selected for standards development:

  • magnetic resonance imaging standards assessing wear-induced synovitis
  • standard methods for assessing metal allergy
  • standard histiological evaluation score for bearing materials
  • standard to measure ions in serum and correlation to wear
  • test methodologies to mimic clinical failure modes

Work began on these areas during subsequent subcommittee meetings and a 2012 symposium was proposed.

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Additional Links:

Template of the FDA letter to manufacturers (PDF)

The FDA postmarket surveillance page

The AAOS MOM information page

The AAOS comments to the Senate Special Committee on Aging hearing

June 2011 Issue