AAOS Now

Published 6/1/2012
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Katherine Sale

ASTM Examines Best Practices for MoM Hip Devices

Standards group provides forum for developing standardized tests

Although media reports have drawn attention to the adverse local tissue reactions that can develop due to the release of metal ions in individuals with metal-on-metal (MoM) hip implants, little concensus exists on how to diagnose metal sensitivity, what standards should be applied in assessing explanted devices, and whether—or what—serum metal ion levels should be used as potential revision markers. Because generally established standards could help resolve these problems and facilitate research, the American Society of Testing and Materials, International (ASTM) Committee F04 on Medical Devices, recently held a full-day sysmposium on MoM total hip replacement devices.

The symposium was co-chaired by William Mihalko, MD, PhD, chair of the AAOS Biomedical Engineering (BME) Committee; Jack E. Lemons, PhD, of the University of Alabama–Birmingham School of Dentistry; A. Seth Greenwald, DPhil (Oxon), of Orthopaedic Research Laboratories; and Steven M. Kurtz, PhD, corporate vice president of Exponent, Inc., an engineering and scientific consulting firm.

The symposium provided a forum for consensus development and scientific exchange on the need to standardize and establish best testing practices related to MoM hip replacement devices. The 22 papers and 14 posters focused on the following four areas:

  • Characterization of adverse local tissue reactions
  • Wear/corrosion: Metallic product measurement in fluid and tissue samples
  • Analyses of retrieved MoM implants
  • In vitro testing of MoM implants under adverse conditions

Four sessions, full day
After a report on the prevalence of MoM bearing use in the United States, Dr. Mihalko shared results from a 2010 AAOS survey on bearing surface preferences among AAOS fellows. Lessons learned from adverse event reports, a review of causes and early failures, a systematic review of one company’s MoM products, and data from Medicare patients followed.

Session II covered metal ion assessment, methods for isolating and characterizing wear debris, and correlates of metal hypersensitivity with reported pain in patients. A poster session, necessitated by the overwhelming response to the call for papers, followed. Sessions on retrieval analysis, including the need develop standard for the assessment of explanted devices, and on pre-clinical assessment, with a particular focus on methods of evaluating wear, closed the day-long symposium.

Information from these sessions will shape standards and guides from various subcommittees as they work to develop consensus documents to assist with the terminology, assessment, and characterization of key elements in MoM device wear. The program and abstracts from the symposium were submitted to the U.S. Food and Drug Administration (FDA) as comments in advance of the upcoming Orthopaedic and Rehabilitative Devices Panel meeting on MoM hip devices.

Implant labels
The committee also held an extended session to discuss the draft standard for implant labeling. Kent J. Lowry, MD, a member of the BME committee, has championed the creation of this standard for more than 3 years, based on his concern for patient safety and his frustration with the variations in labeling total joint device components.

Dr. Lowry has developed a draft standard, which is under review by ASTM members. The biggest hurdle to the approval of the standard is concern from the manufacturing community over the impact the standard might have on existing label requirements, such as those mandated by the FDA. The pending finalization of unique device identification requirements from the FDA and uncertainty over the accompanying implementation schedule presents further challenges.

Members of the BME committee attended to support Dr. Lowry’s efforts and will continue to advocate for the adoption of the standard.

A workshop on issues surrounding the use of platelet rich plasma is tentatively scheduled for May 2013.

A link to the MoM abstract submissions to the FDA can be found here.

Katherine Sale is manager, biomedical research and regulation, in the AAOS department of research & scientific affairs. She can be reached at sale@aaos.org

About ASTM and Consensus Standards
Consensus standards for orthopaedic device systems are based on mutual agreements reached by all stakeholders, including users (medical professionals and hospitals), developers/producers (manufacturers) and general interest groups (academia, regulators and patient-oriented participants). Consensus standards serve as fundamental reference documents for product quality.

The ASTM Committee F04 on Medical Devices develops orthopaedic device standards for the United States as well as for international considerations. Voting on proposed standards is monitored by stakeholders to obtain even, unbiased representation. The consensus process requires that all negative votes be resolved or categorized as “nonpersuasive” by the overall F04 membership.