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AAOS Now

Published 1/1/2009
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John S. Kirkpatrick, MD

Keeping up with technology

ASTM workshop provides “the big picture”

As orthopaedic surgeons, we are all too familiar with implant devices that fail. Happily, we are even more familiar with devices that are successful, and improve the lives of our patients by increasing mobility and restoring function. So, we continue to trust that when we reach for an implant, it will meet certain standards of durability, size, and functionality, regardless of the manufacturer.

But today’s technology is rapidly changing the device landscape. New testing techniques and new device requirements must be developed to enable us to use these evolving technologies safely and for the benefit of our patients.

On Nov. 18, 2008, several AAOS members had the opportunity to look ahead and share our insights and recommendations at the ASTM International (previously the American Society for Testing and Materials) workshop on “The future of arthroplasty standards: Planning for the next five years.” Joining me at the workshop were current and past members and chairs of the Biomedical Engineering Committee, including Paul A. Anderson, MD; Michael E. Berend, MD; William M. Mihalko, MD, PhD; A. Seth Greenwald, D Phil (Oxon); and Jack E. Lemons, PhD. They brought clinical relevance and expertise to the program and were integral to the workshop and discussions.

A “joint” learning experience
Hip arthroplasty has been performed for more than 60 years, but spine arthroplasty is a much more recent development. Could lessons from one joint be applied to another? That was the focus of the first session of the workshop, which included clinical examples from practice and retrieval programs and covered spine, knee, and hip arthroplasty.

“How ‘what we’ve seen’ should guide ‘what we test’” reviewed the types of clinical failures we are seeing and related these failures to fundamental principles. This topic was further developed into a systems approach illustrating the complexity of the clinical environment and the interrelationships between one mode of failure to others as well as the interaction of biology on mechanics. Participants agreed that an iterative process should be used to update standards, incorporating new findings related to failures and implant design. The need to concentrate on standards that address more common clinical failures, rather than theoretical concerns, was emphasized.

Testing for the real world
The balance of the workshop addressed “Testing perspective: Experience and future directions—Are we simulating what we need to?” Participants discussed new standards development and revision of existing standards to address deficiencies noted in the clinical failures.

For example, the need to evaluate the results of adverse clinical conditions such as impingement, as well as the need to consider some of the potential mechanical consequences of bone conserving designs and thinner cups, were among the issues considered in the hip engineering session. The session on knee engineering was highlighted by a plea to consider the “extremes” of knee use—such as the effects of deep squat kinematics on wear and implant stresses.

Discussion of mobile-bearing considerations broadened to include the question of whether all implant designs should be tested with the same methods or whether particular design features require alternative testing methods. In the spine testing session, this question was applied to the differences between disk replacements with moving bearings and those involving elastomer designs.

Sharing similarities and successes
By including the three major groups studying arthroplasty, the workshop enabled researchers to identify similar problems and concerns. For example, hip, knee, and spine arthroplasty all require a basic testing method for wear and debris supplemented by additional testing methods to encompass “extremes” in clinical use (such as impingement in the hip, squatting in the knee, and whiplash injury in the spine).

Several areas of new standard development and revision of existing standards were identified and were subjects for agenda items in follow-up during ASTM committee meetings. AAOS members interested in participating in the development of joint replacement standards are welcome and are encouraged to contact the chair of the Biomedical Engineering Committee, Dr. Mihalko, at wmihalko@campbellclinic.com or Katherine Sale, staff liaison, at sale@aaos.org

John S. Kirkpatrick, MD, is a past member of the AAOS Biomedical Engineering Committee. He can be reached at john.kirkpatrick@jax.ufl.edu

Orthopaedic devices and consensus standards
By Jack E. Lemons, PhD

“When I use an FDA-approved device in my patient, what assurance do I have that the device shape, dimension, material and design properties, packaging, cleanliness, and sterility are appropriate for the intended clinical application?”

Consensus standards for orthopaedic device systems are based on establishing mutual agreements among the stakeholders—users, developers/producers, and general interest groups. … Support from the AAOS Biomedical Engineering [and] Biological Implants Committees is instrumental to evolving standards. AAOS participation in the Orthopaedic Device Forum has also contributed to the development and application of relevant orthopaedic standards.

Consensus standards provide fundamental reference documentation for product quality … [they] are recognized within the regulatory approval process for medical products by the U.S. Food and Drug Administration as well as the regulatory bodies of many other nations. This acceptance [ensures] quality and helps to reduce costs while increasing competitiveness for U.S.-based products. Longer term highly successful outcomes for implant-related surgical treatment outcomes can be related, in part, to the standardization process.

The future of orthopaedic surgical products is changing rapidly as new devices are developed … Standards for specification of the basic chemistry and biochemistry, tissue processing requirements, and structural and biocompatibility test methods are being developed to [ensure] consistency, quality, and safety. These standards and related clinical trials combine to ensure the safety and effectiveness of these new products. …

It is critical that all device components comply with established requirements and that applicable and consistent material and design properties relate directly to biocompatibility to ensure safety, efficacy, and effectiveness of the device.