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FDA advisory committee: More data, consistent testing needed for metal-containing implants
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The Immunology Devices Panel of the Medical Devices Advisory Committee recently met to provide advice and recommendations to the FDA about immunological responses to metal-containing products regulated as medical devices, including metal-containing implants and dental amalgam.
“Overall, the panel feels that successful outcomes of procedures where devices are implanted in the body are multifactorial and their etiology and success depends not just on the patient, but it depends on the devices, it depends on the surgeon, it depends on the technique used and it depends on a number of mechanical properties of the device in addition to immunological or other such processes,” Raj Rao, MD, chair of the panel and professor at George Washington School of Medicine and Health Sciences, said during the panel.
Patient response to metal-containing implants
In their review, the panel agreed that a local inflammatory or immune response occurs with the use of metal-containing implants, but there is not enough scientific evidence to confirm the occurrence of a systemic immune response.
“Given the clinical anecdotal evidence that we have received as a panel and based on our individual experiences, this may be an area for future study down the road,” Rao said.
The local response and possible systemic response to metal-containing implants may be affected by patient-related factors, according to the panel, including osteoporosis; patient age; gender factors, such as mechanical changes in the bone; and anatomic changes. Rao noted the panel reported possible local factors and systemic immune responses that may be patient specific that may also play a role in an individual’s susceptibility to a heightened or prolonged response to a metal implant.
Similarly, the panel noted device-related factors, such as the extent of wear debris generated by the alloy composition, changes in the microstructure of the implant and in the potential coating of an implant with other substances, that may impact the patient’s response to a metal-containing implant.
“The primary thing the panel feels fairly strongly about and fairly consistently about is that it would be beneficial to get a listing of the specific elemental composition of these devices included on the packaging of each of these devices,” Rao said.
Need for consistent testing
In terms of the status and clinical utility of available diagnostic and prognostic tests, the panel noted the need for consistency in the pre-analytical processing of laboratory tests and the validity of immune response testing either pre-surgically or post-surgically.
“There is a desire to get prospective data on any or all of these tests longitudinally in patients who are selected for joint replacements and implant placement,” Rao said. “The goal is that if we have this information preoperatively and then longitudinally have access to the same information postoperatively for over an extended period of time, that will eventually provide us better information.”
Rao added the panel recommends the involvement of federal agencies, such as the NIH, in the collection of these data in a longitudinal format.
Although the panel noted registries or longitudinal cohorts may be helpful in supplying additional information on metal-containing devices, they added more information may be collected through the study of isolated incidents of failure vs. the population at large. Another area for focus and study includes retrieval studies and tissue and blood testing in patients who have had failures or immune responses, according to the panel.
“The panel generally feels that we need improved pre-clinical testing of devices that are to be placed in the body, especially in terms of corrosion testing,” Rao said. “We have to move beyond just mechanical corrosion testing to electrochemical corrosion testing, as well, and possibly look into the role of biological tissues in speeding up or contributing to corrosion in some way.” – by Casey Tingle
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Disclosure: Rao reports he is a board or committee member for the American Orthopaedic Association, Lumbar Spine Research Society and FDA, and is on the editorial or governing board of Elsevier.