FDA on Metal Metal Implants
Follow-Up for Metal-on-Metal Hip Patients Developing Local Signs/Symptoms
Clinical and Imaging Evaluation
If you have a patient with the presence of local symptoms such as pain or decrease in joint function that appear more than three months after metal-on-metal (MoM) hip implant surgery, you should conduct a thorough evaluation.
- Guide your clinical evaluation by the symptoms and physical findings, including an assessment for well-known emergent complications including joint infection, implant loosening, peri-prosthetic fracture and dislocation.
- Recognize that localized lesions associated with reactions to metal debris may also present with pain or a variety of other signs/symptoms including:
- Local nerve palsy
- Palpable mass
- Local swelling
- Joint dislocation or subluxation
- Consider using diagnostic imaging procedures as part of the evaluation noting the following:
- The risks and benefits of using different types of diagnostic imaging procedures should be considered when determining the most appropriate imaging modality.
- FDA guidance recommends that labeling for an implant without a source of electrical energy (passive implant) address its safety and compatibility in a magnetic resonance (MR) field. Check the device-specific labeling for this information.
Metal Ion Testing
- If metal ion (e.g. cobalt and chromium) levels are assessed, interpret the values in the context of the overall specific clinical scenario including symptoms, physical findings, and other diagnostic results when considering further actions. If clinical and imaging evaluations lead to the suspicion of an adverse reaction to metal debris (e.g., soft tissue mass), consider assessing and monitoring serial metal ion levels.
- Increases in metal ion levels over time may be suggestive of significant and/or continuing device wear which may lead to failure of the device requiring revision.
- When assessing metal ion levels, it is important to determine if the patient has any other reasons to have elevated levels including:
- Other implanted metal hardware
- Occupational exposure
- Renal insufficiency
- Dietary supplements
- Despite the recommendations of other international regulatory agencies, the FDA currently believes there is insufficient evidence to correlate the presence of localized lesions, clinical outcomes, and/or the need for revision with specific metal ion levels for individual patients.
- Although there are currently no commercially available standardized tests to assess metal-ion levels, there are a few laboratories in the U.S. that are able to perform these analyses.
- Consult with your normal test laboratory to determine if they are able to conduct metal ion testing, and if so, how specimens should be collected.
- Metal ion testing using whole blood versus serum will give different results. When following serial levels in a particular patient, ensure the same metal ion testing method is used each time for the analysis.
- Note that FDA does not regulate tests that are individually developed and used only in a single laboratory.
Assessment for Systemic Effects
- Patients with evidence of excessive device wear or a localized adverse reaction to metal debris (ARMD) should also be assessed for potential systemic effects of exposure to metal ions. Although only a few case reports in the literature describe potential systemic effects of metal ions associated with metal-containing hip implant systems, a thorough physical examination should be performed with particular focus on cardiovascular, neurological, renal and thyroid signs/symptoms.
- Because metal ions are cleared through the kidneys, a patient who has renal insufficiency may be at higher risk for systemic adverse events.
- There are currently insufficient data to identify any specific numerical values for blood metal ion levels that would cause or correlate with adverse systemic effects for an individual patient.
- Evaluate patients with new systemic symptoms in collaboration with their primary medical physicians or specialists to determine the cause of their symptoms or findings.
- At this time, there is insufficient scientific data to provide a rigorous science-based recommendation for a threshold value of metal ion levels in the blood that would serve as a trigger for intervention or revision.
- The decision to revise a patient's MoM hip implant should be made in response to the overall clinical scenario and results of diagnostic testing.
- If you recommend revision, advise patients of the surgical risks of revision as well as the expected outcomes including the potential need for a future revision procedure.
- When possible, contact the manufacturer prior to revision surgery for instructions on returning the implant for analysis.
- A retrieval analysis will be most informative in those cases where there is no obvious cause for implant failure such as malposition, or likely risk factors.
- long with the implant, provide non-identifying information about the patient, the date of procedure, observations from the revision surgery and the histopathology report from any tissue sent to the hospital pathologist.
- Report any adverse events believed to be related to the MoM system to FDA through MedWatch, the FDA Safety Information and Adverse Event Reporting Program2.
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