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Metal-on-Metal Hip Implants - Information for Orthopaedic Surgeons Regarding Patient Management Following Surgery - For Health Professionals
- Starting date:
- April 11, 2012
- Posting date:
- May 9, 2012
- Type of communication:
- Dear Healthcare Professional Letter
- Medical Device
- Source of recall:
- Health Canada
- Healthcare Professionals
- Identification number:
Health Canada Issued Important Safety Information on Metal-on-Metal Hip Implant Surgery
April 11, 2012
Subject: Important Safety Information for Orthopaedic Surgeons regarding Patient Management Following Metal-on-Metal Implant Surgery
To: Orthopaedic surgeons
Metal-on-metal (MoM) hip implants (both resurfacing and total hip replacements) have been available world-wide for many years.
In recent years, there has been an increase in awareness of pain, implant loosening and significant soft tissue reactions thought to be the result of increased levels of metal (cobalt and chromium) ions in the surrounding joint tissue. Soft tissue reactions can range from fluid collection to more extensive necrotic and "pseudotumor" reactions and can necessitate device revision. A survey conducted by the United Kingdom's National Joint Registry (UK NJR) revealed approximately 14.2% of revised MoM hip implants exhibited soft tissue reactionsFootnote a. This was extrapolated to estimate that the overall incidence of significant soft tissue reactions is between 1 and 9 per thousand MoM hip devices implanted. The reactions are thought to be attributable to two aetiologies: wear-related cytotoxicity and hypersensitivityFootnote b. Reports indicate higher revision rates for MoM hip resurfacing devices with small diameter heads (less than 44 mm) than for those with larger diameter heads (greater than 55 mm). For MoM total hip replacements, larger diameter heads (greater than 36 mm) appear to lead to higher revision rates than smaller diameter heads. The reasons for these trends are not fully understood at this time.
The following factors have been identified for increased risk of soft tissue reactions:
- Female patients
- Patients with components not aligned optimally
- Patients with increased activity levels
- Patients who are severely overweight
- Patients with bilateral implants
Early identification of patients experiencing significant soft-tissue reactions is important in improving the probability of successful secondary outcomes. The following are Health Canada's recommendations with respect to follow-up and diagnosis of patients who have been implanted with a MoM device. They are intended to provide surgeons with the guidance necessary for successful MoM outcomes and to aid surgeons in timely and accurate identification of patients experiencing significant soft-tissue reactions.
Pre-Operative and Intra-Operative Considerations
Surgeons should have the necessary experience to perform MoM hip implantations and be properly trained in the implantation technique and technical aspects of the specific implant to be used. Surgeons should ensure that device components are compatible and should not mix components from different manufacturers' hip systems. Pay particular attention to the angles of inclination and anteversion of the acetabular cup, as this can predispose the patient to early failure. Furthermore, the patient should be made fully aware of the risks and benefits of MoM hip replacement, including the risks of high metal ion levels and soft tissue reactions.
Follow-up and Diagnosis for Symptomatic Patients
A patient with a MoM hip implant that is not functioning ideally may experience the following symptoms:
- Pain in the groin, hip or leg
- Swelling at or near the hip joint
- A limp or change in walking ability or limited range of motion
At more advanced stages, soft tissue reactions may also present with local nerve palsy, palpable mass, and joint dislocation or subluxation. If, beyond 3 months post-operatively, a patient presents with any of these symptoms, a thorough clinical evaluation should be performed.
Health Canada recommends the following approach when diagnosing and treating symptomatic patients with suspected soft tissue reactions.
- Perform investigations to dismiss well-known complications such as joint infection, implant loosening, peri-prosthetic fracture and dislocation.
- Diagnostic imaging, such as MRI with MARS (metal artefact reduction sequences) or ultrasound should be performed
- Consider whole blood or serum tests for cobalt and chromium metal ion levels.
General Considerations Relating to Metal Ion Measures
It is important to ensure that the individual collecting the sample is aware that it is for trace metal analysis and that appropriate standardized collection procedures, including trace-metal-free collection containers, are used in sample collection.
When interpreting metal ion test results, consideration must be given to other potential sources of metal ions (e.g. other metal implants, occupational exposure, renal insufficiency, and dietary supplements).
Metal ion testing using whole blood will give different results from testing using serum. If following serial metal ion levels in a particular patient, ensure the same metal ion testing method (i.e. whole blood or serum) is used each time for the analysis.
As of the date of this publication, there are no Health Canada approved standardized tests to assess metal ion levels. As Health Canada does not regulate test kits that have been developed in-house at a particular lab, the validity of comparisons of data collected from different labs is therefore unknown. It is therefore important to ensure, if possible, that the same lab is used in testing of samples from a particular patient. Further, before choosing a lab to be used for sample analysis, we recommend you request and review their test validation.
Currently there is no consensus relating to a threshold value of metal ion levels in the blood that would serve as a trigger for intervention or correlate with adverse systemic effects for an individual patient. However, the United Kingdom's Medicines and Healthcare products Regulatory Agency (MHRA) has suggested that whole blood levels of either cobalt or chromium ions above 7 ppb (parts per billion), or 119 nmol/L for cobalt and 134.5 nmol/L for chromium, are significant. They suggest that below these levels, significant soft tissue reaction and tissue damage is less likely, leading to a lower risk of implant failure.
In the following scenarios, revision of the implant should be seriously considered:
- Painful hips with a positive MRI for a soft tissue mass
- Positive MRI for soft tissue mass, increasing in size
With all possible revisions of a MoM hip implant, a second orthopaedic opinion should be considered.
Metal ion levels should be recognized as one diagnostic tool, but any decision to revise should be based upon all information at the disposal of the surgeon and the overall clinical scenario for that particular patient. Close follow-up is indicated for patients with high metal ion levels or rising metal ion levels.
Current evidence suggests that soft tissue reactions are rare in the absence of pain and deteriorating function. Asymptomatic patients should be followed up at least annually for 5 years postoperatively. Beyond 5 years, follow-up should be in accordance with locally agreed protocols.
Those patients who are at risk for increased device wear and/or soft tissue reactions should be monitored more closely.
Patient follow-up assessments should include a functional assessment, physical examination for range of motion limitations and asymptomatic local swelling or masses.
If revision is to be performed, Health Canada recommends the following:
- When possible, contact the manufacturer prior to revision surgery for instructions on returning the implant for analysis.
- Along 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 the implant manufacturer and to Health Canada's Health Products and Food Branch Inspectorate (HPFBI). Call the HPFBI Hotline at 1-800-267-9675 for guidance.
Managing marketed health product-related adverse incidents depends on health care professionals and consumers reporting them. Reporting rates determined on the basis of spontaneously reported post-marketing adverse incidents are generally presumed to underestimate the risks associated with health product treatments. Any cases of serious or unexpected adverse incidents in patients with metal-on-metal hip implants should be reported to Health Canada at the following addresses:
Any suspected adverse incident can be reported to:
Health Products and Food Branch Inspectorate
Address Locator: 2003D
Ottawa, Ontario K1A 0K9
Telephone: The Inspectorate Hotline: 1-800-267-9675
The Medical Devices Problem Report Form and Guidelines can be found on the Health Canada Web site.
For other medical device inquiries related to this communication, please contact Health Canada at:
Therapeutic Products Directorate
- Footnote a
United Kingdom Medicines and Healthcare products Regulatory Agency.
Report of the Expert Advisory Group looking at soft tissue reactions associated with metal-on-metal hip replacements. Oct 2010.
- Footnote b
Campbell P, Ebramzadeh E, Nelson S, et al. Histological features of pseudotumour- like tissues from metal-on-metal hips. Clin Orthop 2010;468:2321-7
- The Canadian Orthopaedic Association. Metal-on-metal Articulations: An update following the American Academy of Orthopaedic Surgeons (AAOS) Annual Meeting in San Diego (February 2011) Download PDF Document. Mar 2011.
- The Canadian Orthopaedic Association. Withdrawal of DePuy ASR Resurfacing and XL metal-on-metal bearings - Information for and Advice to Surgeons from the Subsection of Arthroplasty of the COA and the Canadian Orthopaedic Association. Download PDF Document. Nov 2010.
- United Kingdom Medicines and Healthcare products Regulatory Agency. Medical Device Alert: All metal-on-metal (MoM) hip replacements. Download PDF Document (MDA/2010/033). Apr 22, 2010.
- United States Food and Drug Administration. Metal on Metal Hip Implants. 2011.
- Date modified: