Natural-Knee II System metal-backed patella - used in knee replacements

Related information

Hazard alert - risk of premature implant failure

26 March 2014

Consumers and health professionals are advised that Zimmer, in consultation with the TGA, has issued a hazard alert regarding its Natural-Knee II System metal-backed patella. Zimmer has also recalled unused stock of a small subset of these devices, specifically those distributed between March 2011 and November 2013.

Natural-Knee II System is an implantable medical device used in knee replacements, which comprises various components, including a femoral component, a tibial component (also known as the tibial baseplate), a patella button and a tibial insert. The metal-backed version of the patella button is the only component affected by this hazard alert.

metal-backed patella, showing the polyethylene surface and metal back

Figure 1 - Metal-backed patella

It has been identified that in a small subset of Natural-Knee II System metal-backed patellas there is a risk of premature implant failure.

An investigation of a single complaint of discolouration of the polyethylene surface of a non-implanted metal-backed patella revealed oxidation caused by prolonged exposure to artificial light, which occurred during a delay in packaging. This issue potentially affects 20 metal-backed patellas that have been implanted in Australia.

Increased oxidation levels could potentially result in increased wear and damage of the polyethylene surface of a metal-backed patella. If this occurs, revision surgery may be necessary to replace the metal-backed patella and any other components that may have been affected by the increased wear.

As of 17 March 2014, no patient injuries have been reported as a result of discolouration or increased oxidation.

Zimmer has updated its storage process to prevent occurrence of this issue in the future.

Information for consumers

This issue potentially affects 20 metal-backed patellas that have been implanted in patients in Australia.

Zimmer has written to surgeons who have implanted these devices, providing further information about the above issue.

If you have any questions or concerns, please contact your surgeon or the hospital where the surgery was undertaken.

Information for all health professionals

If you are treating patients who have had a knee replacement and are concerned about the above issue, reassure them that the likelihood of them experiencing related problems is very low.

Patients who continue to have questions or concerns about this issue should be referred to their surgeon or the hospital where the surgery was undertaken.

Information for orthopaedic surgeons

Zimmer has written to surgeons who have implanted Natural-Knee II Systems including metal-backed patellas from the affected batches, providing further information about the above issue.

Zimmer has already quarantined all unused stock and will return it to the manufacturer.

If you are treating a patient who received a potentially affected device, it is recommended that you continue your normal post-operative follow-up routine.

If you have any questions or concerns about this issue, contact Zimmer.

Reporting problems

Consumers and health professionals are encouraged to report problems with medical devices. Your report will contribute to the TGA's monitoring of these products. For more information see the TGA Incident Reporting and Investigation Scheme (IRIS).

The TGA cannot give advice about an individual's medical condition. You are strongly encouraged to talk with a health professional if you are concerned about a possible adverse event associated with a medical device.