The US Food and Drug Administration (FDA) is advising patients, caregivers and healthcare providers about the higher-than-expected risk of polyethylene component breakage in all Scandinavian Total Ankle Replacement (STAR Ankle) devices.

STAR Ankle was originally manufactured by multinational medtech firm Stryker, but the product was divested to DJO in November last year.

The plastic components in the devices are breaking as early as thee to four years after implantation.

All patients whose STAR devices have fractured have required additional surgery to replace or repair the device.

Based on the FDA’s analysis of post-approval studies and adverse event reports, the risk of the plastic component breaking may exist for all STAR Ankle devices, regardless of manufacture or distribution date.

A long-term post-approval study found that the plastic component fractured at a cumulative rate of 13.8% eight years post-implantation.

Fractures were observed as early as three to four years after implantation, a finding the FDA described as “unexpected”.

The concerns about fracture rate in the post-approval study have already been acknowledged by Stryker, but the firm’s communication excluded devices manufactured after 1 August 2014 when changes were made in the inner-pouch foil packaging to limit the material degradation of the polyethylene component.

The FDA evaluated available post-market data to assess the breakage rate of devices manufactured after the packaging change, and found that of the 1,841 adverse event reports made about STAR Ankle since 2009 about 300 described fractured plastic components produced before and after the packaging change.

The FDA also reviewed data provided by Stryker on 244 STAR Ankle implants that were removed, 72 of which showed plastic component fractures.

The fractures were observed more frequently in thinner device components of 6mm thickness, as opposed to 7mm to 9mm thickness, with only one fracture observed in the 11mm to 14mm thickness range.

Most of the 72 plastic component fractures showed material oxidation degradation after three to four years of implantation and exhibited loss of mechanical properties.

In a public statement, the FDA said: “The FDA considers plastic component fractures in the STAR Ankle may be attributed to multiple factors, including device design (component thickness), material (degradation), surgical factors and patient factors (such as younger patients with higher activity levels).

“Therefore, while the long-term fracture rate is not known in devices manufactured after the 2014 packaging change, all patients who have the device implanted or are considering getting the device should be aware of the risk of plastic component fracture, which may subsequently require re-operation.”

The agency said the STAR Ankle device remains appropriate for certain patients, such as older people with lower activity levels.

However, patients with more active lifestyles, those with osteoarthritis and those who are aged less than 55 may have a higher-than-expected risk of the component breaking.