The U.S. Food and Drug Administration (FDA) is advising patients, caregivers, and healthcare providers about the higher than expected risk of the polyethylene (plastic) component of the device breaking (fracture), as early as three to four years after implantation in all Scandinavian Total Ankle Replacement devices (STAR Ankle). Fracture of the plastic component of the STAR Ankle may lead to surgery to repair or replace the device.
Based on the FDA’s recent analysis of FDA-required post approval studies and adverse event reports, the potential risk of the plastic component breaking may exist for all STAR Ankle devices, regardless of the date of manufacture or distribution.
The FDA believes the STAR Ankle remains appropriate for certain patient populations, such as older patients with lower activity levels. Based on the additional medical literature and real-world evidence, patients with more active lifestyles, osteoarthritis (disease where the protective joint tissue breaks down and causes pain and swelling), or age younger than 55 years old may have a higher than expected risk of the plastic component breaking. The FDA is providing the recommendations below to help patients and healthcare providers monitor for signs of possible fracture of the plastic component in the STAR Ankle.
Surgeons should closely monitor patients with the STAR Ankle for potential fractures of the plastic component of the device. If surgeons suspect a fractured plastic component (for example, there is pain or noise from the device), consider performing X-rays to further evaluate the device integrity. Changes on X-rays can be subtle; if X-rays are negative and a polyethylene fracture is still suspected, a CT scan may be needed to determine whether a plastic component fracture has occurred. Be aware that the clinical presentation (the presence of signs or symptoms) of fracture in plastic materials such as polyethylene can be subtle even in a CT scan and, infrequently, may be diagnosed only on exploratory surgery.
The STAR Ankle is indicated for use as a non-cemented total ankle prosthetic (“artificial joint”) and used to replace a painful arthritic ankle joint due to osteoarthritis, post-traumatic arthritis, or rheumatoid arthritis. The STAR Ankle, which is comprised of a tibial plate, a mobile-bearing polyethylene component, and a talar component, is designed to allow for some of normal ankle mobility and function. The mobile-bearing device component is made from sterilized polyethylene.
Based on the results of the long-term post-approval study, the plastic component fractured at a cumulative rate of 13.8% (12/87) at eight-year post-implantation, with all fractures requiring additional surgery. Fractures were also observed as early as three to four years after implantation, which was unexpected. This higher fracture rate and earlier than expected occurrence are concerning when compared with other comparable total ankle replacement devices and may also be underestimated as two polyethylene fractures were not diagnosed until surgical exploration in this study. The concern about fracture rate in the post-approval study has been previously acknowledged and communicated by the device manufacturer. However, Stryker’s (manufacturer of STAR Ankle) communication excluded devices manufactured after Aug. 1, 2014, when changes were made in the inner-pouch foil packaging to limit the material degradation of the polyethylene component.
Given the long-term post-approval study only included patients implanted before the packaging change, the FDA evaluated available post-market data (for example, adverse events in medical device reports) to assess the potential for fracture of the plastic device component to occur in patients with the devices manufactured after the packaging change. Since 2009, at least 1,841 adverse event reports have been received for the STAR Ankle. The FDA concluded that about 300 of these reports described events of fractured plastic components and included STAR Ankle devices manufactured before and after the 2014 packaging change. Of note, although the MDR system is a valuable source of information, this passive surveillance system has limitations, including incomplete, inaccurate, untimely or biased data in the reports. In addition, the incidence or prevalence of the plastic fracture cannot be determined from this reporting system alone due to potential under-reporting, duplicate reporting of events, and the lack of information about the total number of patients with the implants.
In addition, the FDA reviewed data provided by the manufacturer on 244 STAR Ankle implants that were removed (including devices manufactured after the 2014 packaging change), which showed 72 plastic component fractures. Fractures were observed more frequently in thinner plastic device components (6mm thickness) as opposed to thicker components (7mm-9mm), with only one fracture observed in the 11-14mm thickness range. Most of the plastic component fractures showed material oxidation degradation after three to four years of implantation and exhibited loss of mechanical properties. However, the FDA does recognize that the sample size of the removed implants with plastic component fractures was small (n=72).
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 FDA continues to work with Stryker to better understand the factors which contribute to the plastic component fracture based on results from post-approval studies and other data sources. The FDA will also continue to review medical literature, real-world evidence, FDA-required post approval studies, adverse event reports, registry data, and information from patients, healthcare providers, orthopedic professional societies, and the manufacturer.
