On March 15, 2021, the FDA issued a “Safety Communication” for Stryker Corporation’s Scandinavian Total Ankle Replacement (STAR) device.
The communication noted a “higher than expected risk” of the polyethylene component of the device breaking as early as three to four years after implantation in all STAR devices. Fracture could “lead to surgery to repair or replace the device.”
It wasn’t the first safety concern over the implant. This communication comes after Stryker issued a “Safety Communication” on October 11, 2019 warning of a higher-than-expected risk of polyethylene fracture.
The 2019 safety notice stated the company became aware of data indicating that patients who’d received the STAR implant distributed prior to August 1, 2014, “may experience a higher-than-expected risk of polyethylene fracture due to potential increase in polyethylene oxidation prior to or after implantation and potentially the implant geometry.”
August 2014 is about the same time that Stryker acquired Small Bone Innovations, Inc., (SBi) and STAR from the Viscogliosi Brothers for approximately $375 million.
Additional factors the FDA says that may have contributed to the fractures are “component malalignment, surgeon learning curve, and reduced insert thickness.”
Post-Approval Studies
When the device was granted Premarket Approval (PMA) by the FDA in May 2009, the agency required two post-approval studies to examine the performance and adverse event reports.
The first post-approval study was a long-term (eight years) follow-up of a cohort of patients who were enrolled before the device was approved.
The previous Stryker safety communication excluded devices manufactured after August 1, 2014, when changes were made in the inner-pouch foil packaging to limit the material degradation of the polyethylene component.
The second post-approval study was a new enrollment, prospective, multicenter, single arm two-year study to examine the performance of the device compared to the performance in the first study. The second study included patients with and without the new packaging. Of note, the current FDA communication does not include the results from this second post-approval study due to its short follow-up (that is, two years).
Safety Issues and Patient Selection
It is also important to note that the FDA believes the implant 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.”
Under the new FDA safety notice, the agency stated plastic component fractures in the device might be attributed to multiple issues, including the component’s thickness, the degradation of the material, surgical factors, and patient factors, such as younger patients with higher activity levels.
Fracture Rate
Based on the results of the long-term post-approval study, the FDA found 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 the agency says was unexpected.
“This higher fracture rate and earlier than expected occurrence are concerning when compared with other comparable total ankle replacement devices.” The agency said the fracture rate may also be underestimated as two polyethylene fractures were not diagnosed until surgical exploration in this study.
Adverse Event Reports
Since 2009, at least 1,841 adverse event reports have been received for the device. 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.
The agency cautioned that 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.”
The FDA also reviewed data on 244 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. The agency said it recognized that the sample size of the removed implants with plastic component fractures was small (n=72).
STAR Science and Business History
We’ve been writing about the STAR ankle for some time.
The ankle, developed by Waldemar Link, Germany, was designed in 1978 as a two-component anatomic unconstrained resurfacing ankle prosthesis with congruent parts covering the medial and lateral facet joints. A third component was added later.
Along come the Viscogliosi Brothers, who in 2008, through Small Bone Innovations, acquired the device from Waldemar Link for an undisclosed price.
On June 30, 2014, Stryker Corporation announced a definitive agreement to acquire the company from SBi for up to $375 million. At the time, the STAR was the only FDA, PMA approved, cementless, three-piece total ankle replacement system in the market.
The device, Tony Viscogliosi told us in 2014, was then the most published total ankle replacement product in the world. He noted more than 20 years of clinical history, four evolutions of generations of the STAR technology and more than 26,000 implants and published long-term clinical results with 91% satisfaction and 92% survival rates at 9.1 years.
STAR was the only ankle that was clinically marketed ubiquitously around the world, said Viscogliosi. “No one outside the U.S. uses two-part ankles because those ankles demonstrated 25 years ago to be inferior to three-part. In fact, every two-part ankle that was ever commercially introduced was withdrawn from the market at the mid- to long-term point because of clinical failure.”
What to Do
If you, or one of your patients has the device, here’s what the FDA wants you to do:
If You Have a STAR Ankle
- Talk to your health care provider if you experience any new worsening pain, inability to bear weight, new grinding or other noise, or instability in your STAR Ankle.
- Be aware, your health care provider may perform a physical examination of your operated ankle and obtain X-rays to evaluate your STAR Ankle. In some instances, computed tomography (CT), a cross-sectional computer scan, may be necessary to assess if the plastic component in your ankle is broken.
- If you suspect or experience a problem with your STAR Ankle, the FDA encourages you to report the problem through the MedWatch Voluntary Reporting Form.
For Providers Who Treat and Follow Patients with a STAR Ankle
- Review the recommendations for patients who have or are considering STAR Ankle, and caregivers listed above and with your patients.
- As part of shared decision-making, discuss the benefits and risks of all relevant treatment options for painful arthritic ankle joints with your patients.
- Read and carefully follow the Instructions for Use for 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.
- Thinner (6mm) plastic components appear to be more prone to fracture.
- Younger patients (under 55 years old) and patients with a primary diagnosis of osteoarthritis may have higher risk of plastic component fracture and subsequent revision surgery.
The agency said it continues to work with Stryker to better understand what contributed 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, health care providers, orthopedic professional societies, and the manufacturer.
In addition, the agency said it will continue to work with the company “to ensure that patients and providers are aware of the potential risk of plastic component fracture, to identify any potential mitigation measures, and to ensure that the product labeling addresses the concern.”
If you have questions, email the Division of Industry and Consumer Education (DICE) at DICE@FDA.HHS.GOV or call 800-638-2041 or 301-796-7100.
