FDA panel seeks to answer agency's questions about MoM hip systems
After a 2-day meeting, the Orthopaedic and Rehabilitation Devices Panel of the FDA’s Medical Devices Advisory Committee found that the data on metal-on-metal hip arthroplasty systems was plentiful, but insufficient for the purpose of definitively recommending or condemning the use of these devices.
With widespread use of metal-on-metal (MoM) devices, the FDA noted in an introductory statement that more information is available on these implants, including clinical performance and adverse events. Some of this data has revealed safety concerns, such as local complications, early device failure and metal ion exposure — concerns the FDA cited as warranting open, transparent dialogue among researchers, device manufacturers, physicians, the public and the FDA.
The mission of the panel, led by William Rohr, MD, was not to vote on what — if any — actions should be taken with regard to MoM devices, but rather to gather information on these systems. The FDA’s goals for the meeting included a review of currently available data, generation of scientifically based recommendations for clinical and patient communities on how to best communicate and mitigate risks, and the creation of recommendations for symptomatic and asymptomatic patient follow-up.
“We are here primarily in a listening mode,” Rohr said during the panel meeting.
Importance of metal ion levels
Metal ion levels and level testing were a significant part of the proceedings, as the panel heard testimony from numerous physicians, researchers and industry representatives.
In his presentation, Bernard N. Stulberg, MD, said metal ion level measurement can be used as clinical tool to help monitor patients who have undergone MoM total hip arthroplasty (THA) or hip resurfacing with symptoms and concerns of failure. As a research tool, it can monitor effects on patient populations over time to confirm the presence or absence of adverse effects. Critical to this usefulness, however, is consistency.
“Ion testing is an adjunct in addition to history and physical examination, as well as imaging of some type,” panel member Stuart B. Goodman, MD, PhD, said. “What are more important than one absolute value are multiple values sequentially done over some time period by the same laboratory according to the same methodology.”
The use of metal ion level testing as part of a protocol designed to detect which implants may be particularly susceptible to failure was discussed, and the panel came to a near, if not full, consensus on the idea that metal ion levels were an important tool. The panel did not arrive at a consensus as to what levels would promote concern or whether baseline metal ion level testing was a necessity.
Panel member Edward Cheng, MD, described his stance as “a bit more on the aggressive side” and said he believes baseline studies should be performed.
“Over time, it may change the management of the patient,” he said. “I would do metal ions and the baseline MR, because if you are going to show any change over time, you are going to need the baseline study.”
He added, “I say this with a little bit of caution because I have concerns that patients might erroneously act on abnormal test results with no real reason to do so.”
Industry representatives presented their respective companies’ findings with regard to MoM hip arthroplasty and resurfacing.
“No single bearing surface meets the needs of all patients,” Paul Voorhorst, MS, MBA, DePuy Orthopaedics’s director of worldwide biostatistics and data management, said. “Not all metal-on-metal products are the same, and each should be evaluated on its own merits.”
Voorhorst’s sentiments were shared by other industry representatives, who stressed action should be taken on a device-by-device basis rather than on MoM systems as a whole.
Rohr asked the industry representatives for their opinions as to why, given improvements in polyethylene materials and technology, MoM implants should continue to be used.
“The obvious reason is the resurfacing system allows a young, active patient to have greater activity,” Tim Band, MBA, Global Director, Advanced Bearing Systems, ASD, Smith & Nephew, said in response. “Mortality rates are lower overall in the 7-year postoperative period. The fundamental improvement, of course, is that it preserves bone stock.”
Panel member Scott Evans, PhD, agreed with the notion that the apparent heterogeneity between some devices does warrant a closer look, but noted that the higher revision rates of MoM hip implants cannot be ignored.
“We are seeing higher revision rates with [MoM] when compared to alternatives, especially in women,” Evans said. “There is some evidence of some heterogeneity of the various devices and that merits some evaluation … we have seen how these devices work under elite surgeons in ideal situations, but not all surgeons are elite and not all situations are ideal.”
One of the questions the FDA asked of the panel was to find a consensus on how, in light of the evidence they heard during the 2-day meeting, they would treat a patient with a symptomatic MoM hip. The general consensus, as summarized by Rohr, was that every patient should receive a history and physical examination as performed by the orthopedic surgeon, followed by general X-rays. Abnormalities in the X-rays, he continued, should result in the patient undergoing further imaging tests.
The panel listed risk factors that would lead them to perform further testing. These included implant head size, a female patient and bilateral implants.
Although the panel did not reach a consensus on the necessity of baseline metal ion level testing, Rohr did note in his summary that the panel supported the use of such testing if the patient had gone through other workups and the physician was still unsure as to the presence of a failed implant.
Regarding labeling, the panel consensus was that the FDA should explore additional considerations concerning the technical difficulty of implantation as well as a warning to patients that pseudotumors and elevated metal ion levels have been reported in symptomatic and asymptomatic cases. The panel also determined information needs to be disseminated to patients in a more accessible fashion — as patients need to be informed of the risks inherent to MoM treatment.
Rohr stated his final stance regarding MoM hip implants, which was that he does not use them and did not see any convincing evidence to do so. Other panelists had more mixed feelings on the subject, noting that while there is much to be understood about the implants, there were also potential benefits to using the devices.
Panel member Adolph J. Yates Jr., MD, noted that while the data showed long-term success for some patients and implants was possible, the same controversy does not exist with the option of crosslinked polyethylene.
“At this point in time, I cannot think of any indication where I would not feel more comfortable using metal-on-crosslinked polyethylene as my first choice,” he said.
Panel member Stephen Lyman, PhD, noted, “There are a lot of therapies that are potentially toxic to the patient, but we stop using those when a safer treatment comes along. I have seen no evidence that safer treatments we have are less effective.”
He added, “The question I am stuck with is: There are functional benefits, but at what cost? How much functional improvement is worth doubling our revision rate at 10 years?”
Several panel members said that while there was an abundance of strong background information presented at the meeting, there were some areas that lacked information — such as specificity.
“It does not seem to me that we have come anywhere near an explanation that actually defines everything we see,” panel member Stephen Li, PhD, of Medical Device Testing & Innovations LLC, said. “This is not to say the information is not valuable — it is just we have so little specificity, we never seem to be able to explain the whole phenomenon.”
Although the panel praised the amount of information presented and was able to provide answers to the questions posed by the FDA, the meeting ended with a number of other questions unanswered. The need for more information is immediate, some in the panel noted, as the implants have already been in use for some time.
“The horse is out of the barn,” Yates said. “We are not going to be able to go back. These devices are in hundreds of thousands of patients.” – by Robert Press and Kristine Houck, MA, ELS