FDA Panel: No Answers to MoM Hip Dilemma (MedPageToday)
Two days of public hearings yielded little in the way of solid information for an FDA advisory panel to use in promulgating new policy recommendations for use of metal-on-metal (MoM) hip implants.
The FDA’s Orthopaedic Surgery and Rehabilitation Devices panel, meeting Wednesday and Thursday, had been tasked with providing recommendations on how to manage patients who have received such devices and whether they should be used at all in new patients.
Where Are the Data?
Toward the end of the 2-day meeting, Scott Evans, PhD, a Harvard University biostatistician, said that, although the group had been presented with reams of data, “the issue is that it’s from observational studies and registries that are not optimally designed to answer the very, very difficult questions we’ve been trying to hassle with today.”
At another point, Raj Rao, MD, of the Medical College of Wisconsin in Milwaukee, protested that an FDA question about populations who should not receive MoM implants was “unfair” because the agency had offered no data comparing such devices with metal-on-polyethylene or other alternative designs.
The discussions, which did not include formal up-or-down votes, did produce consensus on some questions the FDA had asked:
- Despite the many limitations of metal ion testing, it is useful to perform such tests serially in patients with well-functioning MoM implants as well as those experiencing problems.
- Ion testing should be performed on serum or whole blood samples, not urine.
- There are no identifiable patient groups for whom MoM devices should be the first choice.
- Metal sensitivity testing, though also flawed, should precede implantation of MoM devices.
- Special MRI scans for evaluating hips with metal implants are generally not needed in asymptomatic patients, nor in patients in whom device failure is otherwise obvious, but should be routine for patients with symptoms that may or may not reflect impending failure.
- Labeling should include language that conveys what one panelist called the “extreme sensitivity” of MoM implants to correct positioning in their subsequent longevity.
- Patients should be informed about special risks associated with MoM devices — so-called pseudotumors adjacent to implants and elevations in metal ions in circulation, especially in those with femoral heads ≥36 mm.
- Asymptomatic patients with MoM devices should be evaluated yearly; patients with problems should be seen at least every 6 months until the need for revision becomes clear.
No Firm Recommendations
But there was less agreement on details that would allow development of an algorithm for managing patients post implant, such as the specific metal ion levels or MRI findings that should trigger concern.
In addition, many panel members said, like Evans, that they were uncomfortable with making recommendations on the basis of the current data, none of which came from prospective, randomized trials.
Committee members offered some unsolicited advice for the agency — that it leave room for clinicians and patients to choose a MoM device if they think it’s the best choice.
Panelists urged the FDA to avoid “blanket recommendations” that intrude into the doctor-patient relationship and that fail to take into account the wide variation in performance histories for different MoM devices.
Data presented at the meeting showed that some specific MoM implants had performed as well as the best among other designs. Although average failure rates for MoM devices have been significantly higher than for metal-on-ceramic and metal-on-polyethylene implants, much of the difference appeared to be driven by a few products with 5-year failure rates well in excess of 10%, and primarily when head sizes were relatively large.
Speakers and panelists also drew a clear distinction between MoM total hip replacements and resurfacings, in which the femoral head is shaved and capped with a metal ball. The latter have shown good durability, but are only indicated for a narrow range of patients.
Toolbox Inadequate
In addition to variability of results with different MoM designs, panel members heard evidence that many of the clinical tools offered for managing patients with or being considered for MoM implants are extremely unreliable.
- Ion testing methods and results are not standardized, and sample contamination is a ubiquitous problem. Also, correlations between metal ion levels and device function are far from perfect.
- The special MRI scans needed for imaging metal implants are not widely available, and interpretation is as much art as science.
- Results of skin patch tests for metal sensitivity and patient reports of metal allergy do not always translate to risk of metal reactions in deep tissue.
- Failure rates of MoM devices appear higher in women, but no other patient characteristics are known to increase the risk.
Another major unknown highlighted at the meeting is the mechanisms by which metal implants appear to foster what are called adverse local tissue reactions, or ALTRs.
These can have numerous different manifestations, including pseudotumors, collections of fluid, damage to the points of muscle attachment, and device loosening.
Shedding of metal debris appears to play a substantial role, but massive ALTRs have been seen in patients with relatively intact implants.
The question of whether MoM devices should be used in new patients may already have been answered in the marketplace.
Paul Manner, MD, representing the American Association of Orthopaedic Surgeons, told the panel that a survey conducted earlier this year in 600 members of the American Association of Hip and Knee Surgeons showed that only 1.4% were still implanting MoM devices.
“Alarmist Press”
But the more urgent question is how to manage the many patients — estimated at 500,000 to 750,000 in the U.S. — who have already received such implants. Orthopedic surgeons on the panel said they had been hearing increasingly from worried patients who had read media reports of problems.
John Skinner, an official of the British Hip Society, said that “an alarmist press” in Great Britain had raised broad fears among patients in the country, with many demanding to have their implants removed even though they had no apparent problems.
Graham Mercer of the Australian Orthopedic Association said the situation was similar in his country. He blamed “misinformation out there in the media.” Both men urged the committee and the FDA to do what they can to discourage unnecessary revision surgeries.