The second day of the U.S. FDA’s orthopedic devices advisory panel included a proposal to down-classify semi-constrained toe joint prostheses as class II devices, but the panel was adamant that such devices be slotted in class III, with one panelist referring to the literature for these devices as “garbage.”
The Sept. 9 session of the two-day FDA advisory commenced with a review of the case for class II designation of cemented total first metatarsophalangeal (MTP) replacement devices, the scope of which was limited to devices that require fixation with cement. The scope of the proposal was limited to devices regulated under product code LZJ.
Michael Owens, assistant director of the division of hip and shoulder devices at the FDA’s Center for Devices and Radiological Health, said many of these devices were cleared in the early 1990s, before cross-linked polyethylene was available as a material. The product category was created by a pre-Amendments device, although the agency has cleared more than a dozen such devices over time.
These devices are broadly indicated to address painful and/or severely disabled great toe joints, such as is caused by hallux rigidus. Another example of a device for this general condition is the Synthetic Cartilage Implant (SCI) device by Cartiva Inc., of Alpharetta, Ga. Cartiva won a PMA for this device in 2016 after an appearance at an FDA advisory panel, although the agency had indicated at the time that it may require five years of follow-up for those enrolled in the pivotal study. The SCI is regulated under a different procode (PNW) however, although the SCI’s track record came up during the Sept. 9 hearing’s proceedings.
Owens said the FDA literature search captured eight articles in the peer-reviewed literature, which included summary data on the primary use of the first MTP implants. All but one of these entries were level IV case series reports, and Owens noted that effectiveness for relief of pain for restoration of motion “had mixed results.” Revision rates were conspicuous in the literature, but the devices are associated with significant bone loss at the implant site, which he said, “places patients at risk for multiple secondary surgeries.”
Device may never integrate into native bone
Perhaps the most outspoken opponent of class II designation was Glenn Pfeffer of Cedars-Sinai Medical Center in Los Angeles, who said “these types of implants never get a chance to wear.” Pfeffer said the devices loosen over time and may fracture the bone, adding that in some instances, the device never incorporates into the foot.
Pfeffer said that any comparison of materials with the materials used in hip and knee implants fails to account for the fact that the hip and the knee are surrounded by muscle mass and connective tissue. The pressure on the toe is not offset by surrounding mass to compensate for stress, a picture he said that is “very different from the total knee.” Pfeffer alleged that device failures, when reported by patients, are not reported to the FDA as an adverse event.
Pfeffer said the body of data on outcomes would suggest the patient is not receiving adequate informed consent about the hazards associated with these devices, adding that the salvage procedure for a failed Cartiva device requires device removal and infilling of the inserted bone mass. “Large amounts of bone have to be removed” in order to implant the device, and thus the patient is left with a large defect if the implant fails. The remedy may require harvesting of bone from the iliac crest, but either way, a failure of these devices is “a horrible, life-altering event for the patient.”
“It may be a moot point. I don’t think anyone wants to put these things in anymore,” Pfeffer said. The gold standard is still fusion of the great toe, but he acknowledged that there are few particularly attractive options for anyone who still has an active lifestyle. Still, these other options may be preferable to “an operation that could literally destroy the rest of their life.” The reason a PMA is critical for these devices is that “the literature on this is garbage,” Pfeffer said. The discussion of class II designation for MTP devices ultimately fell apart due to a paucity of data on which to base a class II recommendation.
Pressure monitors backed for class II designation
The second day of the advisory hearing dealt with two more device types for which a class II designation was examined, including intracompartmental pressure monitors, which are currently unclassified. The FDA’s Peter Allen said the proposal for class II designation is limited to devices regulated under procode LXC, which are currently run through the 510(k) program. There are nine total cleared devices in this group, for which clearance dates range from 1985 to 2020. A literature review yielded eight sources which indicated that these monitors are the most reliable adjuncts to diagnosis of compartment syndrome.
One study yielded a 94% sensitivity for acute compartment syndrome and 98% specificity. The proposed regulation would fall under Part 888.1700 of Title 21 of the Code of Federal Regulations, and would call for evaluations of biocompatibility, and for software verification, validation and hazard analysis. Allen said the proposal also calls evaluation of all electrical components and validated reprocessing instructions.
Some of the panelists argued that the associated tissue risk is exaggerated, including the purported risk of shock or electrical burn to the patient and the purported electromagnetic interference with other devices. User error was a potential issue that gained some traction among the panelists, something that could be addressed by including a thorough description of the use of such devices in product labels’ instructions for use.
The special controls were generally seen as adequate with the addition of labeling to address the potential for user error. This includes an assessment of mechanical specifications to validate the accuracy of the probe’s pressure measurement, although there was some support for a class I designation.
Intra-abdominal pressure monitors under procode PHU were also seen as appropriate for class II designation with special controls, a move that was unanimously backed by the panel apart from one abstention. As was the case with intracompartmental monitors, one panelist suggested that class I might be appropriate.
At present, there are only two devices in the 510(k) database with the PHU procode, one from 2007 and the other cleared in 2016. Among the risks to be evaluated are adverse tissue reaction, infection, local tissue injury, incorrect diagnosis and user error. Unlike the previous device, there was no study for PHU devices that recited a conspicuous rate of user error.