USA – The Best Predicate or the Worst?

Selecting predicate devices for a 510(k).

FDA’s 510(k) process requires the comparison of a candidate device to a similar device that is already legally marketable. The objective of this comparison is to show that the proposed device is at least as safe and effective as the already cleared device. This assumes that the predicate is itself safe and effective. Predicate comparison is generally done without a clinical trial, a situation that sometimes generates heated controversy, especially after a device proves to be problematic.

In a crowded field the question arises of which of several already cleared devices one should choose for comparison. If we believe in constant progress, then the answer should be that the comparison should be made to the best currently available device, however best might be defined. For some attributes, there might be a relatively straightforward parameter that reflects a best performance. For example, fatigue resistance might be a critical parameter that can be measured and compared, assuming in vitro results reflect actual in vivo performance. If there were several devices on the market, they could be studied and ranked in order with respect to their relative fatigue resistance. It would then be nice if a new design were shown to be at least as good as the best. But what if the new device isn’t that good, but it is better than the worst? You could then choose the worst as your predicate or any other that your device is better than.

It might be the case that the worst available device is in fact good enough with respect to real-world performance. In the fatigue example, this would be the case if the worst device did not exhibit actual fatigue failures. This could be the case if the fatigue testing is not predictive of actual use conditions. But then why are we measuring a parameter that doesn’t actually matter? On the other hand, if devices pass the test and undergo field failures anyway, then the test is not helpful…