Most medical devices do not enter the market through rigorous safety testing but by being deemed similar enough to something already approved—the "predicate" device—through a mechanism known as the FDA's 510(k) pathway. But similar is not a synonym for safe. While the assumption may be that substantial equivalence is a reasonable stand-in for a safety review, some devices cleared with this method are still recalled, and the FDA spends valuable time reviewing devices the same way, regardless of how risky they appear on paper.