A recent study looks at what kind of implants will lead to possible travel delays in the airport:

As part of the study, 129 patients with 149 various implants walked through an “M-scope three-zone” metal detector — a common type at airports — at high and low sensitivity ratings.

Half of the patients — 52 percent — sailed through without the implants being detected. They usually had small nails, plates, or screws, or they had implants in the upper half of their body, the study said. “It really surprised me that only half were detected,” said Rodriguez, who believed that small implants and those encased by bone attributed to the misses.

Those with new hips or knees, though, need to plan for some extra time at the gate. All of the hip replacements and 90 percent of the total knee replacements were detected at the low-sensitivity settings. And cobalt-chromium and titanium implants were more likely to be detected than stainless-steel implants.