What difference does the card make? My friend has a hip implant and he received a similiar card from his doctor.
When he goes through the metal detector, of course the implant triggers it, so he has to do the pat down / wanding. No big deal, by now he is used to it.
In the beginning he showd the card, now he doesn't bother anymore. I didn't notice any difference in the checking procedure, wheter he showed the card or not.
That being said, last time we flew out of Orlando, we got to use the Full Body Scanners (aka Nude scanners)

and it made a huge difference, no tap down / wanding this time, got through security much faster.