Many thanks to those of you who shared some experiences with security & walking casts.
I have the "Frakenboot" that goes up to my knee. It's actually all plastic & padding & tons of velcro, so I don't believe that it would set off the metal detector. But it's huge, you could certainly smuggle something non-metallic through within it. It's possible to hop around with it off, but not very far, and it's extremely difficult to get it off while standing up.
It looks like this one being auctioned on Ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll...category=19264
I can take it off, if I'm sitting down. So it sounds like my best bet is to go through the metal detector, and ask for a seat to sit in & take it off & allow them to send it through the x-ray.
If I have to do that, but the cast doesn't set off the metal detector, how likely am I to also get the pat-down and wanding? Is there any standard TSA procedure for dealing with casts like this?