Yes it does exist in North America, as I've seen them being used by Ian Millar, here in Canada and in some tack shops. And I rode with such a couple of time but they were from the co. GPG http://www.gpgstirrups.com/stirrups-c-45.html
I personnally found them pretty big and heavy and since I don't have any back/knee problem, I prefer my KAt 'n JIn large foot bed stirrups better!
But I still had found them comfortable and had more real suspension than the 'regular' 4way stretch rubber sided ones.
GPG seems to now have a device you can use with your own iron! Might see if I can try that!
I know a number of people who ride in stirrups like that and have ridden in them myself, but I wasn't a big fan. It feels very weird at first, though I'm sure it's something to get used to. I tend to overflex my heels and ended up feeling like I was going to lose my stirrups all the time. Apparently makes a big difference over the GP height fences (on the landing side) but I am just picturing the stirrups breaking mid-course at some big event! I've seen a lot of stirrups break mid-ride.. And I'm talking expensive ones like the Royal Riders! But guess that will come into play with any piece of equipment that is heavily used and has moving parts.
I'd rather be riding!
Me too! I can't decide if this makes sense to me. I am thinking the biggest benefit for a back problem would be for landing from a jump?
I don't know how much sense it makes either, but I'm open to trying. It will be a while before I'm back in the saddle, but I do fear the long term ramifications of my injury (fractured T6 & T8 vertebrae) will affect my riding.
On the bright side, pretty darn grateful I will be able to ride...so will figure out the rest as it happens.