I could end up in a wheelchair for a few months due to surgery on my knee soon and was wondering if it's possible to get a disabled badge for a short time (ie temporary while I am unable to walk)?
it is possible but in my experience VERY difficult... depends on the council you have to deal with I think. I gave up in the end - 3 months on crutches with other people driving was easier!
The only thing is to apply for one as you may need it for more than 3 months. The number of people I see using them that don't seem to have a problem walking amaze me. Apply for one, see the doctor and you can always send it back when you no longer need it.
I tried to get one of these recently for similar reasons. You need surgeons letter and a minimum of 8 weeks to process the application (Bucks). IN other words no. Unless you can somehow do it in advance which it had never occured to me to do
Maybe I should try and become a "career cripple" like half of the disabled badge users I see 
Not 100% sure of what's happening yet but I think I'm having ligaments re-attached, they're probing me more on thursday for further info