In reply to Dave Mountford:
You have probably read the thread on this that I started not all that long ago. Lots of people climb perfectly ok with replacements but it seems there will always be a question mark over how much flex you will end up with in the joint (I get the impression that surgeons will be understandably cautious in their predictions).
Having seen a surgeon, I have, on his advice, been using painkillers to keep pretty active in the hills, knowing that I can get them done when they become too restrictive. I have learnt to manage them pretty well. It seems important for a good recovery to get them done while still fit and strong, not after becoming inactive for an extended period, so a tricky balance.