In reply to Marmoset:
Have they given you an estimate for how long you'll be out of action?
I did my first (tentative) hill walk 2 weeks after my op, and was winter climbing 3 weeks after that.
I never had much upper body strength to lose, but my leg strength didn't really suffer. Just make sure you ditch the crutches as soon as the surgeon says you can (I was lucky and never needed any).