Hi Whatawizard, sorry to hear you have to have an op.
My 80 year old aunt has just had both knee caps replaced, about 2 wks ago, as you can imagine she is struggling.
Most of the ladies who had one knee cap done, were up and about and walking around the ward with a stick, but she had to struggle with a frame. So hopefully if what she has said is anything to go by you should be gadding about before you know it.
Good luck with yours beejay.