I've had a couple of arthroscopies on my right knee and it was a couple months before I could do much in the garden. A friend had his left knee replaced and was unable to do much at all in the garden for around six months. Your big problem will be digging and kneeling, your best bet is to actually ask your physio.

You're being a bit optimistic, but no harm in that!
If you can't get anyone else to put them in for you perhaps you could dig trenches rather than individual stations before the op, and afterwards just drop the tatties in and rake the soil back, if you're up to it, or, more likely get someone else to rake it for you? You'd probably have to forfeit earthing up. Hope the op goes well anyway, and you have a straightforward recovery.

My Mum had re-placement knee's and was told not to kneel any more?

Kneeling isn't easy after a knee replacement but our friend can kneel just not for long and it isn't comfortable. e tends to sit on his bottom and shuffle, but that is no help for planting potatoes!