Shame the knee op will put you out of action for a few months now I'll tell you about the hip the first one took 4 weeks before I was up and around and 3 years off detecting before I got back into it that's the first one,the second ( same side ) was a reconstruction that has taken me 4 months to get back on my feet and I don't know when I'll be detecting again

.
good luck old mate I hope you heal as fast as your one liners.
regards Harry