Having rheumatoid arthritis has sadly stopped me from caving, but I had a total right knee replacement about three years ago, and I really cannot imagine it interfering with caving, as long as a bit of sensible care's taken. If I kneel on a hard surface it's pretty uncomfortable, but using knee pads means I can kneel without problems.
As Mrodoc mentions, doing the exercises those nasty physios give you is vital, both before and after the operation, if you are going to rehabilitate quickly. A friend had a knee repacement at Hexham hospital last month, and was out of hospital the following day. He was playing bowls within a week, and has just left to go to Northern Ireland to play bowls for the English police team.