What makes you think that a knee replacement will make you unable to go up stairs in to a Class A? I have a guy on my bowling team that went through a double knee replacement and still carries a 200+ average. There is also a woman in the same league and the double knee replacement has not slowed her down.
I know they make different knee replacements now out of various metals, as well as the plastic type knees, but I don't think I would make any assumptions as to your limitations until well after the surgery.