I've been told that if you don't bust your butt and let the pt bend and twist your knee that you'll develop lots of scar tissue and won't be able to bend or straighten knee at all. Then your os will have to re-open the knee to clean it all up. How true is that
It's not true at all. It's a total myth.
Bad scar tissue (adhesions) is actually quite rare, in spite of what the therapists say. It isn't just waiting to pounce if you don't exercise enough.
In fact, doing too much exercise, over-working your knee and making it hurt will cause your tissues to get angry, hot and inflamed. Hot tissues are often more dry than normal tissues and that dryness can increase the likelihood of getting bad scar tissue. There is no need at all for your therapist to even touch your knee.
It sounds to me as if your PT therapist is trying to frighten you into working harder, with the threat of more surgery if you don't. Try not to listen, because she/he is wrong. I think it's unprofessional and thoroughly wrong to try to frighten people into working harder.
There is absolutely no need to rush to get ROM (range of motion), no deadline by which you must achieve it, or all is lost. ROM can continue to improve for a year, or even longer, after a TKR.
Myth busting: the "window of opportunity" in TKR
What a lot of PT therapists do not seem to realise is that it isn't exercise that brings back your ROM. It's time and the reduction of swelling. The ROM is already there inside your knee, just waiting until it can show itself.
and how does having hypertension knees affect having a tkr?
I'm sorry, but don't understand your question. Can you state it a bit more clearly, please? Do you have hypertension, or is that meant to be another word for something to do with your knees?