In the uk the emphasis is very much that you can’t do too much physio and that you must push yourself for full ROM, despite horrendous muscle pain
That is not the attitude all over the UK but, unfortunately, it's the attitude the team looking after you have.
I'm here to tell you that it's your knee and you are the only person who has the right to say what happens to it. Not your surgeon, not your physiotherapist, not your friends and family - just you.
While other people may advise, you also have the right to choose whether or not to accept their advice.
Saying no to therapy - am I allowed to?
CONSENT: what it means and how it can be used
The pain you get during and after PT is a warning sign. It's your knee, telling you that you are making it do more than it is ready to do. Listen to your knee. It knows what it's doing. It's not lazy or unfit - it's wounded and it needs rest and only gentle exercise, so it can start to heal from major surgery.
There's no need to rush to get ROM (Range of Motion) because it can continue to improve for a year, or even much longer, after a knee replacement. There isn't any deadline you have to meet:
Myth busting: the "window of opportunity" in TKR
Saying that you have to work hard, or else your nee will seize up for ever, is a complete myth that should have died long ago.
It's not exercising that gets you your ROM - it's time. Time to recover, time for swelling and pain to settle, and time to heal. Your knee has the potential to achieve good ROM right from the start, but it's prevented from doing so by swelling and pain. As it heals and the swelling goes down, your ROM (both flexion and extension) will naturally increase gradually, without any painful therapy.
My surgeon doesn't allow any formal PT at all for the first month after a knee replacement. He says your knee needs that time, to start on its journey of healing. For that month, we rest, ice and elevate our leg, and walk around the house. The walking is our exercise and we increase it a little each week.
After that month, we just go to PT once every 2 weeks, where we are shown a few new exercises to do at home each day.
His patients all do well and achieve good ROM, as I did, and he hasn't had to do a manipulation to help with ROM for the past 4 years. I think that speaks for itself.
I have had three knee replacements and I followed my surgeon's regime each time. I can do anything I want to with my knees - in fact, they're in better condition than I am - and I'm usually not aware that I have artificial knees.
Stop doing painful PT. All your knee needs is to be kept moving gently. Scar tissue won't form - it's not just sitting there, waiting to pounce.
Instead of doing lots of painful exercise, spend more time resting, icing and elevating your knee, to help reduce the swelling that is preventing it from bending.