I used the cpm on knee #1 10 years ago. At about the 2 week mark, as far as I recall, the machine could no longer bend my knee. It would move my entire body instead of bending my knee. We tried tying the machine down, tying me down, nothing worked. Then in therapy it was like hitting a brick wall when trying to bend past 80 or 90 for months. It was slow going but eventually I got there. But I have to say, got there, meant A LOT of pushing by the PT. To the point of tears. But I didn’t want MUA, so that’s what we did.
It sounds to me as if your knee got very badly swollen, from all the CPM use and the PT pushing on it.
That was all totally unnecessary, as is using the CPM machine this time, too.
Don't make the same mistake again. Instead, concentrate on rest, icing and elevation, to try and decrease the swelling - and cut right back on the PT exercises.
Ice to control pain and swelling
Elevation: the do's and dont's
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 ROM is there right from the start, just waiting for all that to happen, so it can show itself.
Just doing your normal activities of daily living is enough exercise for your knee.
It's not even a month yet since you had your TKR, so stop worrying about your ROM.
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
My surgeon doesn't allow any 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.
After that month, we just go to PT once every 2 weeks, where we are shown a few new exercises to do at home.
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, because no one developed adhesions (bad scar tissue). I think that speaks for itself.