Stiffness after knee replacement: Is it a reduction in blood flow?

I have been in PT 3x, had a CT and it showed a mild effusion on the knee they are not concerned about. No mechanical issues with the hardware or fractures. However I did have vascular calcification around my knee and they are sending me to vascular to see if there is an issue with blood flow. My knee is still so sore and stiff no matter how much I do. I walk a lot, range of motion is 125 and do all I did before surgery however nothing helps the soreness and stiffness and the longer I go through my day the worse it gets. If I sit too long it's difficult for me to just start walking and I have to wait a bit as well as well as when I get out of bed. Did anyone find that lack of blood flow caused issues with their knee after a replacement? I'm hoping this is the answer to why it hurts. Heat helps tremendously and I know that heat increases blood flow. Thanks for any information and experience you may have had.