I had 25-30 fracture blisters of varying sizes after my first TKR in 2019. My home health nurse and surgeon said they're caused by extreme inflammation/swelling and tend to form where the skin is thinner----usually from traumatic bone breaks and less commonly after joint replacement surgery. It's a definite warning/sign not to overdo things, as your body is already dealing with higher-than-normal swelling. While Preparing for my recent TKR #2, due to my psoriatic arthritis and tendency to swell horribly, my surgeon and I made a plan for what happened if I had these again. My home health nurse in 2019 had only seen them 2-3 other times. I counted my blessings--Only 1 this time!! My swelling was initially well-controlled until Day 7-8 post-op when something else created a problem. Some of yours will probably open up. My surgeon wanted to know if they popped ASAP because of infection risk. Mostly they just wanted to give me the run-through of keeping them covered, etc.
You mentioned the pillow under your ankle, keeping your leg straight. It's advice I threw out 10+ years ago. It seems to be the #1 piece of advice everyone gets from the hospital/nurses though, with fears of never having a straight-leg again, etc. I found 3 areas in my pre-surgery packet and post-surgical packet where it was mentioned time and again, with photos of how they wanted you positioned.
This is (by far!!) the post-op advice that sets me off every time.

I've had 11 knee surgeries before this recent TKR, 5 of which had lonnnng recoveries. I NEVER had trouble getting my extension back, in fact it came back fairly fast each time---even though I swell horribly (for months!!) and get loads of rebound swelling from exercise (for months!). I use what pillows I want. Since my last TKR though, I definitely swear by the Lounge Dr. I've had friends see it and warn me of what all the nurses say ((AGAIN!!)), and I just nod and smile, ignoring every word.
Funny enough, my mother-in-law asked me ((genuinely)) why I get so mad about this "no pillows, prop your ankle" advice, as a family friend just had TKR a week before me. He was following it to the letter of the law, and was miserable with his leg propped straight ALL NIGHT LONG---getting little to no sleep.

I asked her if she would try a simple experiment, as it would mean more than any explanation. I told her to sit on the floor, prop her ankle on a rolled towel about 2 inches off the floor, and stay that way for 45 minutes (long enough to get the idea of being uncomfortable!!). She went home and did it, said she made it to the 25-30 minute mark, thought about quitting, made it to the 40 min mark, then quit!! She was so stiff it took awhile to walk normally, and as a perfectly healthy, mobile 75 year old woman,
she was extremely uncomfortable. She asked how anyone could do that all night long or all day long??? My words were
"EXACTLY!!!! Now do it all day/night with a leg that had been cut open and put back together, .every night for weeks, when you're having bad pain from the surgery itself!!!
She called it "barbaric" torture! Then I told her to go a step further and imagine a physical therapist pressing on it like that for minutes at a time, days after surgery, as a form of "helpful therapy". She said it's no wonder I've lost my trust for physical therapy and patient care. She agreed everyone should have to experience these things before handing out advice. She was glad I threw out the advice that just gave me more pain to deal with and simply let my body guide me.
I'm off of my PT/torture soapbox now.
