Hello @izfrankd, Thank you for the private message. I thought I would answer it in the same discussion where you posted your question after your first post.

I don't believe they cut into the muscle but I'm not sure. Here is the step by step procedure for doing a knee replacement for more information - Knee Replacement Surgery Procedure: https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/knee-replacement-surgery-procedure

Your first post was about the knee buckling and you mentioned going back to your doctor who ordered more physical therapy but that hasn't helped and you still have pain and swelling. Here is an article you might find helpful -- The unstable knee: wobble and buckle: https://pubmed.ncbi.nlm.nih.gov/25381421/

Have you thought about getting a second opinion