I don't know if this will help you all, but after my initial meniscus surgery as well as my replacements, the back of my knee was sooo tight, it hurt to touch it. A massage therapist convinced me to let her massage gently, and I worked up from there. I started using a vibrating massager (not a percussion / gun massager) on the back and it got so much better. I would place it under my leg while laying on the bed. It eased up those tension a lot.
(Smile), I had to replace my massager and in searching online, all that came up were the gun type. I had to search for "vibrating massager". While I found one, it was quite entertaining and a bit scary! 🙂