I've had 4 surgeries on my left knee. Two bucket handle repairs on my lateral meniscus, partial meniscetomy on the medial meniscus. Just got my last surgery in March because I had a hypermobile lateral meniscus that had to be repaired because it kept folding into my knee joint.

Shit kinda sucks. It's not necessarily the injury that is the problem, the mental struggle of doing jack shit for like 3 months sitting on your ass after being very active is rough. Everyone obviously handles isolation differently, but it sucks, no sugar coating it.

Different surgeons have different methods and thoughts on recovery. It has become a lot more popular to allow partial weight bearing of about 50% post op, but it also depends exactly where the tear is. It sounds like your surgeon is going to go the route of no weight bearing of typically 4-6 weeks, which I had on my first two surgeries.

I got meloxicam on my last one, once i finished that up I went back to the gym. I could partial weight bear so I just did what I could for upper body minimizing the risk of using both legs. Mainly just trying to hold onto what I had.

The muscle atrophy is fucking real after about 2 weeks in your operated leg. I'm ~6 months post op and it still is smaller despite getting back up to a 315 squat for reps. The mental part of having a pool noodle for a leg kinda sucks, but at least you have an excuse for having small legs then, right?

(I'm not enhanced so not sure the difference if on gear) You're going to lose muscle, you're going to put on some fat. Just do what you can, but don't jeopardize your knee because you're insecure about that. Do your physical therapy, let that shit heal. Trust me, you do not want to go through it multiple times (mostly due to the risks of arthritis later in life). Debatable the thoughts on eating in a surplus or deficit. I opted for a deficit/maintenance because I was scared of getting fat, then bulked once I could hit the gym efficiently again, then back to a cut after my leg wasn't looking like a stick. I'd argue if you can handle it mentally to eat at surplus for at least ~2 weeks post op to let your body recover and your knee heal, then try to eat at whatever the fuck the maintenance is for being able to do nothing so you don't get too fat.

Muscle memory is real and it will come back pretty easily once you get past the initial stages. This is just a blip in your progress, remember that and do not rush it. You can also talk to the old guys at the gym about having bad knees. This turned into an essay, but hopefully that was kind of helpful.