As long as leg presses and hamstring curls don't hurt your knee, I'd add those in with a ton of biking/elliptical, etc. If that hurts, maybe just a bunch of straight leg raises (sit on the floor, straighten leg, lift maybe a foot off the ground, repeat to infinity). The more muscle you have before surgery the better. Without PT supervision, I'd just do gentle quad and hamstring stretches (whatever you can do without pain - I wouldn't push into anything that feels painful at all without supervision). As in touch your toes and pull your foot in towards your butt. If you don't have much flexibility, start with wall slides - lay on your back, legs up on the wall, and wear a sock so your heel slides down towards your butt. It's also a good one becuase you can try to relax and let gravity do the work.
"Life should not be a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "Wow, what a Ride!"
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