So your surgeon was inexperienced?
Most likely not inexperienced, but probably not as committed and emphasizing as they should have been. Sarcastic replies and being an uppity prick aren't helpful.
This question is really complex...was the surgeon an orthopedic surgeon, or did he have the surgery done under a more generalized surgeon? The rehabilitation plan will be vastly different depending upon the doctor and what he 'prescribes' for rehabilitation...
In which, OP, lies your answer. Eight weeks is probably a correct time frame, however, the quality of your life will depend on what YOU do in those eight weeks. If you go to your doctor scheduled rehab three times a week and put in the bare minimum, then it won't matter how long you take off, because you'll be hurting regardless. If you go to your doctor schedule rehab three times a week and bust your ass, DO YOUR EXERCISES AT HOME, and CONTINUE YOUR REHABILITATION PROGRAM INDEFINITELY, then after eight weeks you'll be a mean, green (brown, delivering machine.
A lot of doctors, particularly for patients >30 years old, have a very laxidasical attitude towards the rehab. Mainly because their experience has taught them that YOU won't do it. They are busy and won't waste their time and emotions investing in your recovery if you don't either.
My dad had a surgery done on his AC joint in the shoulder. This same surgeon set my broken arm the second time I broke it, he did my ankle surgery, and has genuinely been a very good doctor for me. However, my dad refuses to use him again, because he still has shoulder problems. My dad, like most older patients who don't understand their body, did NOT follow his rehabilitation. I remember seeing him take his sling off multiple times so he could do menial tasks that he could have easily asked someone else to do. The end result for my dad was that he now has two bad shoulders and won't have either of them worked on, because 'what's the point if the surgeries don't work'.
The surgeries work. It's the idiots who don't understand that the surgery is the LEAST important part about getting healthy. Doing your rehab, staying on top of your rehab, and taking care of your body is what will make you healthy again. Anybody who tells you any different is a fool and doesn't know what they are talking about.
Source: I have had spondylosis in my back since I was 13 years old. I have been meticulous about performing exercises that strengthen and stabilize my core muscles ever since. My buddy, who had the exact same problem, had to forego a professional career in our sport of choice and he can't ever even play the game again. He didn't have the dedication to rehab that I did. It's a damn shame too, because he was a hell of a player.
OP, was your partial replacement medial or lateral? (Inside or outside of the knee)
It would likely be beneficial to go to a sports medicine doctor who can analyze your running/walking technique. I know it seems like 'voodoo' science, but those guys who are trained well can tell exactly what muscles are too weak and what ones are too strong just by your posture while moving. We had one come out to a training session while I was in college and, even though I already knew and was working on my specific ones, he still pegged me down exactly as quad-dominant/hamstring weak just from watching me jog a couple of laps and do some 15 yard sprints.
One thing I can tell you to start working on already is learning to tighten up your butt/abs. This video covers pretty well the feeling of what 'tightening' your abs is...
. You don't need to be a skinny person to have a strong/tight core either. NFL linemen have the strongest core muscles in sports.