Wow! 25 years ago and still squatting 500! That's nice to hear! I had a bilateral partial knee replacement to the medial cartilage. I did competitive judo and jujitsu for over 25 years and it took it's toll on me! I also used to do power lifting which did not help! I've been kind of hesitant lifting heavy and completely omitted Judo and such due to the impact and injury potential. Hearing of your squat's, I am plan on lifting a bit heavier, been doing all body weight stuff the past 3 years due to the PKR. I'm in my 50's and need to keep healthy for 10 more before retirement as a fireman. As my experience for the bilateral partial knee replacement (PKR), everything is fine, but I did loose a ton of flexibility. I need to work on both strength and flexibility, but no pain since the surgery. Good luck!