I feel your pain!!! I just had to get a cortisone injection in my left knee yesterday! OUCH! But, good for you for doing your lower body...strength around the knees really does help...I so a lot of squats but never really deep ones to save my knees. Quads and hamstrings are very important for knee stabilization...I will be urging you on...keep going!
Yeah I've always tried for balanced development. Try to develop opposing muscle groups as evenly as possible. Plus it looks better too! ?
What caused this?
Mostly bad genetics. Lots of arthritis and bad joints on both sides of my family. Plus I started lifting when we really didn't know much about the best way to do that.