Yen- This IS the 50+ forum, so I think a lot of it goes with the territory
Some of it may be that you are favoring the knee(s), so you walk a bit different and put the "strain" elsewhere.
Some years ago, I had my wrist in a cast, and after a few weeks, the OTHER wrist started hurting. The Dr. explained it quite simply- It's because you're USING the other wrist MORE!
BTW, I (and my "little" brother who is also 50+) have found that taking a Calcium, Magnesium & ZInc tablet every day, really seems to help joint pain. It's quite inexpensive. You might try them and see if that helps after a couple weeks. I have a couple waitress friends that have tried it and it helped their wrist pain.