After suffering from severe knee pain and rather than opting for surgery, I started doing some serious research (I mean Googling!). One of the things I realized was that my shoes had little support (I mostly wore Sketchers because they were easy to slip on and off).
Once I tried Brooks shoes there was a dramatic change. One thing about Brooks is that you can take an online survey and they will recommend which shoes are best for you depending upon supination or overpronation. Rather than flat flip flops for the summer, I wear Fit Flop sandals which have more support. Definitely don't go barefoot, even at home, if you have knee problems.
Along with reducing sugar and other food recommendations by the Arthritis Society, and taking a water aerobics class, my knee pain is no longer an issue.
Note: Brooks shoes are not cheap but well worth the cost. You could also opt to go to an athletic store such as Runners World and they will measure and fit shoes specifically for you.