I had trouble with what the specialist told me was osteoarthritis of the knees. However he did no testing and his diagnosis was based entirely on my description of the pain.
He told me to get used ot it, reduce the load on my knees and eat the ends of chicken bones. I started moving differently, avoided overloading my knees and started to eat a lot of geletine based products.
I still have trouble but it is immensely reduced.
Take a good look at how you walk and see if there is a reason you might be placing excessive load on the bad joints.