I have knee pain for over twenty years.  It first started when I would trip and fall on my knees while  running uphill.  I thought was a good exercise to keep me in shape.  First it was my left knee and 
now my right knee seems more the problem.  The cortizone injections in my left knee seem to work for a short time, . 2-3 months,  but my right knee doesn't seem to feel any better.