Hey, I'm not really sure what it's about, but I get it above the knee sometimes too. Sometimes it will be my stomach, my foot or hand, etc. Strange.
If I had to guess, it would be about hampered detox pathways. When I went to a specialist (PT who does lymphatic drainage), she used a special thermometer to measure my temperature on different areas of my body. Your temp should be lowest at the extremeties and increase as you move inward. She would find these areas and knew how to curtail her lymphatic drainage session. She would retest afterward and it would normalize somewhat. I learned how to do some lymphatic drainage on my own, you might want to look into that. It seems to help when I have some pain.
Hope this helps...