Jumper's knee? I went in to have my knee checked out because I was in a lot of pain and thought I had torn something. The doc basically told me I had weekend warrior syndrome. When I lived in Vail I skied almost everyday. When I moved to Denver, I could only ski on the weekends. I was heading up every Wednesday afternoon to put on this jumping show that took place on Wednesday nights.
Long story short. He had his PT put me on a table and made me do a stretch that just about made me pass out. There is a muscle that is like a leather belt strap that runs from your butt, around the outside of your quad and connects to your kneecap. In cases like mine, the muscle had gotten stiff and contracted and was actually pulling my knee cap out of alignment so that when I flexed or extended, bone was rubbing on bone.
For the stretch he had me lay on my back and hold my right leg up at a 90 to my body. Then he pinned my right shoulder and pushed my right leg across my body as far as he could. You can do the same stretch in a few different ways. He suggested throwing a towel or belt over your foot and pulling it over.
Bottom line is that if you do this stretch and it hurts like sin, you can blaim that muscle band for at least part of the problem. Hope that helps.