Where's the pain and how did it come about? Related to posture issue?
Patellar-femoral pain
http://www.aafp.org/afp/2007/0115/p194.html
Tendinitis (with inflammation) & Tendinosis (with defective healed tendon tissue)
http://tt.tennis-warehouse.com/showthread.php?t=442912
There are many TW threads on knee injuries.