I am 14 and i have the same problem but mine has gotten a lot worse. Durning track and feild at my school i was in the high jump and on the 3rd jump i completely tore the petelar tendon right off the knee cap. The best thing to do for Osgood Slaughters disease is to work a lot on building thigh muscle. When thigh muscle is strong it takes strain off the tendon and it has to do less work. Also calf exercises are good for helping keep the disease at a minimum harm.