K.L.
Hi Angela,
I am an Orthopedic Physician Assistant and OS is something very common we see in adolescent athletes. The issue is the growth plate on the front of his shin bone becomes inflammed from the impact from sports. A tendon that attaches the kneecap to the shin bone is also in this area. He will continue to have this pain on & off until he finishes growing and his growth plate closes. When he does have pain, its important for him to REST. Ice & antiinflammatories are also key (advil, aleve, motrin..whichever works best for him). The more he tried to push through the pain, the worse it will get.
Also FYI, it often affects both knees, although not at the same time. So if its only in one knee now, it may become an issue at some point in the other knee down the road. Again, the good news is that this will not be an issue once he stops growing!
Good luck!