What can be done for a teenage athlete with knee joint pain everytime after sports?

Depends on the cause: Many teenagers experience pain with activities from softening of the cartilage of the kneecap or from growth plate traction (osgood-schlatter disease). These tend to be a mild ache and resolve with cessation of activity and ibuprofen. If the pain persists after the activity, is not relieved with ibuprofen, occurs at night, or is associated with swelling, see your orthopaedic surgeon.