Hi,
this condition particularly occurs in teenage boys and is because of overuse of Quards in atheletes. hence rest and ice in the initial stage will be helpful. then you can start with isometric exercises for quards and progress to isokinetic exercises as the pain decreases.
you can advice the patient to avoid extreme knee flexion and sports.
if this also doesnt help then you can prescribe a knee brace.
the condition takes 3-4 months to improve.