OSD

Osgood-Schlatter disease (OSD) is one of the most common causes of knee pain in the adolescent. In the US, exact incidence is not known, but it is quite common.
Consisting of pain and edema of the tibial tubercle (and hence this is an extra-articular disease), OS disease is generally a benign, self-limited knee condition associated with 'traction apophysitis' in adolescent boys and girls.