Osgood-Schlatter disease

Osgood–Schlatter disease (OSD) is inflammation of the patellar ligament at the tibial tuberosity (apophysitis). It is characterized by a painful bump just below the knee that is worse with activity and better with rest. [Source: Wikipedia ]

Osteonecrosis of the tibial tubercle
OrphaNet reference
Osgood-Schlatter disease 
Is A
Site-specific avascular necrosis
May Cause
Patella alta