Condition	Characteristics
Osgood-Schlatter disease	Chronic avulsion of the unfused apophysis of the tibial tubercle causes unilateral anterior knee pain that worsens with activity and improves with rest; most common in boys after a prepubertal growth spurt
Osteochondritis dissecans	Joint pain in adolescents after activity; pain caused by osteonecrosis of the underlying articular cartilage and bone, and potentially subchondral stress fracture
Osteosarcoma	Arises in adolescents during growth spurts; most common in the distal femur; can cause chronic pain that is worse at night or with activity
Patellofemoral dysfunction	Inflammation in the articular surface of the patella causes anterior knee pain; common in young adults, particularly athletes
Sinding-Larsen-Johansson disease (jumper's knee)	Overuse traction apophysitis of the patellar tendon at the inferior pole of patella causes pain and tenderness at the patellar tendon and inferior patella; usually occurs in boys nine to 12 years of age