From MayoClinic.com

Osgood-Schlatter disease is a common causes of knee pain in adolescents. During your child's growth spurt, his or her bones grow rapidly. If your child is involved in a lot of running and jumping activities during this time, he or she is at risk of developing Osgood-Schlatter disease (tibial tuberosity apophysitis), an overuse syndrome that causes pain, swelling and tenderness just below the kneecap.

Osgood-Schlatter disease occurs more often in athletic kids than in nonathletes. It generally develops in boys ages 10 to 15 and girls ages 8 to 13 and is slightly more common in boys.

Having Osgood-Schlatter disease can be frustrating, because your child may need to limit his or her running and jumping activity level for a short time. But the condition is temporary - usually lasting 12 to 24 months - and as your child's bones finish growing, the pain should go away.

Signs and symptoms

Signs and symptoms of Osgood-Schlatter disease include:

• Pain, swelling and tenderness at the bony prominence (tibial tuberosity) on the shinbone (tibia), just below the kneecap

• Knee pain that worsens with activity, especially running and jumping, and improves with rest

• Tightness of the surrounding muscles, especially the thigh muscles (quadriceps)

The pain varies from person to person. Some have only mild pain while performing certain activities. For others, the pain is nearly constant and debilitating. Osgood-Schlatter disease usually occurs in just one knee, but sometimes it develops in both knees. The discomfort can last from weeks to months and may recur until your child has stopped growing.