Osgood-Schlatter disease is thought to be caused by small injuries to the knee area from overuse before the knee is finished growing.
The quadriceps muscle is a large, strong muscle on the front part of the upper leg. When this muscle squeezes (contracts), it straightens the knee. The quadriceps muscle is an important muscle for running, jumping, and climbing.
When the quadriceps muscle is used a lot in sports activities during a child's growth spurt, this area becomes irritated or swollen and causes pain.
It is common in adolescents who play soccer, basketball, and volleyball, and who participate in gymnastics. Osgood-Schlatter disease affects more boys than girls.