Approximately one in five active adolescents gets Osgood-Schlatter disease, and most of them are boys. Marcie Fraser reports.

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Osgood-Schlatter disease is more common in adolescents who participate in sports that involve swift changes of direction like soccer or basketball.

"The teenage population there is a growth plate behind the tibial tendon runners and jumpers have it more often there is a genetic component," said Dr. Jonathan Gainer, an orthopedic surgeon.

It begins during puberty when kids go through growth spurts.

"In the early teens the growth plate is wide open and the bones are growing fast and the ligaments are trying to catch up and that as when they are active in sports," said Dr. Gainer.

It's a traction injury to the growth plate.

"The growth plate is a softer cartilage model where it advances forward and leaves bone in its place so as it is pulling at the growth plate it's causing a tendon injury, it is similar to tendonitis in adults," Dr. Gainer explained.

The bump is partly made up of calcified bone.

“As the growth plate gets pulled out and gets bigger, hypertrophy and fills in bone behind it and it keeps getting bigger," said Dr. Gainer.

Symptoms include mild pain just during activities to constant excruciating pain. Kids also experience swelling and tenderness at the bony prominence just below the kneecap, a tightness of the surrounding knee muscles, and sore thigh muscles. Once you have the bump, it never goes away, but rest can prevent the it from getting bigger.

"Trying to decrease the activity until the pain decreases, stretching exercises, strengthening and mostly waiting for that growth plate to close," said Dr. Gainer.

If you child takes no breaks between sports, their risk is higher.

"They have sports that run over and cross over seasons, are in sports non-stop, and the body doesn't get a break," said Dr. Gainer.

While the bump can be unsightly, most doctors recommend not removing it.

"You run the risk of convulsing someone's tendon and making it a non-functioning leg. It is risky, you can take the size of the bump down but there is a lot of recovery and then you have a scar, then go from a bump to a scar, which do you like more or less?" asked Dr. Gainer.