When your leg moves, the thigh muscle pulls the kneecap. Next, the kneecap pulls a tough band of connective tissue. This tissue then pulls on a bony lump at the top of your shinbone. In some kids, all that pulling can cause Osgood-Schlatter disease. This causes pain and often swelling on the front of the knee. The symptoms may limit your activities. This is because the pulling happens in an area of the bone that’s still growing. As a rule, growing parts of a bone are weaker than other parts. This makes the growing area more likely to get injured.