Osgood-Schlatter is a complaint we often see in young boys who are growing up and are fanatically involved in sports. During fanatical sports, the tendon of the rectus femoris (upper leg muscle) is often pulled hard. These pulls cause irritation at the attachment of the tendon to the bone, which can be noticed as a hard lump on the shinbone. Osgood-Schlatter's often cause pain in the knee. A recognizable symptom is pain during sports, which sometimes gets worse. It is important in Osgood-Schlatter's case to keep moving but, for example, to play sports less intensively.