DEAR READER: Osgood-Schlatter (OS) causes a painful lump below the kneecap (where the tendon attaches to the shinbone) in some children. It results from growth spurts during puberty and typically occurs in children who participate in sports that involve jumping, running and swift changes in direction.

OS was more common in boys in the past, but as more girls become active in sports, this gap is narrowing. It affects about one in five adolescent athletes. Because puberty occurs at different ages between genders, OS commonly affects girls around age 11 or 12 and boys around age 13 or 14.

Symptoms of OS include tightness of the muscles around the knee, especially the thigh muscles; pain, swelling and/or tenderness of the uppermost portion of the shinbone, just below the kneecap; and knee pain that worsens with activity and improves with rest.

The cause of OS is repeated stress. Children have growth plates at the ends of bones, which are made of cartilage. These growth plates are not as strong as bone, and recurrent stress can cause injury. When the tendon that holds the kneecap in place is pulled constantly, it can begin to separate from the bone. In some cases, the body may try to bridge the gap by building more bone, causing a tender lump.

Osgood-Schlatter typically improves without treatment and disappears once the bones stop growing. In the meantime, if the swelling and pain become truly bothersome, over-the-counter anti-inflammatory medications or pain relievers may be used. Rest is also important to prevent further injury. In some cases, this may include wrapping the knee or discontinuing or reducing the offending activity. In some instances, physical therapy or strengthening exercises may be beneficial.

Home treatments include stretching, ice, rest and even switching to different activities that don’t involve running or jumping until symptoms resolve.