What condition is associated with pain and swelling below the knee, particularly in adolescents?

Osgood-Schlatter disease is a condition that commonly affects adolescents, especially those who are active in sports. It is characterized by pain and swelling below the knee, where the patellar tendon attaches to the tibial tuberosity. This condition often arises during periods of rapid growth when the bones, muscles, and tendons are developing. Adolescents may experience discomfort during physical activities or when kneeling, climbing stairs, or standing up after sitting for a while. The condition is often self-limiting, meaning that it typically resolves on its own as the adolescent matures and the growth plates close.

In contrast, while patellar tendinitis does involve knee pain, it primarily affects the knee area itself rather than below it, and is often related to overuse injuries in sports. An Achilles tendon rupture occurs at the back of the ankle and involves a different mechanism of injury altogether. The term "Cruel injury" is not a recognized medical condition related to knee or leg pain in adolescents and does not pertain to the symptoms described in the question.