A 15-year-old male presents with knee pain and a painful lump below the knee. What is the most likely diagnosis?

Osgood-Schlatter disease is the most likely diagnosis for this 15-year-old male presenting with knee pain and a painful lump below the knee. This condition is characterized by inflammation of the patellar tendon at its insertion point on the tibial tuberosity. It is particularly common in adolescents during periods of rapid growth, and it often presents with localized pain and swelling in the area where the tendon attaches to the bone.

The presence of a painful lump below the knee is a classic sign of Osgood-Schlatter disease, which can become prominent due to repeated stress and activity, especially in young athletes involved in sports that require running, jumping, or squatting. This condition typically resolves with conservative management, including rest, ice, and limiting activities that aggravate the symptoms.

Understanding the broader context of the knee in adolescent patients can help differentiate it from other potential conditions, such as patellar tendonitis, which usually presents with pain more centered around the patellar region, a meniscus tear characterized by joint locking or swelling rather than a distinct lump, and a fractured patella that presents with severe pain and possibly an inability to move the knee. Recognizing the specific clinical features and typical age of onset is key in arriving at the