A 15-year-old basketball player presents with painful lumps on his knees. What condition is best described?

The condition described in the scenario is best identified as Osgood-Schlatter disease. This condition is commonly seen in adolescents who are involved in sports activities, particularly those that involve running and jumping, such as basketball. Osgood-Schlatter disease is characterized by painful lumps that develop at the tibial tuberosity, which is where the patellar tendon attaches to the tibia.

The pain typically arises during physical activity and is often aggravated by kneeling, climbing stairs, or running. The condition results from repeated stress and tension on the growth plate (tibial tuberosity) during the period of rapid bone growth, which is common during adolescence.

This aligns with the symptoms presented in the case of a 15-year-old basketball player, making it the most likely diagnosis. On the other hand, osteosarcoma usually presents with persistent pain and swelling that may not be limited to a specific activity or a common age range like Osgood-Schlatter. Juvenile rheumatoid arthritis involves more widespread joint symptoms and often affects multiple joints, not just localized pain at the knee. Paget's disease is typically seen in older adults, characterized by abnormal bone remodeling, thus making it an unlikely diagnosis for a teenager.