Osteochondroma: A common benign bone tumor that can grow near the growth plate, causing a bump on the knee. It can cause pain when pressed on and may grow in size over time, especially during childhood and adolescence.

Ganglion Cyst: A lump under the skin that occurs when fluid accumulates in a sac, often near a joint or tendon. It can cause pain when pressed on and may grow in size over time.
Bursitis: Inflammation of a fluid-filled sac (bursa) that cushions joints and reduces friction between bone and soft tissue. It can cause a painful bump on the knee.
Lipoma: A benign tumor composed of fat tissue that can grow under the skin, causing a bump. It can cause pain when pressed on, especially if it is large or located near a nerve.

Osteosarcoma: A rare but aggressive type of bone cancer that can cause a growing bump on the knee. It is essential to rule out this diagnosis, as it requires prompt treatment.
Infection (e.g., abscess or osteomyelitis): A bacterial or fungal infection that can cause a painful bump on the knee. It is crucial to diagnose and treat infections promptly to prevent serious complications.
Neurofibroma: A benign tumor that grows on nerve tissue, which can cause a bump on the knee. While usually not life-threatening, it can be associated with neurofibromatosis type 1, a genetic disorder that requires monitoring.

Synovial Chondromatosis: A rare condition where cartilage grows in the synovial membrane of a joint, causing a bump on the knee.
Hemangioma: A rare benign tumor composed of blood vessels that can grow under the skin, causing a bump on the knee.
Giant Cell Tumor: A rare, usually benign tumor that can grow on the bone, causing a bump on the knee. While often benign, it can be locally aggressive and requires monitoring.