May Be Caused by

 Common

Chondroblastoma

Chondromalacia

Dorsal defect of patella

Giant cell tumor

Osteochondritis dissecans

Subchondral cyst

 Uncommon

Aneurysmal bone cyst

Bone cyst

Brown tumor of hyperparathyroidism

Enchondroma

Eosinophilic granuloma

Gout

Hemangioma

Intraosseous ganglion

Langerhans cell histiocytosis

Metastasis

Multiple myeloma

Osteoblastoma

Osteomyelitis

Plasmacytoma

Tuberculosis