Chondroblastoma is a rare chondroid tumor, accounting for 1-2% of all primary bone tumors(1,2). It primarily affects adolescents and the young population, between 10-25 years of age with the male-to-female predominance of 2:1(2,5,7). It involves the epiphysis or epiphysis equivalent (apophysis) of bones, most commonly femur, tibia, and humerus (1,3). Other rare sites of occurrence are ilium, acetabulum, patella, small bones of hand and foot, most commonly talus and calcaneum, and temporal bone(1). Rarely, it has been reported in metaphysis and diaphysis of long bones (1,3). It is associated with marked inflammatory reaction in the form of thick periosteal reaction, marrow edema, erosion of cartilage, and joint effusion which are better seen on MR imaging, mimicking the imaging findings of other benign bony entities like osteoid osteoma and eosinophilic granuloma in children and stress fracture in adults and infection in both(3,4,6,9,14). We hereby present a case of chondroblastoma of the distal femur presenting with synovitis of the knee joint.
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