Intraarticular epiphyseal osteoid osteoma of the distal femur.

A 9-year-old boy had pain in the medial side of the right knee with limited range of motion and limping. Roentgenography showed a small sclerotic shadow (8 X 8 mm2) in the medial femoral condyle, where bone scintigraphy revealed a high uptake area and angiography showed a nidus. Five months after initial presentation, en bloc excision was done through the posteromedial approach. Histological examination showed a network of osteoid trabeculae, differentiated osteoblasts, and multinucleated giant cells in this nidus, which were compatible with those of osteoid osteoma. Complete relief of pain was obtained at follow-up 1 year after the operation.