Exostosis-like intra-articular periosteal osteoblastoma: a rare case.

Osteoblastoma is a relatively rare benign bone tumor, most often located in the vertebral column or metaphysis of the long bones, particularly the femur and the tibia. Periosteal osteoblastoma is the least common type. Exostosis-like appearance is not common even in periosteal osteoblastoma, a very rare type of this tumor. In addition, an intraarticular location is uncommon for osteoblastomas. Here we report the case of a 25-year-old man with intra-articular exostosis-like periosteal osteoblastoma of the hip that resulted in impingement and osteoarthritis.