Osteoblastoma is a locally aggressive, osteogenic primary bone tumor primarily affecting the axial skeleton that is known to produce a local inflammatory response surrounding the tumor. This effect, known as the flare phenomenon, has been described primarily for its implications on imaging and diagnosis of osteoblastoma. The main aim of this report is to present an unusual case of osteoblastoma of the posterior ilium associated with unilateral sacroiliac joint ankylosis and chronic right-sided s...