Osteoid Osteoma

Osteoid osteoma was first described by Jaffe in 1935 and accounts for 10% of all benign bone tumors.  It is neither locally aggressive nor does it have the potential for malignant transformation.  This bone tumor frequently affects the long bones of the femur and tibia.  This chapter will focus on osteoid osteomas affecting the foot and ankle. The foot is less commonly affected (2-10%) with the talus being most commonly involved.  An osteoid osteoma presents with a nidus of vascular osteoid with surrounding sclerotic bone. Osteoid osteomas do not exceed a diameter of 2 cm and classify into cortical, cancellous, and subperiosteal subtypes. Osteoid osteomas that occur in long bones are predominantly intracortical.  The majority of osteoid osteomas that present in the foot exhibit minimal periosteal reaction and are of the cancellous and subperiosteal subtypes. The size of the nidus is used to differentiate an osteoid osteoma from an osteoblastoma. Osteoblastomas are typically greater than 2 cm.