Classic history and presentation: Patients classically present with localized pain that starts as a mild, intermittent, dull ache that persists and gradually increases in intensity. Pain typically becomes increasingly more severe at night and is relieved with NSAIDs.
The order of frequency of affected sites is the appendicular skeleton (lower extremities such as the femur and tibia are more commonly affected than upper extremities), spine, feet (predilection for the talar neck), and hands (predilection for phalanges).
Prevalence: Five percent of all bone tumors and 11% of benign bone tumors (third most common benign bone tumor); one study calculated the incidence of 0.063 / 1 000 000 per year.
Age: 5-40 years. Most patients are younger than age 20.
Sex / gender: Males are more commonly affected (ranges from a 2:1 to 3:1 male-to-female ratio).
Risk factors: Alterations involving chromosome 22q (contains genes involved in cellular proliferation).
Pathophysiology: The exact pathogenesis is unknown. This lesion is considered a neoplasm derived from osteoblasts with 3 concentric layers:
- The central osteoid-rich nidus with dilated vessels and woven bone that may appear calcified.
- A fibrovascular rim that may appear lytic due to resorption by osteoclasts.
- A sclerotic border from new bone formation.
Grade / classification system: OO is considered a stage-2 ("active") lesion according to the Musculoskeletal Tumor Society's (MSTS) staging system for benign tumors.
The lesions are further classified by location as cortical, cancellous, or subperiosteal, with cortical being the most common.
Related topic: osteoma
