Metaphyseal fibrous defect (also called nonossifying fibroma or fibrous cortical defect of bone) is the most common benign fibrous bone lesion. It is believed to be due to an ossification defect in the skeletally immature (children and adolescents). It is typically asymptomatic and often detected incidentally on x-ray following trauma, most commonly in the metaphysis of long bones (distal femur, distal tibia, or proximal tibia). A rare occurrence in the mandible has been reported in the literature. Nonossifying fibromas may occur in multiple sites in 40%-50% of cases. Pathologic fracture may be observed at the site of large lesions, but this is uncommon.

As with any fibrous bone lesion, care must be taken to rule out malignancy.

Management of asymptomatic, incidentally discovered metaphyseal fibrous defect generally calls for observation, as lesions tend to resolve as bones reach maturity. Pain or pathologic fracture may call for additional measures, including curettage and bone graft.