= AVULSIVE CORTICAL IRREGULARITY = PERIOSTEAL / SUBPERIOSTEAL DESMOID = SUBPERIOSTEAL / CORTICAL ABRASION = SUBPERIOSTEAL CORTICAL DEFECT

= rare fibrous lesion of the periosteum

Peak age: 14–16 (range, 3–17) years; M÷F = 3÷1

Histo: shallow defect filled with proliferating fibroblasts, multiple small fragments of resorbing bone (microavulsions) at tendinous insertions

• no localizing signs / symptoms

Location: posteromedial aspect of medial femoral epicondyle along medial ridge of linea aspera at attachment of adductor magnus aponeurosis; ⅓ bilateral

• area of cortical thickening
• 1–2 cm irregular, shallow, concave saucerlike crater with sharp margin
• lamellated periosteal reaction
• localized cortical hyperostosis proximally (healing phase)
• May be confused with a malignant tumor (eg, osteosarcoma) / osteomyelitis!