Benign cortical defect: site for an avulsion fracture.

A benign cortical defect in a bone may present itself as a weak site for muscle attachment resulting in an avulsion injury. Such a benign cortical defect may be mistaken for a malignant tumor when the avulsion injury excites irregular, laminated periosteal reaction. We report three patients in whom avulsion fractures occurred at the site of pre-existing benign cortical defects in the distal femur.