Developmental defects of the distal femoral metaphysis.

The posteromedial aspect of the distal end of the femur in the area of insertion of the adductor magnus is the site of occurrence of a developmental defect that may have the roentgenographic characteristics of a malignant bone tumor. As it is asymptomatic, this common defect is almost always an incidental finding, but it has been confused with osteosarcoma. The lesion is thought to be due to trauma or the avulsion of small bits of bone at the site of insertion of the adductor magnus muscle. Histologically the lesion has been mistaken for osteosarcoma because of the immature reactive bone and fibrous tissue presnet. It is usually possible to identify these defects roentgenographically and avoid biopsy.