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.