Osteonecrosis of the femoral head extending into the femoral neck.

Osteonecrosis of the femoral head (ONFH) is an ischemic disorder that can lead to femoral head collapse and secondary osteoarthritis. Although the condition is usually limited to the femoral head, we report a rare case of biopsy-proven ONFH extending into the femoral neck, which required hip replacement surgery. We emphasize the imaging features of this condition and briefly discuss its potential relevance.