This young adult was being treated for a leukaemia with high dose steroids, with bilateral knee pain.
Avascular necrosis (or more correctly osteonecrosis) is a generic term referring to ischaemic death of the constituents of bone. Ischaemic necrosis is reserved for subchondral osteonecrosis (click image, white arrows) whereas bone infarct refers to medullary osteonecrosis (black arrow).
There are many causes of osteonecrosis: steroids, alcohol and sickle cell disease are some of the more common ones (depending on population demographics). A longer list can be recalled with the mnemonic PLASTIC RAGS
For more about osteonecrosis, please visit Radiopaedia.org here.
Reference: Bone and Joint imaging - Resnick
Credit: Dr Frank Gaillard