What’s the difference between a bone infarct and avascular necrosis (AVN)?

So, what’s the difference between a bone infarct and avascular necrosis (AVN)? They’re both ischemic processes that end up in osteonecrosis, which obviously means irreversible death of the bone. However, in radiology we use the term bone infarct or medullary infarct when “bone death” occurs in the diaphysis, metaphysis and parts of the non-articulating epiphysis. Avascular necrosis refers to “bone death” within the epiphysis that extends into the subchondral bone. Both can be symptomatic and extremely painful. But, why the difference in terminology? Because AVN has the risk of progressing into articular collapse - converting an osseous problem into an osteoarticular problem, which is usually harder to treat. Bone infarcts can grow in certain conditions of repetitive ischemia and can eventually progress to AVN. Osteonecrosis of the bone has many causes including trauma, certain medications, sickle cell disease among many others. In radiographs, serpiginous lines of sclerosis within the medullary cavity are diagnostic.