Avascular necrosis is a devastating disease that can lead to joint arthrosis for a variety of reasons. Avascular necrosis of the knee joint, which is the most common joint after the hip joint, can be examined in 3 categories: spontaneous osteonecrosis of the knee (SONK), secondary osteonecrosis and post-arthroscopy. Regardless of the categories of osteonecrosis, the treatment of this disease is aimed at stopping further progression or delaying the onset of endstage arthritis of the knee. However, when significant joint surface collapse occurs or there is a sign of degenerative arthritis, joint arthroplasty is the most appropriate treatment option. Currently, non-operative treatment options include observation, nonsteroidal anti-inflammatory drugs (NSAIDs), weightless mobilization, and analgesia as needed. Operative interventions include joint-sparing surgery, unilateral knee arthroplasty (UKA) or total knee arthroplasty (THA), depending on the extent and type of the disease. Generally, when only the underlying subchondral bone is affected, joint preserving procedures, namely arthroscopy, core decompression, osteochondral autograft and bone grafting, are tried in some lesions before and after collapse. Conversely, once severe subchondral collapse has occurred, procedures attempting to save the joint are rarely successful and joint arthroplasty is required to relieve pain.