Spontaneous osteonecrosis of the knee (SONK) associated with degenerative joint disease and posterior horn of medial meniscus degenerative tear.

The absence of trauma in history is typical for SONK, since the insult is usually repititive microtauma on osteoporotic bone, especially in old females.

The femoral and tibial marrow signal abnormality is mostly yellow to red marrow reconversion.