Spontaneous osteonecrosis of the knee (SONK) - tibial
Marked knee pain. No history of major traumatic incident.
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Medial tibial condyle subchondral low signal fracture line is seen with surrounding bone marrow edema.
Posterior horn of medial meniscus intrameniscal transverse intermediate to high signal on T1/PD is seen reaching both articular surfaces with blunting of its apex.
Degenerative joint disease.
Patchy areas of intermediate signal on all sequences is noted in femoral, and to less extent the tibial, shafts.
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.