Fig. 8
From: Stress fracture of the pelvis and lower limbs including atypical femoral fractures—a review
An elderly female with sudden spontaneous onset of pain. Initial radiographs (shown AP view, a) do not show a focal anomaly. MRI 1 month later performed for persistent pain shows extensive bone marrow oedema-like change in the medial femoral condyle with a subchondral sclerotic area consistent with an insufficiency fracture (b, c; PD-FS; see arrows). The features are those of spontaneous osteonecrosis of the knee, SONK. Note the degeneration/tear of the medial meniscus, a common association of SONK. Radiographic follow-up 1 month after the MRI shows partial cortical collapse of the medial femoral condyle (d, see arrows)