Spontaneous osteonecrosis of the knee (SONK)

An 80-year-old woman presented at the emergency department with a sudden non-traumatic pain of the left knee. Supine decubitus plain radiographs of the left knee (Fig. A) reported no evidence of acute traumatic lesion, osteoarthritis bone remodeling, chondrocalcinosis nor mild joint effusion. Chondrocalcinosis crisis was subsequently considered as the final diagnosis and the patient received symptomatic treatment