Spontaneous osteonecrosis of the knee

Spontaneous osteonecrosis of the knee presents with acute onset of severe, pain in elderly patients, usually female and usually without a history of trauma. Originally described as idiopathic osteonecrosis, the exact etiology is still debated. Evidence suggests that an acute fracture occurs as a result of chronic stress or minor trauma to a weakened subchondral bone plate. The imaging characteristics on MR reflect the age of the lesion and the symptoms. More appropriate terminology may be "subchondral insufficiency fracture of the knee" or "focal subchondral osteonecrosis". (c) 2008 Elsevier Ireland Ltd. All rights reserved.