Osteochondritis dissecans of the knee: Imaging, instability concept, and criteria.

Osteochondritis dissecans of the knee is an idiopathic, focal, subchondral-bone abnormality that can cause instability or detachment of a bone fragment and overlying articular cartilage, with subsequent progression to osteoarthritis. The degree of lesion instability is best assessed by magnetic resonance imaging. Unstable lesions require operative management with fragment fixation. Level of evidence : V.