[Non-traumatic osteonecrosis of the patella, a rare cause of knee pain].

Non-traumatic osteonecrosis of the patella is a rare cause of knee pain that must be present in the diagnostic discussion of disability of the knee with subacute character. The author describes a case in which the characteristic images had an important role in defining the etiology of disabling knee pain, developing pathophysiological hypotheses that may have contributed to the clinical presentation, including situations of overuse of the joint.