In this condition there is cessation of the blood supply to one of the condyles of the knee. It leads to secondary osteo-arthritis.

1.It can occur without any primary cause (Idiopathic) 2.Alcohol abuse can lead to development of avascular necrosis 3.Consumption of steroids is another causative factor.

 Sudden onset of pain in the knee joint without any injury.  The pain progresses in nature and intensity.  There may be an effusion.  Movement may be preserved in early stages  There may not be much crepitus.

In the earliest stage radiological signs may not be visible. An MRI scan done in a patient who may be a high risk candidate for this condition may show alteration of signal intensity. In later stages the classic crescent sign of subchondral collapse occurs. There are surprisingly few changes on arthroscopy over the affected condyle.

Symptomatic measures like RICE. When pain is unrelieved then arthroscopy and drilling may bring in neovascularity and pain relief. In advanced stages a unicondylar knee replacement may be advised by the orthopaedician.