What is Avascular Necrosis?

generally associated with hip bone.in this head of Femur does not get enough blood supply and gets destroyed. causing loss of the hip joint function

Avascular means no blood supply, whereas necrosis means death of a tissue (in this case it's bone)....
so....
Avascular necrosis is a disease resulting from the temporary or permanent loss of the blood supply to the bones. Without blood, the bone tissue dies and causes the bone to collapse. If the process involves the bones near a joint, it often leads to collapse of the joint surface. This disease also is known as osteonecrosis, aseptic necrosis, and ischemic bone necrosis.
It most commonly affects the epiphysis of long bones (ie: femur...as the last answer says) but can affect other bones in the body.
Causes range from injury, drug use (steroids & alcohol), pancreatitis, radiation therapy, etc.
Symptoms include: gradual pain, all the way up to loss of joint function. Early stage...some people don't have symptoms.
Dx (diagnosis): X-ray, biopsy, bone scan, CT scan, functional evaluation of the bone.
Tx: (treatment):
depends on the following:
The age of the patient
The stage of the disease - early or late
The location and amount of bone affected - a small or large area
The underlying cause of avascular necrosis - with an ongoing cause such as corticosteroid or alcohol use, treatment may not work unless use of the substance is stopped.

treatments used include medication & surgery

Hope that helps :)
merlin the cat