Avascular necrosis cannot spread from one body part to the other.  However, there are certain conditions, which cause avascular necrosis in numerous joints of the body.  Avascular necrosis may affect numerous bones in certain disorders.
However, if a patient has avascular necrosis in a certain bone or a certain joint, the avascular necrosis by itself does not spread to other parts.  There are certain conditions, which are certainly localized, as an example; trauma to the hip, which causes avascular necrosis of the hip and the patients should expect that in such a scenario, in the absence of other conditions the avascular necrosis is going to stay in the same body part.