Imaging of avascular necrosis of bone.

The etiology of avascular necrosis (AVN) is multifactorial. Independent of its etiology and localization it shows typical pathologies and radiological images. In the early stages localized subchondral edema is characteristic. In 50 % of all cases accompanying joint effusion may be found. Due to necrosis of the cells of bone marrow and bone fibrovascular, reactions with hyperemia can be delineated. These reactions allow us to visualize necrosis indirectly. The best imaging methods are MRI and, to a lesser extent, bone scintigraphy. In later stages calcification as well as new bone formation and microfractures are typically demonstrated and visualized best with plain X-rays and CT. Why reparations in many cases, particularly in the hip, are incomplete and may stop in any stage is unknown. Over years clinically complete silent AVNs are not an uncommon finding. Prognosis depends on the localization and size of the AVN. The number of repair mechanisms is best outlined with contrast-enhanced MRI and return of fatty marrow.