IMAGING OF AVASCULAR NECROSIS OF BONE

The etiology of avascular necrosis (AVN) is multifactorial. Independen t of its etiology and localization it shows typical pathologies and ra diological images. In the early stages localized subchondral edema is characteristic. In 50 % of all cases accompanying joint effusion may b e found. Due to necrosis of the cells of bone marrow and bone fibrovas cular, reactions with hyperemia can be delineated. These reactions all ow us to visualize necrosis indirectly. The best imaging methods are M RI and, to a lesser extent, bone scintigraphy. In later stages calcifi cation as well as new bone formation and microfractures are typically demonstrated and visualized best with plain X-rays and CT. Why reparat ions in many cases, particularly in the hip, are incomplete and may st op in any stage is unknown. Over years clinically complete silent AVNs are not an uncommon finding. Prognosis depends on the localization an d size of the AVN. The number of repair mechanisms is best outlined wi th contrast-enhanced MRI and return of fatty marrow.