MRI OF AVASCULAR NECROSIS OF BONE

Avascular necrosis (AVN) is characterized by death of both trabecular bone as well as bone marrow elements. Weight-bearing bone becomes mech anically weakened and may eventually collapse, secondarily leading to osteoarthritis and debilitating pain. Early diagnosis and treatment of this entity are crucial because it affects relatively young individua ls, and treatment options for advanced disease are limited. Magnetic r esonance imaging (MRI) has emerged as the modality of choice for the e valuation of avascular necrosis of bone. We will discuss applications of MRI for early diagnosis, for monitoring therapy, and for its potent ial role in assessing individuals al risk of AVN. Although bone scinti graphy using single photon emission computed tomography (CT) may be ne arly as accurate as MRI, MRI offers a more specific diagnosis in the p atient who presents with hip pain of uncertain etiology. In addition, lesion size and location can be more easily assessed on magnetic reson ance images, and this has been shown to relate to prognosis and need f or treatment. We will review the pathophysiologic mechanisms of AVN an d the current use of MRI in the diagnosis of this condition.